**Note: the publication below is a special advance publication of the European Congress of Clinical Microbiology and Infectious Diseases (ECCMID 2022, Lisbon, 23-26 April). Please credit congress if you use this story**

New research, to be presented at this year’s European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) in Lisbon, Portugal (April 23-26), suggests that the current two-dose measles vaccine coverage target of 95% may be the absolute minimum needed to provide sufficient protective immunity in the population to achieve and maintain measles elimination.

The systematic review and meta-analysis examining the effectiveness of two doses of the measles vaccine in over 7,000 participants (aged 9 months to 23 years) from 13 countries [1] is by Lukas Hemmers of the State Office for Health and Social Affairs in Berlin, Germany, and colleagues.

According to the latest published figures of 2018 [2]only six EU/EEG countries (Croatia, Hungary, Iceland, Portugal, Slovakia and Sweden) report two-dose measles vaccination coverage of 95% or more, suggesting that measles elimination in the EU is uncertain, researchers say.

Measles elimination is defined as the absence of endemic measles transmission in a region or other defined geographic area for 12 months or longer. Because measles spreads so easily, an estimated 95% of the population needs to be immunized with two doses of measles vaccine (MCV2) every year in every community to ensure everyone’s protection and prevent outbreaks.

This current elimination strategy assumes that two doses of measles are at least 96% effective in preventing measles and that at least 91.5% of the population is immune to the disease. However, estimates of MCV2 vaccine effectiveness have not been properly combined to determine whether they are high enough to achieve elimination.

To provide further evidence, the researchers searched for all observational studies published in English, German, Dutch and Spanish, which reported on the effectiveness of the MCV2 vaccine up to April 2021. The final analysis included 33 peer-reviewed articles. peers from an initial cache of 430. The analysis included 21 studies comparing the risk of measles in individuals (aged 9 months or older without immunodeficiency) who had received MCV2 with those who had not been vaccinated. All studies were conducted in outbreak settings.

The analysis estimated that the average efficacy of MCV2 was 96.4% in the general population under real-world conditions. Age, location and study design did not appear to impact vaccine efficacy, although moderator analysis was limited to only seven studies from Europe and North America .

“Over the past two years, the number of measles cases reported in Europe has been low, likely due to COVID-19 control measures rather than reaching the 95% immunization target for vaccination against measles. However, our analysis suggests that even if routine two-dose measles vaccination reaches 95% and vaccine efficacy is 96%, the fraction of the population that needs to be immunized to achieve elimination (i.e. i.e. 91.6%) is barely reached. , if you don’t take into account the immunity conferred by one dose of measles-containing vaccine,” says Hemmers.

He continues, “Assuming that pre-pandemic contact patterns will return upon exit from the pandemic, a vaccination level of 95% should be the minimum requirement, rather than the goal, for successful measles elimination. Therefore, further efforts to increase measles vaccination coverage are needed in most European countries.

Prior to the COVID-19 pandemic, nearly 90,000 measles cases and 37 deaths were reported in 48 out of 53 countries in the WHO European region in the first six months of 2019. This is more than the 84 462 cases recorded for the whole of 2018. Ukraine was particularly affected, with more than 54,000 cases and 18 deaths in the first six months of 2019. In addition, four countries (Albania, Czechia, Greece and United Uni) have lost their measles elimination status [3]. Across the European region, second dose measles vaccination coverage was 91% in 2018 [4].

The authors acknowledge some limitations to the study, including that the review primarily included observational studies from the WHO regions of Europe and North America. Additionally, the included studies did not provide data on people over the age of 23, which may limit the conclusions that can be drawn. “This underscores that our view of the immunogenicity of measles vaccination is biased towards younger people and that the effect of declining immunity in adults is not sufficiently considered” , says Hemmers.

For interviews with the authors of the report, please contact Lukas Hemmers, State Office for Health and Social Affairs in Berlin, Germany E) [email protected] T) +49 30 90229-2439

Alternate contact in the ECCMID press room: Tony Kirby T) + 44(0)7834 385827 E) [email protected]

Notes to Editors:

[1] United States, Germany, Canada, Romania, Spain, Austria, Bosnia and Herzegovina, Georgia, Netherlands, Ukraine, Australia, Palau, Tanzania.
[2] European Center for Disease Prevention and Control: ECDC. Measles and rubella monthly surveillance report, April 2020 – Monthly measles and rubella surveillance report – April 2020 (europa.eu)
[3]WHO/Europe | Media center – European Region losing ground in efforts to eliminate measles
[4] Measles-Situation-report-July-2019_final-2.pdf (who.int)

The authors declare no conflict of interest.

This press release is based on Oral Presentation 2556 to be made at the European Congress of Clinical Microbiology and Infectious Diseases (ECCMID). All accepted abstracts have been carefully reviewed by the conference selection committee. There is no complete article at this stage, but the authors are happy to answer your questions. The research has not yet been submitted to a medical journal for publication.

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