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Hybrid Immunity Provides Longer Protection Than Past COVID Infection

Hybrid Immunity Provides Longer Protection Than Past COVID Infection

A nurse displays a vial of Covishield. Photo: Reuters/Francis Mascarenhas

  • Three studies from Brazil, Sweden and the UK all found that natural immunity that is boosted by vaccines provides greater protection against COVID-19 reinfection.
  • One of the studies suggests that since countries should pivot from ‘vaccine passports’ to ‘immunity passports’ and remove restrictions for people who have had COVID-19.
  • These studies were conducted before the omicron variant became the global strain and may have limited relevance today.

New Delhi: Three recent studies have made the case that even people who have had COVID-19 benefit greatly from getting vaccinated and ‘hybrid immunity’ – a combination of natural immunity and vaccine acquired immunity – confers longer protection from SARS-CoV-2.

The first study, conducted in Brazil, was prompted by claims made by the country’s President Jair Bolsonaro that he would not take the vaccine because he had already been infected by the coronavirus. In India too, similar claims have been made by some individuals. The researchers drew from Brazilian vaccination and infection databases to test such assertions.

Between February 2020 and November 2021, they tracked reinfections among people who did not take the vaccine and those who received one dose and two doses. According to Nature News, the study found that people who previously had COVID-19 and then received one dose of the vaccine – made by Pfizer, AstraZeneca, SinoVac or Johnson & Johnson – had a 45% lower risk of reinfection compared to those who were unvaccinated. Those who received both doses had 65% lower risk of expected infections.

“The big message is this: you need to have a full vaccination scheme for COVID-19,” Julio Croda, a co-author and an infectious-disease doctor and epidemiologist at the Oswaldo Cruz Foundation in Rio de Janeiro, told Nature News.

“All four vaccines conferred additional protection against symptomatic infections and severe outcomes among individuals with previous SARS-CoV-2 infection. The provision of a full vaccine series to individuals after recovery from COVID-19 might reduce morbidity and mortality,” the authors wrote in the study.

Immunity passports vs vaccine passports

The second study, conducted in Sweden, also came to similar conclusions. Using records collected by the country’s Public Health Agency between March 2020 and October 2021, the researchers found that a COVID-19 infection reduces the risk of contracting it again by 95% when compared to people with no immunity. Crucially, the study says protection grew over the three months following infection and lasted until at least 20 months after infection. Additionally, receiving one dose of vaccine reduced the risk of infection by an additional 58%, while the second dose “stabilised the additional protection over the six months following vaccination”, according to Nature News.

However, the authors said while having hybrid immunity was associated with a lower risk of COVID-19 hospitalisation than natural immunity, “the differences in absolute numbers, especially in hospitalisations, were small”.

“The risk of SARS-CoV-2 reinfection and COVID-19 hospitalisation in individuals who have survived and recovered from a previous infection remained low for up to 20 months. Vaccination seemed to further decrease the risk of both outcomes for up to 9 months, although the differences in absolute numbers, especially in hospitalisations, were small,” they wrote.

They recommended that countries that consider only vaccine-acquired immunity to allow people access to public spaces may expand these “passports” to those who previously had COVID-19. Peter Nordström, an epidemiologist at Umeå University in Sweden who was a co-author of the study, told Nature News, “Perhaps we should have immunity passports instead of vaccination passports. So you are considered immune – and less likely to transmit the disease – if you have been fully vaccinated, or you have had a documented previous infection.”

The third study, which followed health workers in the UK between December 7, 2020, and September 21, 2021, found that people who received two doses of the COVID-19 vaccines were associated with “high short-term protection against SARS-CoV-2 infection”, which waned considerably after 6 months. “Infection-acquired immunity boosted with vaccination remained high more than 1 year after infection,” they wrote.

“Protection declined over time after vaccination, and also after infection, but remained persistently high in those with hybrid immunity,” one of the authors told Nature News.

Because these studies were conducted before the omicron variant became the dominant global strain, other scientists told Nature News that the findings may have limited relevance today. Both natural immunity and vaccine-acquired immunity have been less effective against this variant.

Dan Kelly, an infectious-disease epidemiologist based in San Francisco, US, said omicron is “so different from the strains analysed in the studies” that the findings “might not apply to people who were infected with omicron after being vaccinated”.

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