Protection of Covid-19 vaccinantion and Omicron

Backgrounds

Knowing the duration of effectiveness of COVID-19 booster doses is essential to provide decision makers with scientific arguments about the frequency of subsequent injections. We estimated the level of protection against COVID-19-related-hospitalisations (Omicron BA.4-BA.5) over time after vaccination, accounting for breakthrough infections.

Methods

In this nationwide case-control study, all cases of hospitalisations for COVID-19 identified in the comprehensive French National Health Data System between 06/01/2022 and 10/15/2022 were matched with up to 10 controls by year of birth, sex, department, and an individual COVID-19 hospitalisation risk score. Conditional logistic regressions were used to estimate the level of protection against COVID-19-related-hospitalisations conferred by primary and booster vaccination, accounting for history of SARS-COV-2 infection.

Results

38,839 cases were matched to 377,653 controls. 19.2% and 9.9% were unvaccinated, respectively, while 68.2% and 77.7% had received ≥1 booster dose. Protection provided by primary vaccination reached 45%[42%; 47%]. The incremental effectiveness of booster doses ranged from 69%[67%; 71%] (≤2 months) to 22%[19%; 25%] (≥6 months). Specifically, the second booster provided an additional protection compared with the first ranging from 61%[59%; 64%] (≤2 months) to 7%[2%; 13%] (≥4 months). Previous SARS-COV-2 infection conferred a strong, long-lasting protection (51% ≥ 20 months). There was no incremental effectiveness of a second booster among individuals infected since the first booster.

Conclusion

In the era of Omicron BA.4 and BA.5 predominance, primary vaccination still conferred protection against COVID-19 hospitalisation, while booster doses provided an additional time-limited protection. The second booster had no additional protection in case of infection since the first booster.

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