Analysis compares the efficacy of hybrid immunity and vaccination against reinfection in various demographics.
Background The evolution of the magnitude of the impact from 2020 to 2024 of prevention measures (vaccination and natural immunity) against covid-19 reinfection in daily practice on the population is not known. Objective To compare the number needed to treat (NNT) and the number needed to harm (NNH) for SARS-CoV-2 reinfections, associated with prevention measures (mainly acquired immunity through vaccination and natural immunity), since 2020-2022 period to 2023 vs. 2023 to 2024. Methodology Comparison of secondary data among covid-19 reinfection cases in 2020-2022 period to 2023 vs. 2023 to 2024 of previous studies. For the calculation of NNT and NNH of SARS-CoV-2 infections, cases in 2020-2022 period were considered control group with respect to cases in 2023, and cases in 2023 were considered control group with respect to cases in 2024. Results Lower NNT figures (greater magnitude of the hybrid immunity effect) and higher NNH figures (lower risk of harm with hybrid immunity) were found since the period 2020-2022 to 2023 versus 2024. 2023 to 2024. Since 2020-2022 period to 2023 the lowest NNT figures were for women (17) and People with some type of labor specialization (59). And the highest NNH figures were for men (1000) and Moderate-severe severity of reinfection (500). Since 2023 to 2024 the lowest NNT figures were Socio-Health Care Workers (5) and Complex families (111). And the highest NNH figures were for population >14 years (500) and People with some type of labor specialization (333). Conclusion In the context of this general practice setting in Toledo, Spain, there was a lower magnitude of the beneficial effect of hybrid immunity from 2023 to 2024 vs. from 2020-2022 to 2023. In any case, the greatest benefit in 2024 is for Socio-Health Care Workers and the least harm is for the population >14 years old.
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José Luis Turabián (2025) studied this question.
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