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Neutralising antibody responses to SARS-CoV-2 omicron among elderly upon a booster dose of BNT162b2

Full title: Neutralising antibody responses to SARS-CoV-2 omicron among elderly nursing home residents following a booster dose of BNT162b2 vaccine: A community-based, prospective, longitudinal cohort study.

Bruel T, Pinaud L, Tondeur L, Planas D, Staropoli I, Porrot F, Guivel-Benhassine F, Attia M, Pelleau S, Woudenberg T, Duru C, Koffi AD, Castelain S, Fernandes-Pellerin S, Jolly N, De Facci LP, Roux E, Ungeheuer MN, Van Der Werf S, White M, Schwartz O, Fontanet A.

Here, we show that a booster dose of the Pfizer BNT162b2 vaccine increases SARS-CoV-2 specific antibody levels and is required to elicit neutralising antibodies against omicron in the elderly population naïve to SARS-CoV-2 infection. Elderly individuals with a history of COVID-19 have higher antibody levels compared to non-convalescents, and their sera are capable of neutralising omicron already after the second dose of the primary vaccine series. Nevertheless, we observed breakthrough infections with omicron after the booster dose, more frequently in the elderly individuals with lower levels of anti-Spike antibodies and with a lower capacity to neutralise omicron.

Overall, our data show that elderly individuals are at risk of omicron infection even after a booster dose, potentially due to the considerable immune escape of this variant. Elderly individuals with previous COVID-19 infection have a stronger immune response, but their antibody levels will likely decline over time. Thus, a fourth dose of vaccine may be useful in the elderly population to further increase the level of SARS-CoV-2 specific antibodies and compensate for the waning of immunity.

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