An extended interval between vaccination and infection enhances hybrid immunity against SARS-CoV-2 variants.

Abstract

As the COVID-19 pandemic continues, long-term immunity against SARS-CoV-2 will be globally important. Official weekly cases have not dropped below 2 million since September of 2020, and continued emergence of novel variants have created a moving target for our immune systems and public health alike. The temporal aspects of COVID-19 immunity, particularly from repeated vaccination and infection, are less well understood than short-term vaccine efficacy. In this study, we explore the impact of combined vaccination and infection, also known as hybrid immunity, and the timing thereof on the quality and quantity of antibodies elicited in a cohort of 96 health care workers. We find robust neutralizing antibody responses among those with hybrid immunity against all variants, including Omicron BA.2, and significantly improved neutralizing titers with longer vaccine-infection intervals up to 400 days. These results indicate that anti-SARS-CoV-2 antibody responses undergo continual maturation following primary exposure by either vaccination or infection for at least 400 days after last antigen exposure. We show that neutralizing antibody responses improved upon secondary boosting with greater potency seen after extended intervals. Our findings may also extend to booster vaccine doses, a critical consideration in future vaccine campaign strategies.