Seventy individuals who had received 1 or more doses of measles-containing vaccine transmitted measles virus, resulting in 237 secondary cases.
…91% (30/33) of studies provided data on subsequent transmission generations, leading to 812 measles cases traced back to vaccinated individuals…
Immunity following measles vaccination is similar to immunity from infection, but the antibody response is lower in magnitude and is not always lifelong. While a decrease in antibody concentration over time is normal after infection or vaccination, this process may be accelerated for measles in elimination settings due to a lack of immunological boosting from circulating virus. This may result in immune individuals becoming susceptible to measles over time, a phenomenon known as secondary vaccine failure.
[W]e conducted a systematic review of the literature to search for evidence of measles virus transmission from vaccinated cases, understand the characteristics of these cases, and the contribution of these cases to
outbreak size. We also sought to explore measures for measles vaccine effectiveness against transmission.
Across the 33 included studies, there were a total of 70 vaccinated individuals who were reported to have transmitted measles virus to others. Of these, 22 (31.4%) had been vaccinated with ≥2 doses of [measles containing vaccine].
…the median age was 16 years old.
There was no statistically significant difference in the median number of transmissions from vaccinated cases between individuals who received 1- or 2-doses.
Only one study estimated vaccine effectiveness (VE) against infectiousness. Using case surveillance data in The Netherlands, the study compared vaccinated cases that transmitted measles compared to vaccinated cases that did not and estimated a VE against infectiousness by vaccine doses. Adjusting for age group,
the study reported a VE against measles infectiousness of 10% for one dose of vaccine and 61% for at least two vaccine doses.
[O]ur review demonstrates that vaccinated cases can transmit measles virus to others in a variety of settings and circumstances…
Those who transmitted had received one to three doses of [measles containing vaccine]. Transmissions occurred in healthcare facilities, schools, and various community settings, where children who are not vaccinated or immunocompromised individuals may be focused, potentially raising the risk of transmission. The exposure times varied by study but included instances in settings where exposure was limited to brief encounters and/or no direct contact.
We hypothesize that our finding of 70 vaccinated transmitters is likely an underestimate, since not all outbreak investigations record measles vaccination history.
Additionally, since genotyping of measles virus is not always conducted in outbreaks, we cannot be certain on chains of transmission and are relying on the conclusions drawn by authors of the included papers.