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
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
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
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