This is planned more to harm than to benefit.

In this open-label, nonrandomized clinical study, we assessed the immunogenicity and safety of a fourth dose of either BNT162b2 (Pfizer–BioNTech) or mRNA-1273 (Moderna) administered 4 months after the third dose in a series of three BNT162b2 doses (ClinicalTrials.gov numbers, NCT05231005. opens in new tab and NCT05230953. opens in new tab; the protocol is available with the full text of this letter at NEJM.org). Of the 1050 eligible health care workers enrolled in the Sheba HCW COVID-19 Cohort,1,2 154 received the fourth dose of BNT162b2 and, 1 week later, 120 received mRNA-1273. For each participant, two age-matched controls were selected from the remaining eligible participants (Fig. S1 in the Supplementary Appendix, available at NEJM.org).

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