Post-COVID-19 era sero-surveillance of anti-measles IgM and IgG antibodies among asymptomatic Tanzanian children aged 3 to 15 years Journal

Abstract

In July 2022, during the COVID-19 era, Tanzania reported over 1500 laboratory-confirmed measles cases and more than 30 deaths, with about 80% of the children not vaccinated. The response was an intensive vaccination campaign that targeted under-fives across the country. This was a cross-sectional measles-serosurveillance study conducted in 2024, after the COVID-19 era, in Dar es Salaam. The study involved children aged 3 to 15 years who were attending Temeke Regional Referral Hospital (TRRH) in Dar es Salaam, Tanzania, during the study period. Children were screened for anti-measles IgM and IgG antibodies using the NovaLisa Measles ELISA kit (NovaTec Immunodiagnostica GmbH® kit) and were categorized into four groups: (i) immune to measles (presence of anti-measles virus IgG and absence of anti-measles virus IgM), (ii) having reactivated measles (presence of both anti-measles virus IgG and anti-measles virus IgM), (iii) recently contracted measles (absence of anti-measles virus IgG and presence of IgM), and (iv) vulnerable (absence of both anti-measles virus IgG and anti-measles virus IgM). Of the 155 collected blood samples, 32 (20.64%) were positive for IgM, 35 (22.58%) cases were IgG-positive, and 74 (47.74%) had both IgM and IgG anti-measles antibodies. Based on these results, 35 (22.58%) children were determined to be immune, 74 (47.74%) were adjudged to have reactivated measles, 32 (20.64%) had recently contracted measles, and 14 (9.03%) were susceptible to measles infection. We found no significant association between gender, parents' education or income, frequency of facility visits, parents' knowledge of measles, and the presence of measles symptoms with IgM and IgG antibodies. The only significant association was age and IgM, being highest (22.58%) in children aged 3-5 years (P = 0.014), indicating risk of contracting measles in early childhood. This study provides an update regarding the current immunity status of children against measles infection in the post-COVID-19 era. Our study clearly indicates a need to improve measles immunization activities and strategies. The Government of Tanzania, through the Ministry of Health, should work together with international agencies such as the World Health Organization (WHO) and United Nations International Children's Emergency Fund (UNICEF) and other stakeholders to ramp up efforts to meet the target of 95% vaccination coverage.

Keywords: Children; IgG; IgM; Measles; Seroprevalence; Tanzania.