MMR Vaccine Most Effective Against Measles but May Wane Over Time: Lancet Public Health
Between 2011 and 2019, the proportion of measles cases in adults who received two doses of the MMR vaccine in England increased from 1.9% (20/1064) to 7.2% (57/790), however, the cause of this increase remains unclear.
A new retrospective modeling study, published in The Lancet Public Health journal, suggests slow MMR vaccine waning may partially contribute to rising measles cases in double-vaccinated people when outbreaks occur. However, the study authors emphasize that the MMR vaccine remains the most effective measure to prevent measles infection and that community vaccination levels above 95% are essential to prevent outbreaks in the first place.
This study is the first to use mathematical modeling to suggest measles cases and spread in England are consistent with a small amount of waning of vaccine-induced immunity.
- No vaccine waning immunity.
- Waning of immunity increases each year from the age of five (as most vaccinated individuals have received their second dose by then).
- Individuals vaccinated before 2000 have full protection until 2000 (when measles was considered no longer endemic in England) but waning of immunity increases each year from the age of five after 2000. In this scenario, immunity in younger groups generally comes only from vaccination, rather than from vaccination and exposure to the virus.
People who have been vaccinated remain highly protected from measles. In the rare cases of a vaccinated person becoming infected with measles, previous research suggests their symptoms would likely be milder than people who have not received a vaccine, but they could still transmit the virus - in this study, the risk of onward transmission from rare cases of measles among vaccinated individuals was 83% that of unvaccinated individuals.
Reference: Funk, S., Knapp, J.K., Lebo, E. et al. Combining serological and contact data to derive target immunity levels for achieving and maintaining measles elimination. BMC Med 17, 180 (2019). https://doi.org/10.1186/s12916-019-1413-7
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