Vaccination against Covid-19 provides stronger immunity protection against previous infection with the coronavirus, according to A study From the Centers for Disease Control and Prevention published Friday.
The study looked at more than 7,000 people who were hospitalized with Covid-like illnesses, and found that those who had not been vaccinated – but had a previous case of the disease – were five times more likely to contract Covid than people who were fully vaccinated. He had never had Covid before.
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Previous infection provides a certain degree of immunity and protection against reinfection, but the results suggest that the protection conferred by vaccination is stronger.
“We now have additional evidence that reaffirms the importance of Covid-19 vaccines, even if you have a previous infection,” CDC Director Dr. Rochelle Walinsky said in a statement.
Dipta Bhattacharya, a professor of immunology at the University of Arizona, cautioned that it can be very difficult to compare vaccine-induced immunity to infection-induced immunity.
“What I would say is that these are probably not the right terms for discussion,” he said. “The reason I prefer vaccine-induced immunity is because infection can make you really sick, not because it doesn’t leave you immune.”
In the study, researchers looked at people hospitalized with COVID symptoms at 187 hospitals across nine states from January to September — a period that included both alpha and delta variables. Patients were included if they had a previous case of Covid in the past three to six months, or had been fully vaccinated with either the Pfizer-BioNTech vaccine or the Moderna vaccine in the past three to six months. The researchers said Johnson & Johnson vaccine recipients were not included due to a lack of sufficient data.
A total of 6,328 fully vaccinated people in the study were hospitalized with Covid-like illnesses, but of them only 324, or 5.1 percent, tested positive for the virus. In the second group — who was not immunized but had previously been infected — there were a total of 1,020 people in hospital, 89 of whom, or 8.7 percent, had tested positive for the virus.
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The Pfizer and Moderna vaccines provided higher protection against previous infections. Protection from the Moderna vaccine was stronger than that from the Pfizer vaccine, a finding noted in Previous CDC Report. The protective effects of vaccines were also higher in adults 65 years of age or older than in people 18-64 years old.
Because the study only included people who had been vaccinated or previously infected within the previous six months, the researchers cautioned that the protective effects may wane over time.
Previous research has shown that so-called hybrid immunity, or natural immunity from a previous infection in addition to immunity induced by a vaccine, leads to particularly strong protection – another reason why people who have previously been infected should be vaccinated.
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Akshay Sial, MD Contributed.
