In a study from the University of Lisbon and elsewhere, scientists found vaccines and past COVID infection offer long-lasting protection from omicron BA.5.
A previous study from the team showed that infection by the first omicron subvariants of SARS-CoV-2, circulating in January and February 2022, provided considerable protection against the omicron BA.5.
However, the stability of the protection from the so-called hybrid immunity, the immunity conferred by the combination of vaccination and infection, was not yet known.
In the study, the team used the national COVID-19 case registry until September 2022, which is especially comprehensive due to the legal requirement to register all cases of SARS-CoV-2 infection at the time to gain access to sick leave during mandatory isolation days.
They used the national COVID-19 case registry to obtain information of all cases of SARS-CoV-2 infections in the population over 12 years old residing in Portugal.
These data from the Portuguese population allow the team to conclude about hybrid immunity because vaccination had already covered 98% of this population by the end of 2021.
The virus variant of each infection was determined considering the date of infection and the dominant variant at that time.
The team calculated the relative risk of reinfection over time in people vaccinated with previous infections by the first omicron subvariants of SARS-CoV-2.
They found that protection remains high 8 months after contact with the virus.
The protection afforded by hybrid immunity is initially about 90%, reducing after 5 months to about 70%, and showing a tendency to stabilize at a value of around 65% after 8 months, compared to the protection in vaccinated persons that were never infected by the virus.
These results show that hybrid immunity conferred by infection with previous subvariants of SARS-CoV-2 in vaccinated people is quite stable.
This study shows that infection by previous subvariants of the SARS-CoV-2 virus, which causes COVID-19, has the ability to confer additional protection compared to the protection conferred by vaccination alone, and that this protection is stable.
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The study was conducted by Luís Graça et al and published in the journal Lancet Infectious Diseases.
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