Dynamic Features of Herd Immunity: Similarities in Age-Specific Anti-Measles Seroprevalence Data between Two Countries of Different Epidemiological History

Abstract

(1) Background: Measles immunization gap(s) raise the concern of potential outbreaks. Both Croatia and Hungary are situated in the vicinity of measles-endemic countries. Potentially compromised immunization activities due to the COVID-19 surge is a ground for concern. Our aim was to compare age-stratified seroprevalence results in the cross-border region. (2) Methods: Anti-MMR specific antibody levels (IgG) of 950 anonymous Croatian samples were compared with previous Hungarian results (n > 3500 samples), and former Croatian seroprevalence data (n = 1205). Seropositivity ratios were determined using our self-developed anti-MMR indirect ELISA (Euroimmun IgG ELISA kits were used as control). (3) Results: Measured seropositivity ratios of the Croatian samples were largely overlapping with our earlier published Hungarian data (the lowest seropositivity ratios were measured among individuals of 34–43 years of age with 78% of seropositivity) and are in accordance with earlier published data of Croatian researchers. (4) Conclusion: Although the epidemiological histories of the two countries are different, analogies in age-specific measles susceptibility have been discovered. We suggest that besides the potential coincidence in vaccination ineffectiveness, the inherent biological dynamics of vaccination-based humoral protection might have also contributed to the experienced similarities. Our findings may also serve as a lesson regarding the current anti-COVID-19 vaccination strategy.

Raising Epidemiological Awareness: Assessment of Measles/MMR Susceptibility in Highly Vaccinated Clusters within the Hungarian and Croatian Population—A Sero-Surveillance Analysis

“…This demographic cluster likely experienced natural infections either during the early stages of vaccination or before widespread vaccination efforts were implemented. Our observation aligns with the established literature suggesting that immune protection resulting from wild-type infection elicits a more durable and robust immune response compared to vaccine-induced immunity [35,66,69,70,[80][81][82][83][84][85].…”

“…The conspicuous deficit in humoral antibody titers and subsequent existence of seropositivity gaps within this age cohort prompt inquiries into vaccine efficacy [24,30,37,[69][70][71][72][73][74][75][76][77][78][79][80][81][82][83]. These findings echo previous studies [35,66,67,[69][70][71] and data in the literature [72][73][74][75][76][77][78][79], indicating persistent challenges in achieving sufficient immunity against measles despite vaccination efforts.…”

“…However, the current surge in cases diverges from historical outbreaks characterized by periodic fluctuations prior to widespread vaccination efforts. Notably, these contemporary outbreaks also occur within populations boasting high vaccination coverage [3,8,[24][25][26][27][28][29][30][31][32][33][34][35], leading to potential confusion among the public and presenting challenges for healthcare professionals, epidemiologists, and clinical microbiologists [33]. While the prevalence of vaccination among individuals significantly exceeds that of those who are unvaccinated, there appears to be a subset within the well-immunized cohort that may remain susceptible to unexpected infections, potentially introduced through imported cases such as unvaccinated travelers.…”

“…While the prevalence of vaccination among individuals significantly exceeds that of those who are unvaccinated, there appears to be a subset within the well-immunized cohort that may remain susceptible to unexpected infections, potentially introduced through imported cases such as unvaccinated travelers. Consequently, even a minor proportion of vaccinated individuals, encompassing also the aforementioned immunization gaps contracting the virus, could contribute substantially to the overall case count [32][33][34][35].…”

Measles Vaccination and Outbreaks in Croatia from 2001 to 2019; A Comparative Study to Other European Countries

“…Recently, in the study conducted in the frame of the CABCOS3 project, it was reported that the Hungarian serum samples and Croatian serum samples were largely overlapping in seropositivity ratios, which might be attributed to the intrinsic biological dynamics of vaccination-based humoral immunity to measles. Individuals 34–43 years old had the lowest seropositivity ratios (78%) [ 34 ]. A prospective study conducted in Prague, Czechia, on a total of 2782 participants aged 19–89 years, analyzed the level of measles-specific antibodies in serum samples and showed that the seropositivity rate in naturally immunized participants (before 54 years) was significantly higher than in fully vaccinated persons aged 19–48 (98.0% (95% CI: 96.5–99.0%) vs. 93.7% (95% CI: 92.4–94.9%)).…”