Two new studies said that people who have had both a full vaccine and a previous exposure to the virus have the best protection against it.
The studies highlighted the importance of getting jabbed for those who have natural immunity after recovering from the disease after two years of a Pandemic.
Brazil has the second-largest COVID death toll in the world, and one of the two studies analyzed the health data of more than 200,000 people in 2020.
It found that for people who have already had Pfizer and AstraZeneca's vaccines, they offered 90 percent effectiveness against hospitalization and death.
The four vaccines have proven to provide extra protection for those with a previous COVID-19 infection, according to the study author.
Pramod Kumar Garg of India's Translational Health Science and Technology Institute said in a comment piece that hybrid immunity due to exposure to natural infection and vaccination is likely to be the norm globally.
The study found that people who recovered from COVID retained a high level of protection against re-infection for up to 20 months.
People with two-vaccine-dose hybrid immunity had a 66 percent lower risk of re-infection.
Paul Hunter, a professor in medicine at the University of East Anglia who was not involved in the study, told Agence France-Presse that the 20 months of good protection from natural immunity was far better than expected.
He warned that both studies were completed before the Omicron variant became dominant across the world, and that it had dropped the protective value of a prior infection.
A study published on the medRxiv pre-publication website gave an insight into the protection offered by hybrid immunity.
Immunity https://t.co/ClKLHywmTT pic.twitter.com/o2V2QTz3Op
— Randall Munroe (@xkcd) December 20, 2021
It found that three vaccine doses had a 52 percent effectiveness against the symptoms of the BA.2 Omicron subvariant, but when the patient had been previously bitten, the number jumped to 77 percent.
The strongest protection against both the BA.1 and BA.2 subvariants was found in the study, which has not been peer reviewed.
Agence France-Presse
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