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Reinfections are probable, not good news actually How likely somebody who has already had Covid to catch Omicron? (catching it twice or more) Increased risk of SARS-CoV-2 reinfection associated with emergence of the Omicron variant in South Africa What is already known on this topic https://www.medrxiv.org/content/10.1101/2021.11.11.21266068v2.full.pdf Prior infection with SARS-CoV-2 is estimated to provide 84% reduction in infection risk What this study adds We find no evidence of increased reinfection risk associated with circulation of Beta or Delta variants, compared to the ancestral strain in routine epidemiological data from South Africa. In contrast, we find clear, population-level evidence to suggest substantial immune evasion by the Omicron variant. Omicron selection advantage is at least partially driven by an increased ability to infect previously infected individuals. Omicron variant increases reinfection risk - Yes Omicron variant of SARS-CoV-2 demonstrates substantial population-level evidence for evasion of immunity from prior infection. Retrospective analysis of routine epidemiological surveillance data 4th March 2020 to 27th November 2021 South Africa’s National Notifiable Medical Conditions Surveillance System N = 2,796,982 Laboratory-confirmed SARS-CoV-2 Results 35,670 suspected reinfections were identified among 2,796,982 individuals with laboratory-confirmed SARS-CoV-2, who had a positive test result at least 90 days prior to 27th November 2021 35,670 individuals with at least two infections 332 individuals with third infections 1 individual with four infection The relative hazard ratio for wave 2 versus wave 1 was 0.75 The relative hazard ratio for wave 3 versus wave 1 was 0.71 Relative hazard ratio for the period from 01 November 2021 to 27 November 2021 The relative hazard ratio for wave 4 versus wave 1 was 2.39 In the time of beta and delta Increases in primary infections No corresponding increase in reinfection hazard In the time of omicron Omicron variant, decrease in the hazard for primary infection Increase in reinfection hazard coefficient Conclusion Population-level evidence suggests that the Omicron variant is associated with substantial ability to evade immunity from prior infection. In contrast, there is no population-wide epidemiological evidence of immune escape associated with the Beta or Delta variants. This finding has important implications for public health planning, particularly in countries like South Africa with high rates of immunity from prior infection. Urgent questions remain regarding whether Omicron is also able to evade vaccine-induced immunity, and the potential implications on protection against severe disease and death. Prof Paul Hunter The implications of this paper are that Omicron will be able to overcome natural and probably vaccine-induced immunity to a significant degree. But, the degree is still unclear - though it is doubtful that this will represent complete escape. Prof Francois Balloux, University College London The higher estimated re-infection ability of the Omicron variant to cause re-infection is not overly surprising and could be largely anticipated based on the large number of mutations in the spike protein carried by the omicron variant, which increase the Omicron variant's ability to bypass host immunity

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