Two new studies published last Friday indicate that individuals with "hybrid immunity," characterized by full vaccination and previous infection with COVID-19, possess the strongest protection against the virus, according to the scientific website "Science Alert," citing Agence France-Presse.
After two years of a pandemic that affected nearly 500 million people and vaccinated billions, the studies emphasize the importance of exposure to infections for those with natural immunity after recovering from the disease.
One of the studies published in the medical journal "The Lancet Infectious Diseases" analyzed health data for over 200,000 individuals in heavily affected Brazil during 2020 and 2021, which has the second-highest number of COVID-19 deaths globally. It found that for individuals who had previously contracted COVID-19, the Pfizer and AstraZeneca vaccines provided 90% effectiveness against hospitalization and death, while the Chinese vaccine yielded 81%, and one dose of Johnson & Johnson resulted in 58%.
In this context, study author Julio Croda from the Federal University of Mato Grosso do Sul stated, "All four of these vaccines have proven to provide significant additional protection for those who had a previous COVID-19 infection."
Meanwhile, a study conducted using the Swedish national registry up to October 2021 found that individuals who recovered from COVID-19 maintained a high level of protection against reinfection for up to 20 months. Those with hybrid immunity from two vaccine doses were 66% less likely to be at risk of reinfection compared to individuals with only natural immunity.
To clarify further, Paul Hunter, a professor of medicine at the University of East Anglia who did not participate in the study, told Agence France-Presse that 20 months of "very good protection" from natural immunity was "much better than we would have expected for the original two doses." However, he cautioned that both studies were completed before the Omicron variant became dominant worldwide, and that the "protective value of previous infection has significantly decreased."
A study in Qatar published on the preprint server medRxiv last week provided insight into the protection offered by hybrid immunity against Omicron. It found that three doses of the vaccine had 52% effectiveness against symptomatic infections of Omicron BA.2; however, this figure jumped to 77% if the patient had been previously infected. The unpublished study noted that "hybrid immunity resulting from previous infection and recent booster vaccination provides the strongest protection" against both subvariants BA.1 and BA.2.
