Happy birthday Andrew!
Our little boy is two years old today. Seeing Andrew grow up has been one of the greatest joys of my life. I have been enthralled by watching our little scientist learn about the world. Watching him learn new skills and challenge himself has made me a very proud daddy!
Measles vaccine is highly effective; so effective that high immunization coverage has resulted in the elimination of measles from the U.S. Nevertheless, a small proportion of people who receive measles vaccine do not develop an immune response sufficient to prevent infection. This is known as primary vaccine failure. There is evidence that measles antibody levels (titers) wane over time allowing some people to become susceptible to measles. Infection in a person who initially developed an adequate immune response to the vaccine but later became susceptible is called secondary vaccine failure.
One of the factors that contributes to waning immunity to measles is the loss of natural boosting. In the past, people in the U.S. were periodically exposed to measles virus during epidemics. Since measles has been eliminated from the U.S., exposure to the virus in this country has become rare.
Secondary measles vaccine failure is more likely to occur with intense exposure to the measles virus. This can occur during an outbreak or among household contacts of a person with measles. For this reason, it's not unusual to find vaccinated people with measles during an outbreak.
Modified measles, measles in a vaccinated person, is much milder than measles in an unvaccinated person; fever and rash are less severe and a person with modified measles is much less likely to develop complications of measles than an unvaccinated person with measles. In contrast to unvaccinated people with measles, vaccinated people who develop modified measles have high avidity antibodies, meaning, their antibodies are mature and bind tightly to the virus.
People with modified measles are also much less likely to infect other people than unvaccinated people with measles. There have been numerous cases of modified measles in previously vaccinated people with no evidence of transmission to close contacts reported in the medical literature. There have even been reports of vaccinated doctors who developed modified measles but did not infect their patients (Lee et al., 2008; Rota et al., 2011).
Earlier this year, Jennifer Rosen and colleagues published the first report of transmission of measles from a previously vaccinated person. In 2011, a 22-year-old woman in New York City who had received two doses of MMR as a child who developed measles. Out of 88 people who had contact with her, 4 people developed measles. One was her coworker and the other three were health care workers at a clinic. Two of the secondary cases had received two doses of MMR as children and the other two had previous evidence of immunity (positive immunoglobulin G titer). None of the contacts to the four secondary cases developed measles. The authors wrote, "this outbreak probably represents a series of rare events" and that it "does not justify a change in current measles control and elimination strategies."
Centers for Disease Control and Prevention. (2013). Prevention of measles, rubella, congenital rubella syndrome, and mumps, 2013: summary recommendations of the Advisory Committee on Immunization Practices (ACIP). Morbidity and Mortality Weekly Report, 62(4), 1-34. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr6204a1.htm.
Gershon, A. A. (2009). Measles virus (rubeola). In G. L. Mandell, J. E. Bennett, & R. Dolin (Eds.). Mandell, Douglas, and Bennett’s principles and practice of infectious diseases. (7th Ed.) [Electronic version].
Hickman, C. J., Hyde, T. B., Sowers, S. B., Mercader, S., McGrew, M., Williams, N. J. et al. (2011). Laboratory characterization of measles virus infection in previously vaccinated and unvaccinated individuals. Journal of Infectious Diseases, 204(Suppl. 1), S549-S558. http://jid.oxfordjournals.org/content/204/suppl_1/S549.full.
Lee, N. Y., Lee, H. C., Chang, C. M., Wu, C. J., Ko, N. Y., Ko, C. (2008). Modified measles in a healthcare worker after return from travel. Infection Control and Hospital Epidemiology, 29(4), 380-381. http://www.jstor.org/stable/10.1086/529031.
Mercader, S., Garcia, P., & Bellini, W. J. (2012). Measles virus avidity assay for use in classification of measles vaccine failure in measles elimination settings. Clinical and Vaccine Immunology, 19(11), 1810-1817. http://cvi.asm.org/content/19/11/1810.
Mitchell, P., Turner, N., Jennings, L., & Dong, H. (2013). Previous vaccination modifies both the clinical disease and immunological features in children with measles. Journal of Primary Health Care, 5(2), 93-98. http://www.ncbi.nlm.nih.gov/pubmed/23748389.
Rosen, J. B., Rota, J. S., Hickman, C. J., Sowers, S. B., Mercader, S., Rota, P. A. et al. (2014). Outbreak of measles among persons with prior evidence of immunity, New York City, 2011. Clinical Infectious Diseases, 58(9), 1205-1210. http://cid.oxfordjournals.org/content/early/2014/02/27/cid.ciu105.
Rota, J. S., Hickman, C. J., Sowers, S. B., Rota, P. A., Mercader, S., & Bellini, W. J. (2011). Two case studies of modified measles in vaccinated physicians exposed to primary measles cases: high risk of infection but low risk of transmission. Journal of Infectious Diseases, 204(Suppl. 1), S559-S563. http://jid.oxfordjournals.org/content/204/suppl_1/S559.full.