A single dose of the SARS-CoV-2 vaccine BNT162b2 elicits Fc-mediated antibody effector functions and T-cell responses

Tauzin, Alexandra; Nayrac, Manon; Benlarbi, Mehdi; Gong, Shang Yu; Gasser, Romain; Beaudoin-Bussières, Guillaume; Brassard, Nathalie; Laumaea, Annemarie; Vézina, Dani; Prévost, Jérémie; Anand, Sai Priya; Bourassa, Catherine; Gendron-Lepage, Gabrielle; Medjahed, Halima; Goyette, Guillaume; Niessl, Julia; Tastet, Olivier; Gokool, Laurie; Morrisseau, Chantal; Arlotto, Pascale; Stamatatos, Leonidas; McGuire, Andrew T.; Larochelle, Catherine; Uchil, Pradeep; Lu, Maolin; Mothes, Walther; De Serres, Gaston; Moreira, Sandrine; Roger, Michel; Richard, Jonathan; Martel-Laferrière, Valérie; Duerr, Ralf; Tremblay, Cécile; Kaufmann, Daniel E.; Finzi, Andrés

While the standard regimen of the BNT162b2 mRNA vaccine for SARS-CoV-2 includes two doses administered three weeks apart, some public health authorities are spacing these doses, raising concerns about efficacy. However, data indicate that a single dose can be up to 90% effective starting 14 days post administration. To assess the mechanisms contributing to protection, we analyzed humoral and T cell responses three weeks after a single BNT162b2 dose. We observed weak neutralizing activity elicited in SARS-CoV-2 naïve individuals but strong anti-receptor binding domain and Spike antibodies with Fc-mediated effector functions and cellular CD4+ T cell responses. In previously-infected individuals, a single dose boosted all humoral and T-cell responses, with strong correlations between T helper and antibody immunity. Our results highlight the potential role of Fc-mediated effector functions and T-cell responses in vaccine efficacy. They also provide support for spacing doses to vaccinate more individuals in conditions of vaccine scarcity.