SARS-CoV-2 reinfections increased substantially after Omicron variants emerged. Large-scale
community-based comparisons across multiple Omicron waves of reinfection
characteristics, risk factors, and protection afforded by previous infection and vaccination,
are limited. Here we studied ~45,000 reinfections from the UK’s national COVID-19 Infection
Survey and quantified the risk of reinfection in multiple waves, including those driven by
BA.1, BA.2, BA.4/5, and BQ.1/CH.1.1/XBB.1.5 variants. Reinfections were associated with
lower viral load and lower percentages self-reporting symptoms compared with first
infections. Across multiple Omicron waves, estimated protection against reinfection was
significantly higher in those previously infected with more recent than earlier variants, even
at the same time from previous infection. Estimated protection against Omicron reinfections
decreased over time from the most recent infection if this was the previous or penultimate
variant (generally within the preceding year). Those 14-180 days after receiving their most
recent vaccination had a lower risk of reinfection than those >180 days from their most
recent vaccination. Reinfection risk was independently higher in those aged 30-45 years,
and with either low or high viral load in their most recent previous infection. Overall, the
risk of Omicron reinfection is high, but with lower severity than first infections; both viral
evolution and waning immunity are independently associated with reinfection.
