# Post-pandemic changes in population immunity have reduced the likelihood of emergence of zoonotic coronaviruses

## TL;DR

Population immunity from SARS-CoV-2 and vaccines has reduced the chances of new coronaviruses emerging in humans.

## Contribution

The study shows how cross-immunity from SARS-CoV-2 reduces the likelihood of new sarbecovirus emergence.

## Key findings

- Sera from individuals with prior SARS-CoV-2 exposure showed cross-neutralizing antibodies against multiple sarbecoviruses.
- Population cross-immunity significantly reduces the likelihood of a novel sarbecovirus emerging.
- Highly specific SARS-CoV-2 vaccines may increase the risk of new virus emergence by reducing natural cross-protection.

## Abstract

Infections by endemic viruses, and the vaccines used to control them, often provide cross-protection against related viruses, potentially altering the transmission dynamics and likelihood of emergence of new zoonotic viruses with pandemic potential. Here, we investigate how population immunity after the COVID-19 pandemic has impacted the likelihood of emergence of a novel sarbecovirus, termed SARS-CoV-X. To this end, we combined empirical cross-neutralisation data with mathematical modelling to identify key immunological and epidemiological factors shaping sarbecovirus emergence. We show that sera from individuals with different COVID-19 immunological histories contained cross-neutralising antibodies against the spike (S) protein of multiple zoonotic sarbecoviruses. Simulations parameterised by these data predict that the likelihood of emergence of a novel sarbecovirus has been reduced significantly by population cross-immunity, with outcomes determined by the extent of cross-protection and R0 of the novel virus. Preventative vaccination against SARS-CoV-X using available COVID-19 vaccines can help resist emergence even in the presence of co-circulating SARS-CoV-2. However, a theoretical vaccine with high specificity to SARS-CoV-2 can increase emergence probability by suppressing SARS-CoV-2 prevalence and, by extension, levels of natural cross-protection. Overall, SARS-CoV-2 circulation and vaccination have generated widespread immunity against related sarbecoviruses, creating an immunological barrier to novel sarbecovirus emergence in humans.

Population immunity to SARS-CoV-2 may alter the epidemic potential of a novel coronavirus through cross-protection. Here, the authors investigate the extent of cross-protection against existing coronaviruses and estimate the extent to which this would influence transmission dynamics of a novel virus.