MONDAY, Jan. 24, 2022 (HealthDay News) — For health care workers who received a priming dose of the Ad26.COV2.S vaccine, Ad26.COV2.S and mRNA boosters are immunogenic, with the strongest responses after boosting with an mRNA-based vaccine, according to a study published online Jan. 19 in the New England Journal of Medicine.

Roos S.G. Sablerolles, M.D., from the Erasmus University Medical Center in Rotterdam, Netherlands, and colleagues conducted a single-blind, multicenter, randomized, controlled trial involving health care workers who received a priming dose of the Ad26.COV2.S vaccine. Immunogenicity and reactogenicity were assessed 28 days after receipt of no booster, an Ad26.COV2.S booster, an mRNA-1273 booster, or a BNT162b2 booster.

The researchers found that compared with a single Ad26.COV2.S vaccination, homologous or heterologous booster vaccination in 434 participants yielded higher levels of S-specific binding antibodies, neutralizing antibodies, and T-cell responses. Compared with the homologous booster, heterologous regimens that included mRNA-based vaccines resulted in a significantly larger increase in binding antibodies. The most immunogenic was the mRNA-1273 booster, which was associated with higher reactogenicity than the BNT162b2 and Ad26.COV2.S boosters. In the first two days after booster administration, local and systemic reactions were generally mild to moderate.

“Single-shot Ad26.COV2.S vaccination adequately primes the immune system,” the authors write. “We found that in the face of waning immunity and circulation of severe acute respiratory syndrome coronavirus 2 variants, these responses were boosted most efficiently with mRNA-based vaccines.”

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