Molecular and serological investigation of the 2021 COVID-19 case surge in Mongolian vaccinees (preprint)

ABSTRACT

A surge in Covid-19 cases in Mongolia in March 2021 resulted in a government-mandated shutdown. This shutdown was relaxed in May 2021 as case numbers decreased and nationwide vaccination rates using Sinopharm, Covishield/AstraZeneca, Sputnik V, and Pfizer/BioNTech vaccines exceeded 50% of the population. Case rates increased again in early June 2021 in both vaccinated and non-vaccinated individuals. To determine whether the surge was due to the emergence of Delta or another variant, or vaccine failure, a rapid, opportunistic investigation was conducted that comprised virus sequence analysis of nasal swab samples from breakthrough cases and antibody assays of plasma from healthy vaccinees. More than 90% of breakthrough infections during the second case surge were due to the Alpha variant. Spike protein ELISA and SARS-CoV-2 neutralization assays data revealed large differences in plasma titers of antibodies to SARS-CoV-2, with mRNA vaccines eliciting higher titers than adenovirus-vectored or killed virus vaccines.