Monday, April 23, 2012


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.


Koplik spots
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:


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.

Centers for Disease Control and Prevention. (2012). Measles – United States, 2011. Morbidity and Mortality Weekly Report, 61(15), 253-257.

Centers for Disease Control and Prevention. (2012). Progress in global measles control. Morbidity and Mortality Weekly Review, 61(4), 73-78.

European Centre for Disease Prevention and Control. (2012). Surveillance report: European monthly measles monitoring.

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.

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.

Sunday, April 15, 2012

Attack ratios

First: No vaccine is 100% effective.

For each vaccine, there is a proportion of people who will not develop immunity to the disease from the vaccine. Some vaccines are more effective than others. The effectiveness of pertussis vaccines is complicated by the fact that immunity to pertussis (whooping cough) wanes, so a person becomes more susceptible to Bordetella pertussis infection with the amount of time since the last dose of a pertussis-containing vaccine.

I know the last thing that U.S. taxpayers want to think about on April 15th is math, but I found this sentence about the 2010 pertussis epidemic in California in the news recently: "Of the 132 patients under age 18, 81 percent were up to date on recommended whooping cough shots and eight percent had never been vaccinated. The other 11 percent had received at least one shot, but not the complete series."

Does that mean that pertussis vaccine is only 19% effective? Does that mean that children who have not been vaccinated are less likely to get pertussis?

The first thing to realize is that those are percentages of cases of pertussis, not percentages of vaccinated versus unvaccinated children who got pertussis.

The question is: what is the denominator?

To know how effective a vaccine is, the denominator we need is the number of vaccinated and unvaccinated people who were exposed to a vaccine-preventable disease.

In 2010, 95% of children 19 to 35 months of age had received at least 3 doses of pertussis-containing vaccine and 68% of children 13 – 17 years of age had received a dose of tetanus, diphtheria, and acellular pertussis vaccine (Tdap). In California, 93.1% of kindergarten students had received at least 3 doses of DTP/DTaP/DT.

The reason why more vaccinated children got pertussis than unvaccinated children is that most children are vaccinated against pertussis. The percent of vaccinated children who got pertussis (attack ratio) is smaller than the percent of unvaccinated children who got pertussis.

In large outbreaks, like the California pertussis epidemic and our current pertussis epidemic in Washington State, knowing the total number of people exposed to the infecting pathogen can be difficult, so let's look at some smaller outbreaks of another vaccine-preventable disease:

There was an outbreak of measles in a high school in Utah in 1996. Of the 17 cases of measles, 8 were in students who had received measles, mumps, and rubella vaccine (MMR) and 9 were in unvaccinated children. So, 47% of cases were vaccinated students and 53% of cases were unvaccinated students.

Does that mean that the vaccine was not effective?

Not when we consider that the denominators were 852 vaccinated students and 27 unvaccinated students in the school. So, the measles attack ratio* was 1% of vaccinated students (8 ÷ 852) and 33% of unvaccinated students (9 ÷ 27).

Vaccine effectiveness (VE) is calculated as:

[(ARU – ARV) ÷ ARU] x 100

where ARU is the attack ratio in unvaccinated individuals and ARV is the attack ratio in vaccinated individuals. In the Utah outbreak, the effectiveness of MMR at preventing measles was:

[(33 – 1) ÷ 33] x 100 = 97%

This outbreak occurred before the Advisory Committee on Immunization Practices (ACIP) recommended 2 doses of MMR rather than one. None of the 72 students who had received 2 doses of MMR got the measles, so the vaccine effectiveness for 2 doses of MMR was 100%.

Similar attack ratios and vaccine effectiveness has been seen in other measles outbreaks:

In an outbreak in a German public school, the measles attack ratio was:
·       53% of unvaccinated students
·       1.4% of vaccinated students
Vaccine effectiveness was:
·       98.1% for one dose of measles-containing vaccine
·       99.4% for two doses

In a primary school in Singapore, the measles attack ratio was:
·       52.8% of unvaccinated students
·       1.2% of vaccinated students
Vaccine effectiveness was 97.8%

What about pertussis?

In an outbreak in the Virgin Islands, the attack ratio for pertussis was:
·       18% of unvaccinated students
·       6% of vaccinated students
Vaccine effectiveness was 65.6%

Among pertussis cases ages 6 months to 5 years in an outbreak in an Amish community:
·       88 (72%) had no record of pertussis immunization
·       6 (5%) had received one or two doses of DTP/DTaP
·       29 (24%) had received ≥3 doses of DTP/DTaP
We don't know the denominators for this outbreak (the number of children exposed to B. pertussis), so we can't calculate the attack ratios or vaccine effectiveness.

Obviously, pertussis vaccines are not as effective as measles vaccine, but people vaccinated against pertussis that become infected with B. pertussis less likely than people who are not vaccinated to have severe disease and less likely to transmit the bacteria to others (Baptista et al., 2006; Préziosi & Halloran, 2003).

Why use a vaccine that is not 100% effective?

Would you stop locking your doors because burglars can still break into your house when the doors are locked? Would you stop wearing a seatbelt because you can still be injured in a motor vehicle accident while you are wearing a seatbelt?

Seatbelts reduce the risk serious injuries.

Locked doors reduce the risk of being robbed.

Vaccines reduce the risk of vaccine-preventable diseases.

Please drive carefully.
Road Crash Fatalities on US Income Tax Days

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*The term "attack rate" is commonly used, but a rate is an incidence over time.


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. (1997). Measles outbreak, southwestern Utah, 1996. Morbidity and Mortality Weekly Report, 46(33), 766-769.

Centers for Disease Control and Prevention. (1998). Measles, mumps, and rubella – vaccine use and strategies for elimination of measles, mumps, 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.

Centers for Disease Control and Prevention. (2006). Pertussis outbreak in an Amish community – Kent County, Delaware, September 2004 – February 2005. Morbidity and Mortality Weekly Report, 55(30), 817-821.

Centers for Disease Control and Prevention. (2011). National and state vaccination coverage among adolescents aged 13 through 17 years – United States, 2010. Morbidity and Mortality Weekly Report, 60(33),1117-1123.

Centers for Disease Control and Prevention. (2011). National and state vaccination coverage among children aged 19 – 35 months – United States, 2010. Morbidity and Mortality Weekly Report, 60(34), 1157-1163.

Centers for Disease Control and Prevention. (2011). Vaccination coverage among children in Kindergarten – United States, 2009 – 2010 school year. Morbidity and Mortality Weekly Report, 60(21), 700-704.

Grens, K. (April 3, 2012). Whooping cough vaccine fades in pre-teens: study. Reuters Health Information. Retrieved April 14, 2012 from

Ong, G., Rasidah, N., Wan, S., & Cutter, J. (2007). Outbreak of measles in primary school students with high first dose MMR vaccination coverage. Singapore Medical Journal, 48(7), 656-661.

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

Wei, S. C., Tatti, K., Cushing, K., Rosen, J., Brown, K., Cassiday, P., Clark, T. et al. (2010). Effectiveness of adolescent and adult tetanus, reduced-dose diphtheria, and acellular pertussis vaccine against pertussis. Clinical Infectious Diseases, 51(3), 315-321.

Wichmann, O., Hellenbrand, W. Sagebiel, D., Santibanez, S., Ahlemeyer, G., Vogt, G. et al. (2007). Large measles outbreak at a German public school, 2006. Pediatric Infectious Disease Journal, 26(9), 782-786.

Saturday, April 7, 2012

Pertussis epidemic, Washington State

I've been working on our tax return today and will be spending Easter Sunday with Holly's parents, so I'm going to keep this week's post short.

Tuesday the Washington State Secretary of Health Mary Selecky announced that the incidence of pertussis has reached epidemic levels in Washington. There have been 640 cases since January 1st, compared to 94 cases by this time last year.

For those who have not yet received a Tdap, many pharmacies now offer immunization: Adult Vaccination Locator

Happy Easter!

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