Measles and Rubella Seroprevalence in a Population of Young Adult Blood Donors, France 2013

France has experienced several measles outbreaks in recent years, resulting in several deaths. Measles remains a public health threat.
The goal of jointly eliminating measles and rubella—notifiable diseases—through vaccination is enshrined in the European Vaccine Action Plan 2015–2020, adopted by WHO Europe and to which France has subscribed. In France, despite the widespread use of MMR vaccination for over 30 years, a major measles epidemic occurred between 2008 and 2012, with half of the cases occurring among young adults. Vaccination coverage is poorly understood in this population, but a seroprevalence study conducted in the general population in 2009–2010 showed insufficient immunity levels. This is why, since 2011, vaccination with two doses of the MMR vaccine has been recommended for all individuals over one year of age born since 1980.
The article published in Epidemiology and Infection presents the results of a new seroprevalence study conducted among young adults aged 18 to 32, the population targeted by this catch-up vaccination recommendation. This study is the result of a collaboration between Santé publique France, the French Blood Establishment, and the National Reference Center for Measles and Rubella.

3 questions for Denise Antona, Infectious Diseases Division

KNOWLEDGE OF VACCINATION COVERAGE FOR INFECTIOUS DISEASES, ONE OF SANTÉ PUBLIQUE FRANCE’S MISSIONS, IS ESSENTIAL FOR THE GOAL OF REDUCING OR EVEN ERADICATING INFECTIOUS DISEASES. WHY WAS A SEROPREVALENCE STUDY, FOLLOWING THE ONE IN 2010, TARGETED AT THIS POPULATION OF YOUNG ADULTS? WHAT WERE ITS OBJECTIVES?

Vaccination coverage is poorly understood among young adults. The 2010 seroprevalence study showed that it was primarily among young adults that unprotected individuals against measles and rubella were found (i.e., those with a negative serological result). The main objective of this new 2013 seroprevalence study was to reassess the level of protection against these two diseases among the population of metropolitan France as well as the overseas departments of Guadeloupe, Martinique, and Réunion. A difference was particularly expected regarding measles, following the intense circulation of the virus during the 2009–2011 epidemic that affected the entire metropolitan territory. For both diseases, the level of protection is also expected to have changed due to improved vaccination coverage following the intensification of information campaigns on measles vaccination in 2010–2011, with the use of the MMR vaccine. Furthermore, in 2011, catch-up vaccination recommendations were modified, with two doses of MMR now required for the population born after 1980. This study was also intended to provide baseline data for future monitoring of immunity among young adults against these two diseases, through the continued conduct of similar cross-sectional surveys as part of efforts to track progress toward elimination.

The second objective of this study was to estimate the incidence of measles among young adults aged 18 to 32 during the 2009–2012 epidemic in the southeastern region of France, where the virus circulated predominantly, and, based on this estimate, to be able to estimate the rate of underreporting of notifiable cases in this same population.

HOW HAS THE SUSCEPTIBILITY OF THIS POPULATION TO MEASLES AND RUBELLA CHANGED SINCE THE 2010 SEROPREVALENCE STUDY REGARDING THE GOAL OF ELIMINATING THESE TWO DISEASES?

A comparison of the results of this study with those of the 2010 seroprevalence survey shows that susceptibility to measles among the 18–32 age group has remained stable at around 9%, including in southeastern France, the region most affected by the 2011 measles epidemic. This indicates that the immunological profile of this population was affected not so much by the number of cases that occurred but primarily by a catch-up vaccination policy involving two doses of MMR, which remained insufficient to achieve a significant reduction in the number of people at risk of developing measles. In short, applying this rate to the population recorded by INSEE means that there are approximately one million people in France aged 18 to 32 who remain susceptible to contracting measles, despite being targeted by a catch-up vaccination campaign. For the record, in this age group, the target to be achieved to enable the elimination of measles is a seronegative rate of less than 5%. As for rubella, the same observation was made, with a proportion of seronegative individuals found to be virtually identical between the two surveys, except for the Southeast region, where the proportion of people susceptible to the disease decreased significantly between 2010 and 2013.

THIS STUDY ALSO HIGHLIGHTS UNDERREPORTING OF MEASLES, A NOTIFIABLE DISEASE. WHAT, THEN, WOULD BE THE ESTIMATED TOTAL NUMBER OF MEASLES CASES IN THE COUNTRY? DO THESE RESULTS CALL INTO QUESTION THE GOAL OF ELIMINATING MEASLES BY 2020?

Measles re-emerged in DO in July 2005, with biologically confirmed cases. Our study estimated the completeness of DO reporting in the Southeast subregion at 55%. Applying this rate to all age groups and other regions leads to an estimate, for example, that in 2018, more than 5,000 cases of measles actually occurred during the year, whereas only slightly more than 2,900 cases were reported. Elimination of the disease requires an incidence rate in the general population of less than 1 case per million inhabitants, which in the case of France corresponds to fewer than 67 cases per year. With more than 2,900 reported cases in 2018—and likely more than 5,000 actual cases when underreporting is taken into account—the incidence in 2018 was nearly 75 times higher than the level required for elimination. Unless vaccination coverage is rapidly improved, particularly among young adults, France will clearly not achieve the goal of eliminating measles by 2020.