Evaluation of the IgG and IgM Antibodies Specific for Measles Virus among Children Post-Measles Vaccination in Aden-Yemen

Background: Measles is considered a serious problem in underdeveloped nations and can only be eradicated through extensive immunization campaigns. Age at vaccination is the primary known risk factor for primary vaccine failure because it interferes with the effectiveness of the measles immunization due to the persistence of maternal antibodies. In Yemen, measles remains a serious issue even with high vaccination rates.
Objectives: The aim of this study was to determine the level of specific anti-measles virus antibodies (IgM and IgG) in response to measles vaccination among children in Aden governorate, Yemen.
Subjects and Methods: The subjects of the study were children aged 1 up to 10 years, obtained from primary health care centers at Aden-Governorate. The type of study was a cross-sectional study conducted from the 1st of January up to the end of March 2024.This involves quantifying antibody titers at various time points following vaccination to assess the vaccine's ability to induce an immune response.
Results: Out of 125 children participated in the study, the mean age of 4 years & 4 months± 2 years & 6 months of standard deviation (i.e., 4.4±2.6 SD), with the minimum age being 1 year and the maximum age being 10 years. The seroprevalence of infected children with measles virus during this study was 25 out of 125 (20%). Moreover, infected children were higher at ages 1–1.5 and 6–10 years old (46.2%, 20.4%), respectively, without a statistically significant difference (P = 0.7). The male children are more susceptible to measles infection compared to females (21.7% vs. 16.7%), respectively, without a statistically significant difference (P = 0.5). The seroprevalence of measles antibodies among the healthy vaccinated children was 80%; it was lowered than the herd immunity against measles to be achieved (90-95%) after the first & second doses. The seronegative IgG response represented 32.8%, while the seropositivity of IgG was 67.2% after the first & second doses. The seropositive IgG response tends to be high (68.8%) after 1-2 years following the 2nd dose and tends to decrease after ≥7 years old (37.5%). Moreover, the seronegative response of IgG was higher with increasing the time elapse between the 2nd dose and the serodiagnosis (62.5%), but there was no statistically significant association (P = 0.5). The means titers of IgG and IgM post-measles vaccination were different with a highly statistically significant association; t(124)=19.415, P<0.05.
Conclusion: The Measles vaccine is effective to induce protection against measles outbreaks, but there is a decline of post-vaccination measles-specific antibodies (IgG). Moreover, it has not reached the normal threshold of protection in Aden Governorate.