Update: Washington State pertussis epidemic

Andrew received his first dose of hepatitis B vaccine minutes after he was born. My intention had been to write an entry on hepatitis B but, as you can see, I've had my hands full.

In April of this year, Washington State Health Secretary Mary Selecky declared that pertussis (whooping cough) had reached epidemic level in the state. At that time, 640 cases had been reported to the state Department of Health since the beginning of the year.

Last Friday (July 20, 2012), the Centers for Disease Control and Prevention (CDC) published a summary of the current pertussis epidemic in Washington State in the Morbidity and Mortality Weekly Report (MMWR). Between January 1^st and June 16^th, 2,520 cases had been reported – 13 times the number reported during the same time last year. Illinois, New York and Wisconsin have also had dramatic increases in the numbers of pertussis cases compared to last year. In fact, nearly half of all the states have reported more than double the numbers of cases in the first six months of 2012 than their total numbers of cases in 2011 (CDC, 2012a).

Overall, the national incidence of pertussis is increasing. In 2011, a total of 8,284 cases of pertussis were reported in the U.S. So far this year, 17,920 cases have been reported. One notable exception is California. A total of 7,195 cases of pertussis were reported during the 2010 epidemic in California. Last year 1,709 cases were reported in California and, so far this year, 275 cases have been reported.

I included this graph in my previous post on pertussis vaccines:

CDC, 2002

What we see is a sharp decrease in the incidence of pertussis after the introduction of whole-cell pertussis vaccine in the mid-1940's to the lowest point in 1976. Since then, there has been a gradual increase in pertussis incidence.

There are a number of factors that could be contributing to the increase in the number of pertussis cases. One is simply that pertussis is being recognized and diagnosed more frequently. Pertussis used to be thought of as a childhood disease and immunity to pertussis was believed to be life-long. We now know that immunity to pertussis wanes and that adults usually don’t have the severe symptoms that are seen in children.

The epidemiological data from the current pertussis epidemic in Washington State and the 2010 California epidemic suggests that immunity to pertussis from acellular pertussis vaccines wanes more quickly than immunity from whole-cell pertussis vaccines, which are no longer used in the U.S.

Whereas acellular pertussis vaccines contain up to 5 antigens, whole-cell pertussis vaccines contained around 3,000 antigens. Whole-cell vaccines are highly effective; unfortunately, they also have a high occurrence of adverse events ("side effects"). Acellular vaccines have fewer side effects and appear to be highly effective for the first two years after immunization, but immunity seems to wane more quickly than after immunization with a whole-cell pertussis vaccine.

So, why should my child or I receive a pertussis vaccine if I can still get pertussis anyway? There are several reasons. Even though most of the cases of pertussis are in vaccinated people, the attack ratio is much higher in unvaccinated people. Unvaccinated children are eight times more likely to get pertussis than children who have received all of the recommended doses of DTaP (CDC, 2012b). Unvaccinated children with pertussis are more likely to have severe disease, cough longer, and infect other people than vaccinated children (Baptista et al, 2006; Préziosi & Halloran, 2003; Tozzi et al., 2003).

No vaccine is 100% effective. We have known that immunity to pertussis wanes, but it now appears that immunity from acellular vaccines wanes more quickly than we thought. Nevertheless, acellular pertussis vaccines remain our best defense against pertussis.

On a personal note, one of my duties as a nurse epidemiologist in a county health department is to investigate cases of notifiable diseases. State law requires health care providers to report notifiable diseases to their local health jurisdiction (LHJ). Pertussis is one of those diseases. When the health department receives notification of a case of pertussis, one of my colleagues or I contact the parent of the child or the person with pertussis and complete a case report form. We then submit the data that we collect to the Washington State Department of Health and from there it is sent to the CDC. In this case, the CDC published their analysis of Washington State pertussis data in the MMWR cited above. In other words, the CDC report includes data that I collected.

References:

Águas, R., Gonçalves, G., & Gomes, G. M. G. (2006). Pertussis: increasing disease as a consequence of reducing transmission. Lancet Infectious Diseases, 6(2), 112-117. doi.org/10.1016/S1473-3099(06)70384-X.

Baptista, P. N., Magalhães, V., Rodrigues, L. C., Rocha, M. A. W., & Pimentel, A. M. (2006). Pertussis vaccine effectiveness in reducing clinical disease, transmissibility, and proportion of case with positive culture after household exposure in Brazil. Pediatric Infectious Disease Journal, 25(9), 844-846.

Centers for Disease Control and Prevention. (2002). Pertussis – United States, 1997-2000. Morbidity and Mortality Weekly Report, 51(4), 73-76. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5104a1.htm.

Centers for Disease Control and Prevention. (2012). Notifiable diseases and mortality table. Morbidity and Mortality Weekly Report, 61(28), ND-382-ND-395. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6128md.htm.

Center for Disease Control and Prevention. (2012). Pertussis epidemic – Washington, 2012. Morbidity and Mortality Weekly Report, 61(28), 517-522. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6128a1.htm.

Offit, P. A., Quarles, J., Gerber, M. A., Hackett, C. J., Marcuse, E. K., Kollman, T. R. et al. (2002). Addressing parents’ concerns: do multiple vaccines overwhelm or weaken the infants immune system? Pediatrics, 109(1), 124-129. http://pediatrics.aappublications.org/content/109/1/124.full.

Préziosi, M-P. & Halloran, E. (2003). Effects of pertussis vaccination on disease: vaccine efficacy in reducing clinical severity. Clinical Infectious Diseases, 37(6), 772-779. http://cid.oxfordjournals.org/content/37/6/772.long.

Rohani, P. & Drake, J. M. (2011). The decline and resurgence of pertussis in the US. Epidemics, 3(3-4), 183-188. doi: 10.1016/j.epidem.2011.10.001.

Tozzi, A. E., Ravá, L., Ciofi degli Atti, M. L., Salmaso, S., Progetto Pertosse Working Group. (2003). Clinical presentation of pertussis in unvaccinated and vaccinated children in the first six years of life. Pediatrics, 112(5), 1069-1075. http://pediatrics.aappublications.org/content/112/5/1069.full

Witt, M. A., Katz, P. H., & Witt, D. J. (2012). Unexpectedly limited durability of immunity following acellular pertussis vaccination in preadolescents in a North American outbreak. Clinical Infectious Diseases, 54(12), 1730-1735. doi: 10.1093/cid/cis287.

Ladies and gentlemen,

please allow me to introduce Andrew Craig Rollosson.

As he was walking by the Sea of Galilee, he saw two brothers, Simon who is called Peter, and his brother Andrew, casting a net into the sea; they were fishermen. He said to them, “Come after me, and I will make you fishers of men.” At once they left their nets and followed him.
- Matthew 4:18-20

The next day John was there again with two of his disciples, and as he watched Jesus walk by, he said, “Behold, the Lamb of God.” The two disciples heard what he said and followed Jesus. Jesus turned and saw them following him and said to them, “What are you looking for?” They said to him, “Rabbi” (which translated means Teacher), “where are you staying?” He said to them, “Come, and you will see.” So they went and saw where he was staying, and they stayed with him that day. It was about four in the afternoon. Andrew, the brother of Simon Peter, was one of the two who heard John and followed Jesus. He first found his own brother Simon and told him, “We have found the Messiah”
- John 1:35-41

Immunization laws

Our son - nose, lips, chin, and cheek.

I started this blog to discuss childhood immunizations but I've spent the last six months discussing vaccines and pregnancy, adult vaccines, and some immunization principles. Our son will born soon - very soon - so it's time for me to shift gears.

A number of surveys of adults have found that the majority of parents vaccinate their children according to the recommended immunization schedule and consider their health care providers to be reliable sources of immunization information (Gust et al., 2008; Kennedy et al., 2011). Although most parents of young children in the U.S. do not remember epidemics of vaccine-preventable diseases, most parents recognize that vaccines are an important way to prevent diseases (Freed et al., 2010; Gust et al., 2005). I suspect that, other than when they register their children for school and must present their children's immunization records, most parents don't give much thought to school immunization laws. Nevertheless, given some of the comments I hear from parents as well as news stories about mandated vaccines, I think there is some confusion about vaccine laws in the U.S.

First, school immunization laws are state laws. There are no federal immunization laws.

There are two operating divisions of the U.S. Department of Health and Human Services that are involved with regulating and recommending vaccines. The Food andDrug Administration (FDA) approves and licenses vaccines marketed in the U.S. The Center for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) publishes immunization recommendations. Occasionally, there are some differences between what the FDA approves and what the ACIP recommends. For example, the FDA approved herpes zoster (shingles) vaccine for persons 50 years of age and older while the ACIP recommends shingles vaccines for persons 60 years of age and older.

Neither the FDA nor the CDC mandate vaccines. In fact, the CDC is not a regulatory agency.

In Jacobson v. Massachusetts (1905), the U.S. Supreme Court affirmed states' authority to mandate vaccines. The court recognized the duty of the state to preserve the safety of the general public. Each state has its own school immunization laws and the requirements for school entry differ from state to state. In general, the states follow the ACIP recommendations; however, some vaccines recommended by the ACIP are not required by every state. One example is human papillomavirus (HPV) vaccine. The ACIP recommends HPV vaccine for males and females ages 9 through 26 years. Currently, the only state to require HPV vaccination for school entry is Virginia (6^th grade, girls only).

All states require DTaP/Tdap, MMR, polio, and varicella (chickenpox; documentation of immunity from natural infection may be acceptable) immunizations for school entry. The number of doses required varies between states as do the requirements for other vaccines such as hepatitis B, hepatitis A, meningococcal, and pneumococcal vaccines.

Just as the school immunization laws vary between states, immunization exemption laws also vary between states. There are three types of immunization exemptions: medical, religious, and personal/philosophical. Children for whom an immunization is contraindicated may obtain a medical exemption, which usually requires documentation of the reason for the exemption from a medical provider. All 50 states allow medical exemptions. Forty-eight states allow religious exemptions and 20 states allow personal/philosophical exemptions.

The requirements for obtaining an exemption vary between states. Some states require only a parent's signature on an exemption forum to obtain either a religious and/or personal/philosophical exemption. Other states have additional requirements. Last year, the Washington State legislature changed the requirement for obtaining a person/philosophical requirement. Prior to 2011, a parent or guardian could simply sign an exemption form. ESB 5005 requires the signature of a licensed health care professional who has counseled the parent on the benefits of vaccinating and the risks of not vaccinating.

Not surprisingly, states in which exemptions are easily obtained tend to have higher exemption rates (Rota et al., 2001). Several studies have concluded that nonmedical exemptions increase the incidence of vaccine-preventable diseases and increase the risk of those diseases in babies too young to have been immunized, people with medical contraindications to vaccines, and those who received the vaccine but did not develop adequate immunity (primary vaccine failure) or lost their immunity (secondary vaccine failure) (Feikin et al., 2000; Glanz et al., 2009; May & Silverman, 2003; Omer, Engler, et al., 2008; Omer, Pan, et al., 2006; Omer, Salmon, et al., 2009).

Students with immunization exemptions may be excluded from school during an outbreak of a vaccine-preventable disease (NNII, 2011). In Washington State, a local (county) health officer may require non-immunized students to be excluded from school during an outbreak (WAC 246-110-020).

Parents of infants and school-age children should review the immunization requirements for the state in which you live. See additional information below.

The ACIP recommends a dose of hepatitis B vaccine at birth, so that will be the topic of my next post.

Additional information:

Immunization Action Coalition:

• Links to stateimmunization websites

CDC:

• Requirements & Laws

National Network for Immunization Information:

• Indications, Recommendations and Immunization Mandates
 
• Exemptions from Immunization Laws

References:

Feikin, D. R., Lezotte, D. C., Hamman, R. F., Salmon, D. A., Chen, R. T., Hoffman, R. E. (2000). Individual and community risks of measles and pertussis associated with personal exemptions to immunizations. JAMA, 284(24), 3145-3150. http://jama.jamanetwork.com/article.aspx?articleid=193407.

Glanz, J. M., McClure, D. L., Magid, D. J., Daley, M. F., France, E. K., Salmon, D. A. et al. (2009). Parental refusal of pertussis vaccination is associated with an increased risk of pertussis infections in children. Pediatrics, 123(6), 1446-1451. http://pediatrics.aappublications.org/content/123/6/1446.long.

Freed, G. L., Clark, S. J., Butchart, A. T., Singer, D. C., & Davis, M. M. (2010). Parental vaccine safety concerns in 2009. Pediatrics, 125(4), 654-659. http://pediatrics.aappublications.org/content/125/4/654.full.

Gust, D., Brown, C., Sheedy, K., Hibbs, B., Weaver, D., & Nowak, G. (2005). Immunization attitudes and beliefs among parents: beyond a dichotomous perspective. American Journal of Health Behavior, 29(1), 81-92. http://www.ncbi.nlm.nih.gov/pubmed/15604052.

Gust, D. A., Darling, N., Kennedy, A., & Schwartz, B. (2008). Parents with doubts about vaccines: which vaccines and reasons why. Pediatrics, 122(4), 718-725. http://pediatrics.aappublications.org/content/122/4/718.full.

Kennedy, A., Basket, M., & Sheedy, K. (2011). Vaccine attitudes, concerns, and information sources reported by parents of young children: results from the 2009 HealthStyles survey. Pediatrics, 127(Supple. 1). S92-S99. Retrieved June 10, 2011 from http://pediatrics.aappublications.org/content/127/Supplement_1/S92.full.html.

May, T. & Silverman, R. D. (2003). ‘Clustering of exemptions’ as a collective action threat to herd immunity. Vaccine, 21, 1048-1051. http://www.sciencedirect.com/science/article/pii/S0264410X02006278.

National Network for Immunization Information. (2011). Exemptions from immunization laws. Retrieved July 7, 2012 from http://www.immunizationinfo.org/issues/immunization-policy/exemptions-immunization-laws.

Omer, S. B., Enger, K. S., Moulton, L. H., Halsey, N. A., Stokley, S., & Salmon, D. A. (2008). Geographic clustering of nonmedical exemptions to school immunization requirements and associations with geographic clustering of pertussis. American Journal of Epidemiology, 168(12), 1389-1396. http://aje.oxfordjournals.org/content/168/12/1389.long.

Omer, S. B., Pan, W. K. Y., Halsey, N. A., Stokley, S., Moulton, L. H., Navar, A. M. et al. (2006). Nonmedical exemptions to school immunization requirements: secular trends and association of state policies with pertussis incidence. JAMA, 296(14), 1757-1763. http://jama.jamanetwork.com/article.aspx?articleid=203593.

Omer, S. B., Salmon, D. A., Orenstein, W. A., deHart, P., Halsey, N. (2009). Vaccine refusal, mandatory immunization, and the risk of vaccine-preventable diseases. New England Journal of Medicine, 360(19), 1981-1988. http://www.nejm.org/doi/full/10.1056/NEJMsa0806477.

Rota, J. S., Salmon, D. A., Rodewald, L. E., Chen, R. T., Hibbs, B. F. et al. (2001). Process for obtaining nonmedical exemptions to state immunization laws. American Journal of Public Health, 91(4), 645-648. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1446650.

Disease eradication

First, Holly had another ultrasound on last week – it's a boy! (but I'm not going to show you that picture).

Next, Mary had surgery three weeks ago. The neurosurgeon removed about 90 to 95 percent of the tumor. Mary transferred out of the hospital into a skilled nursing facility yesterday. She is enthusiastically participating in her therapies and has regained some strength in her left side. Thanks for your prayers.

I forgot to mention that I became a published author May 1^st: Improving Immunization Coverage in a Rural School District in Pierce County, Washington. I wrote the article but, since I wasn't directly involved in the study, I'm the last author listed. Now I need to get my cerebral malaria paper published!

Disease eradication

As I discussed in my post on diseases that have been eliminated from the U.S. by vaccines, the difference between disease elimination and eradication is that elimination is the reduction of the incidence of a disease to zero within a geographic region and elimination is the global incidence of a disease to zero. Another important distinction is that once a disease has been eradicated, further efforts to control that disease are no longer necessary.

So far, smallpox is the only disease that has been eradicated, so smallpox vaccination is no longer recommended for the general population. I'm a baby boomer with a smallpox vaccination scar. Holly is Generation X and does not have a smallpox vaccination scar.

There are currently two ongoing disease eradication initiatives: poliomyelitis ("polio") and dracunculiasis (Guinea worm disease).

For a disease to be considered eradicable it must meet a number of biological, economic, political, and societal criteria. Walter Dowdle outlined three primary indicators:

• There must be an effective intervention to interrupt transmission
• There must be a diagnostic tool that is sensitive and specific enough to detect the infection
• Humans must be essential to the lifecycle of the infecting agent

For most eradicable diseases, a vaccine is the intervention used to interrupt transmission, but that's not the case for dracunculiasis.

For smallpox, the diagnostic tool used to detect infection was clinical presentation: a person infected with the variola (smallpox) virus had the characteristic lesions of that disease. Unlike some other infections, there was no asymptomatic carriage of variola virus. People who were infected got the disease. For polio, the diagnostic tool is clinical presentation and detection of poliovirus in stool.

In general, for humans to be essential to the lifecycle of the infecting agent means that there can be no non-human reservoirs. Two examples of diseases for which there are non-human reservoirs that come to mind are yellow fever, which infects humans and monkeys, and influenza, which infects other mammals and birds.

I won't go into the details of the economic/political/societal requirements for disease eradication. The short version is that there must be sustained political will to eradicate a disease. Since disease eradication is a global effort, you can imagine the complexities of arriving at an agreement that eradication of a disease is a worthwhile goal.

Removing a Guinea worm
CDC/ The Carter Center

The strategies used to eradicate a disease will vary with the disease and its mode of transmission. There is no vaccine for Guinea worm disease, which is transmitted through water. Instead, filtering or boiling drinking water are two of the techniques used to prevent transmission.

Polio eradication relies on three vaccination strategies:

• High routine coverage with oral polio vaccine
• National Immunization Days
• Supplemental "mop-up" campaigns

As the immunization outreach coordinator at the Chiri Health Center in Ethiopia, I was involved with achieving and maintaining high routine immunization coverage in the neighboring villages. During National Immunization Days, our clinic staff would be recruited to go door-to-door to administer oral polio vaccine to all of the infants and young children within those households. I recall spending part of a day walking around Addis Ababa looking for chalk for the vaccinators to mark the doors of houses they had visited. Fortunately, there were no outbreaks of polio in our area that required mop-up immunization.

In addition to immunization, the clinic staff were responsible to report any new cases of acute flaccid paralysis (AFP) that might have been paralytic polio. Surveillance is an integral part of an eradication program. Had we seen a case of AFP in the clinic, we would have been required to send a stool specimen from the child to Addis Ababa to test for the presence of poliovirus.

Transmission of one of the three wild poliovirus types has not been detected anywhere in the world since 1999. Wild poliovirus transmission has been interrupted in all but four countries: Afghanistan, India, Nigeria, and Pakistan. Poliovirus transmission had ceased, but has been reestablished in Angola, Chad, and the Democratic Republic of the Congo. Outbreaks of polio occur in countries where poliovirus has been reimported.

Until polio has been eradicated, there is a continuing threat of importation from countries where poliovirus continues to be transmitted.

I'll spend more time talking about polio and polio vaccines in a few months when our baby is due for his first dose of polio vaccine.

More information:

• Global Polio Eradication Initiative
• The Carter Center: Guinea Worm Disease Eradication

References:

Dowdle, W. A. (1998). The principles of disease elimination and eradication. Morbidity and Mortality Weekly Report, 48(Supple. 1), 23-27. http://www.cdc.gov/mmwr/preview/mmwrhtml/su48a7.htm.

Fine, P. E. M. & Mulholland, K. (2008). Community immunity. In S. A. Plotkin, W. A. Orenstein, & P. A. Offit (Eds.) Vaccines (5th Ed.) [Electronic version].

Hadler, S. C., Dietz, V., Okwo-Bele, J. M., & Cutts, F. T. (2008). Immunization in developing countries. In S. A. Plotkin, W. A. Orenstein, & P. A. Offit (Eds.) Vaccines (5th Ed.) [Electronic version].

Heymann, D. L. (2011). Disease eradication and control. In R. L. Guerrant, Walker, D. H., & Weller, P. F. (Eds.) Tropical infectious diseases, principles, pathogens and practice (3^rd Ed.). [Electronic version].

Olsen, B., Munster, V. J., Wallensten, A., Waldenström, J., Osterhaus, A. D. M. E., Fouchier, R. A. M. (2006). Global patterns of influenza A virus in wild birds. Science, 21(312), 384-388. http://www.sciencemag.org/content/312/5772/384.full.

Community immunity (herd immunity)

Pardon my hiatus. I made a lateral transfer to epidemiology and I'm still getting used to my new work hours.

Craig and Mary, April 23, 2005
Father and mother of the bride



I had planned to post the following thread on Mother's Day. Instead, my father-in-law and I accompanied Mary, my mother-in-law, to an emergency department where she had a head CT and then a brain MRI which disclosed a glioblastoma – the worst type of brain tumor.

Holly and I met in 2003 while I was taking care of Seth, who had sustained a severe traumatic brain injury in a motor vehicle accident. Seth has remains in a minimally conscious state. Despite her rheumatoid arthritis, Mary has cared for Seth at home for nearly seven years. Now, Mary is in the care of some of the same nurses who cared for Seth eight and a half years ago and the best neurosurgeon I have known in my career as a neuro nurse. She will have surgery on Monday.

Mary and Craig welcomed me into their home as their son seven years ago. Mary has been an inspiration to everyone who knows her. Please be in prayer for her.

Community immunity: 

Another study on the incidence of measles was published shortly after my last post: Assessment of the 2010 global measles mortality reduction goal. The investigators found that the number of deaths from measles worldwide has decreased by 74% between 2000 and 2010. Measles outbreaks in Africa and immunization program delays in India prevented the goal of 90% reduction in measles deaths from being achieved. Forty-seven percent of the estimated 139,300 measles deaths in 2010 occurred in India and 36% occurred in Africa.

In previous posts I've talked about some ways that vaccines indirectly protect people other than the recipient. Maternal antibodies are transported across the placenta, protecting newborn babies from neonatal tetanus and may protect babies against pertussis. Cocooning is another strategy to protect babies against pertussis.

Communicable diseases are diseases that are transmitted from one person to another. For a communicable disease to be transmitted, a susceptible person must be exposed to the infecting agent. Most vaccine-preventable diseases are transmitted by contact with someone who is infected with a virus or bacterium (Yellow fever, which is transmitted by mosquitoes, is one exception that comes to mind. Tetanus is a vaccine-preventable disease that is not communicable). The probability that a susceptible person will be exposed to an infected person decreases with the proportion of immune people in a population. Therefore, susceptible individuals are protected by other people's immunity. This is known as "community immunity" or "herd immunity."

Last year there were 222 cases of measles in the U.S. Seventy-two cases were imported from outside of the U.S., and 128 cases were known to be associated with the imported case (CDC, 2012b). The basic reproductive number (R₀, or "R naught") for measles is 14, which means that in a susceptible population, a person with measles will transmit the virus to 14 other people, who will each transmit it to 14 people until there are no longer enough susceptible people in the population to sustain transmission. The size of the measles outbreaks in U.S. last year were limited by the small number of people in the country who are susceptible to measles; that is, most people in the U.S. are immune to measles. The national average for receipt of at least one dose of measles-containing vaccine (MCV) is 90% (CDC, 2012a).

Examples of indirect vaccine protection:

A recent study that demonstrated a protective effect of vaccines on people other than the recipients was the 2010 Hutterite study. During the 2008-2009 influenza season the study investigators randomized 46 Hutterite colonies in western Canada. Children ages 3 to 15 years in 22 of the colonies received seasonal influenza vaccine and children in 24 of the colonies received hepatitis A vaccine as a control (rather than a placebo). During the flu season, the numbers of cases of influenza were counted in all of the participating colonies. At the end of the flu season, the numbers of cases of influenza in the colonies in which children received influenza vaccine and colonies in which children received hepatitis A vaccine were compared. The study investigators found that the seasonal influenza vaccine given to children was 61% effective in preventing flu in colony members who did not receive the vaccine (Loeb et al., 2010).

From 1998 to 2003, 7-valent pneumococcal conjugate vaccine dramatically reduced the incidence of invasive pneumococcal disease (IPD) in children less than 5 years of age who received the vaccine. At the same time, the incidence of IPD also decreased in all age groups, with the largest rate of reduction in people aged 65 years and older. The decrease in incidence was seen only in seven pneumococcal serotypes included in the vaccine, so it is unlikely that the decreased incidence was caused by some other factor. Overall, 69% of the protective effect of pneumococcal vaccine was seen in people who had not received the vaccine (CDC, 2005).

One more example is in the near elimination of deaths due to chickenpox (yes, people die from chickenpox) after the introduction of chickenpox vaccine. The reduction in the number of deaths due to chickenpox was seen in all age groups, not just those who had received the vaccine (Marin, Zhang, & Seward, 2011).

In a previous post, I talked about diseases that have been eliminated from the U.S. by vaccines. Next, I'd like to discuss disease eradication.

More information:

• National Institute of Allergy and Infectious Diseases: Community Immunity ("Herd" Immunity)
• The College of Physicians of Philadelphia: Herd Immunity

References:

Centers for Disease Control and Prevention. (2005). Direct and indirect effects of routine vaccination of children with 7-valent pneumococcal conjugate vaccine on incidence of invasive pneumococcal disease – United States, 1998-2003. Morbidity and Mortality Weekly Report, 54(36), 893-897. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5436a1.htm.

Centers for Disease Control and Prevention. (2012). Epidemiology and prevention of vaccine-preventable diseases (12^th Ed.). http://www.cdc.gov/vaccines/pubs/pinkbook/index.html.

Centers for Disease Control and Prevention. (2012). Measles – United States, 2011. Morbidity and Mortality Weekly Report, 61(15), 253-257. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6115a1.htm.

Fine, P. E. M. & Mulholland, K. (2008). Community immunity. In S. A. Plotkin, W. A. Orenstein, & P. A. Offit (Eds.) Vaccines (5th Ed.) [Electronic version]

Heyman, D. L. (2011). Disease eradication and control. In R. L. Guerrant, D. H. Walker, & P. F. Weller (Eds.). Tropical infectious diseases: principles, pathogens and practice (3^rd Ed.). [Electronic version].

Loeb, M., Russell, M. L., Moss, L., Fonesca, K., Fox, J., Earn, D. J. D. et al. (2010). Effect of influenza vaccination of children on infection rated in Hutterite communities. JAMA, 303(10), 943-950. http://jama.ama-assn.org/content/303/10/943.full.

Marin, M., Zhang, J. X., & Seward, J. F. (2011). Near elimination of varicella deaths in the US after implementation of the vaccination program. Pediatrics, 128(2), 214-220. http://pediatrics.aappublications.org/content/early/2011/07/21/peds.2010-3385.full.pdf.

National Institute of Allergy and Infectious Diseases. (2010). Community immunity ("herd" immunity). http://www.niaid.nih.gov/topics/pages/communityimmunity.aspx.

Reinberg, S. (2012). Measles deaths falling worldwide. HealthDay News. http://consumer.healthday.com/Article.asp?AID=664027.

Simons, E., Ferrari, M., Fricks, J., Wannemuehler, K., Anand, A., Burton, A. et al. (2012). Assessment of the 2010 global measles mortality reduction goal: results from a model of surveillance data. Lancet, DOI:10.1016/S0140-6736(12)60522-4. http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(12)60522-4/fulltext.

Measles

My beautiful bride
April 23, 2005

Seven years ago today I married my precious wife. From the moment I saw her I knew that she is a woman to be adored and I prayed that I would be the man who could spend his life loving her. She is the answer to my prayer and my treasure.

Happy anniversary Holly!

In my post last week I touched on measles vaccine effectiveness. I had already decided to write this week's post on measles before the Centers for Disease Control and Prevention (CDC) published its summary of measles in the United States, 2011.

Last year there were 222 cases of measles in the U.S. Ninety percent of those cases were either imported from other countries or linked to imported cases. More than half of the imported measles cases came from Europe, where there were over 30,000 cases of measles last year. The highest incidence of measles in Europe was in infants too young to receive the measles vaccine.

Eighty six percent of measles cases in the U.S. last year were in unvaccinated people or people whose vaccination status was unknown. Most of the unvaccinated cases were eligible to receive measles, mumps, and rubella vaccine (MMR), but 18 of those cases were children too young to receive MMR. Seventy people (32% of measles cases) were hospitalized with measles in the U.S. last year.

Measles:

Koplik spots
CDC

Measles is a highly contagious viral disease transmitted by respiratory droplets. The incubation period (time from infection to the beginning of symptoms) is 10 to 12 days. Symptoms begin with a prodrome of fever, cough, coryza (inflammation of the nasal sinuses), and conjunctivitis (red eyes). These symptoms are easily confused with other upper respiratory infections. The prodromal stage is when a person infected with the measles virus is most contagious. Koplik spots are sores on the inside of the mouth that occur during this period and are considered pathognomonic for measles – meaning, if you have Koplik spots, you have the measles.

The prodromal stage lasts 2 to 4 days and ends with the onset of a rash that begins on the head and face, spreads to the trunk, and then the arms, legs, hands, and feet. The rash fades over 3 to 4 days in the same order as it appeared; face, trunk, extremities.

Complications of measles:

In industrialized countries, around 1% to 6% of people with measles with develop pneumonia, 7% to 9% will develop otitis media (ear infection), 8% will develop diarrhea, and 1 person out of 1,000 to 2,000 will develop encephalitis as the result of the infection.

Measles can cause severe disease and death in people with immune deficiencies, including people with HIV/AIDS, people on immune-suppressing drugs (e.g., cancer chemotherapy and drugs to prevent rejection of transplanted organs), and people with inherited immune disorders. Measles vaccine should not be given to people with severe immune disorders, so this is a population that is especially vulnerable to measles.

Before the introduction of measles vaccine, there were around 200,000 to 500,000 cases of measles every year in the U.S. As a result, there were approximately 150,000 cases of pneumonia, 100,000 cases of otitis media, 4,000 cases of encephalitis, and around 500 deaths caused by measles every year in the U.S.

Globally, the number of deaths due to measles has decreased from an estimated 2.6 million in 1980 to 535,000 in 2000 and 139,000 in 2008, most of which were children in developing countries. In addition to the complication listed above, measles commonly causes diarrhea, dehydration, and blindness in children in developing countries.

Subacute Sclerosing Panencephalitis (SSPE) is a rare but fatal complication of measles. It begins years after the initial measles infection with mental and behavioral changes, then progresses to myoclonic jerking, coma, and death. Jaxon's Cure is a website that tells the story of a boy who got the measles when he was too young to receive the vaccine, developed SSPE when he was 5 years old, and died two and a half years later.

Measles vaccine:

As I discussed in my post on pertussis vaccines, antibodies are transported across the placenta from mother to baby. The same is true of measles antibodies, which provides the newborn baby with some protection against measles in the first months of life. Unfortunately, these antibodies also interfere with baby's immune response to measles vaccines, which is why measles, mumps, and rubella vaccine (MMR) is given when babies are 12 to 15 months old - after maternal measles antibodies have cleared from the baby's blood. In countries where the risk of measles is high, measles vaccine is given at 9 months.

Like live attenuated influenza vaccine (LAIV), MMR is a live virus vaccine, so it should not be given to pregnant women because of the theoretical risk of infecting the unborn baby with vaccine virus. Measles infection during pregnancy can cause miscarriage and premature delivery, so women should be up-to-date on their MMR immunization before getting pregnant.

I've reached a point where I realize that there's still a lot to discuss and this post is already longer that I had anticipated. Besides, it's time for me to make an anniversary dinner for my bride.

More information:

• CDC's Travelers' Health: Measles Update
• Jaxon's Cure: Measles and Subacute Sclerosing Panencephalitis (SSPE)

References:

Centers for Disease Control and Prevention. (1998). Measles, mumps, and rubella – vaccine use and strategies for elimination of measles, rubella, and congenital rubella syndrome and control of mumps: recommendations of the Advisory Committee on Immunization Practices (ACIP). Morbidity and Mortality Weekly Report, 47(8),1-57. http://www.cdc.gov/mmwr/preview/mmwrhtml/00053391.htm.

Centers for Disease Control and Prevention. (2012). Measles – United States, 2011. Morbidity and Mortality Weekly Report, 61(15), 253-257. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6115a1.htm.

Centers for Disease Control and Prevention. (2012). Progress in global measles control. Morbidity and Mortality Weekly Review, 61(4), 73-78. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6104a3.htm.

European Centre for Disease Prevention and Control. (2012). Surveillance report: European monthly measles monitoring. http://ecdc.europa.eu/en/publications/publications/sur_emmo_european-monthly-measles-monitoring-february-2012.pdf.

Gershon, A. A. (2009). Measles virus (rubeola). In Mandell, G. L., Bennett, J. E., & Dolin, R. (Eds.). Mandell, Douglas, and Bennett’s principles and practice of infectious diseases. (7th Ed.) [Electronic version].

National Institute of Neurological Disorders and Stroke. (2011). NINDS subacute sclerosing panencephalitis information page. http://www.ninds.nih.gov/disorders/subacute_panencephalitis/subacute_panencephalitis.htm.

Strebel, P. M., Papania, M. J., Dayan, G. H., & Halsey, N. A. (2008). Measles vaccine. In S. A. Plotkin, W. A. Orenstein, & P. A. Offit (Eds.) Vaccines (5th Ed.) [Electronic version]

World Health Organization. (2012). Measles. http://www.who.int/topics/measles/en.