Vaccination after COVID improves immunity

Although people who recover from COVID-19 usually gain some immune defenses against reinfection, they get additional protection from vaccines, especially against severe disease, according to two studies published on Thursday in The Lancet Infectious Diseases.

One study of 22,566 people in Brazil who had recovered from COVID found that all four vaccines in use there – from Sinovac Biotech , AstraZeneca, Johnson & Johnson, and Pfizer/BioNTech – provided significant additional protection. Effectiveness against infection starting 14 days after vaccination completion ranged from 39.4% for Sinovac’s CoronaVac to 64.8% for the Pfizer/BioNTech shots. Effectiveness against hospitalization or death ranged from 81.3% for CoronaVac to 89.7% for Pfizer/BioNTech’s vaccine.

The second study, using data from more than 5 million people in Sweden, found that “hybrid immunity” from a combination of previous infection and receipt of either one or two doses of a vaccine provided additional protection for at least nine months. “One-dose hybrid immunity was associated with an additional 94% lower risk of COVID-19 hospitalization, and two-dose hybrid immunity with an additional 90% lower risk of COVID-19 hospitalization,” compared to natural immunity alone, the researchers said. Neither study included patients infected or reinfected with the Omicron variant.

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