Low neutralizing antibody titers against the Mu variant of SARS-CoV-2 in BNT162b2 vaccinated individuals

Background Global surveillance programs for the virus that causes COVID-19 are showing the emergence of variants with mutations in the Spike protein, including the Mu variant, recently declared as a Variant of Interest (VOI) by the World Health Organization. Because these types of variants can be more infectious or less susceptible to antiviral treatments and vaccine-induced antibodies. Objectives To evaluate the sensitivity of the Mu variant (B.1.621) to neutralizing antibodies induced by the BNT162b2 vaccine. Study design Three of the most predominant SARS-CoV-2 variants in Colombia during the epidemiological peaks of 2021 were isolated. Microneutralization assays were performed by incubating 120 TCDI50 of each SARS-CoV-2 isolate with five 2-fold serial dilutions of sera from 14 BNT162b2 vaccinated volunteers. The MN50 titer was calculated by the Reed-Muench formula Results The three isolated variants were Mu, a Variant of Interest (VOI), Gamma, a variant of concern (VOC), and B.1.111 that lacks genetic markers associated with greater virulence. At the end of August, the Mu and Gamma variants were widely distributed in Colombia. Mu was predominant (49%), followed by Gamma (25%). In contrast, B.1.111 became almost undetectable. The evaluation of neutralizing antibodies suggests that patients vaccinated with BNT162-2 generate neutralizing antibody titers against the Mu variant at significantly lower concentrations relative to B.1.111 and Gamma. Conclusions This study shows the importance of continuing with surveillance programs of emerging variants as well as the need to evaluate the neutralizing antibody response induced by other vaccines circulating in the country against Mu and other variants with high epidemiological impact.