With the implementation of the WHO strategic plan for the elimination of measles, the number of measles cases in European Region has decreased. However, outbreaks are still observed. Although most measles cases affect unvaccinated individuals, cases with vaccinated persons are also reported. Furthermore, it was described that a high percentage of young people in Poland exhibit no presence of anti-MeV IgG despite the high level of vaccination covering no less than 97% of the Polish population. Strong evidence exists that immunity to measles is complex and depends on both the humoral and cellular response and although antibodies have been used as correlates of immunity, it is increasingly being considered that antibody-based definitions of vaccine success or failure may be incomplete.
Here, we investigated immunity to measles as the reactivity of CD4 T cells to stimulation with vaccine as well as wild strains of measles virus (MeV) isolated in Poland, in young vaccinated persons and subjects infected naturally. Evidence for the presence of MeV-specific memory cells years after infection or vaccination was found, however the cells of vaccinees and naturally infected subjects reacted differently in contact with wild and vaccine MeV strains. Furthermore, the presence of a significant proportion of non-responder vaccinees was observed. In conclusion, our results may have implications for studies on the monitoring of the complexity of post-vaccine immune response.