Measles seroprevalence national survey among a sample of the Tunisian population: is there an explanation for the 2019 measles epidemic in a mostly vaccinated population?
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National Observatory of New and Emerging Diseases, Sfax, Tunisia
National Observatory of New and Emerging Disease, Tunis, Tunisia
National Observatory of New and Emerging Diseases, Béja, Tunisia
National Observatory of New and Emerging Diseases, Tunis, Tunisia
Department of Microbiology and Biochemistry, Hopital Aziza Othmana, Tunis, Tunisia
Observatoire National des Maladies Nouvelles et Émergeantes, Tunis, Tunisia
Publication date: 2023-04-27
Popul. Med. 2023;5(Supplement):A240
In Tunisia, the measles vaccine is included in the national-immunization-programme. An outbreak of measles occured with 3896 notified cases and 39 deaths in 2019. We conducted this study to estimate measles IgG-antibodies seroprevalence before the occurrence of 2019-outbreak. We conducted a national seroprevalence survey of measles immunity using blood samples serotheque collected during the 2014-2015 National Viral Hepatitis cross-sectional survey. Written informed consent for using the sera for further analysis was obtained from participants (parents for minors). A subsample of 3500 individuals was included based on expected seroprevalence of 85%, a precision of 0.2% and 95%CI. ELISA was used to detect IgG antibodies against measles. Participants with serum positive for measles antibody were considered protected or immune to measles disease. From 3454 serum samples tested , 3279 were positive for measles IgG antibodies, representing a seroprevalence of 94.9% (95%CI: 94.3%-95.6%). Seroprevalence was significantly lower in rural area(p<0.001). The prevalence of measles IgG antibodies was different by age(p<0.001). The seroprevalence among children aged 0-5 years was 94.7%. It was 96% for both 5-10- and 10–15-year-old populations. However, it declined significantly among 20-30 years population, 1982-1997 birth cohort, with a seroprevalence of 83.2% (95%CI: 79.7%-86.1%). Among 40-50, 50-60 and >60-year-old populations, seroprevalences were to 98.1%, 99.2%, and 98.6% respectively. In this context, during 2021, the Tunisian government, provided and recommended getting a booster dose targeting adults born between 1982-1997(20-30 years), and advancing the first dose for children from 12 to 9 months, in order to ensure a sufficient immunization rate. This study, a pre-epidemic measles seroprevalence survey, showed that seroprevalence among vaccinated population aged 20-30 years in Tunisia was low. To prevent future outbreaks, a nationwide-vaccination-campaign was implemented in 2021, aiming to boost immunity against measles. It was delayed for 2022, as a consequence of the Covid-19 pandemic.