Scientists from King’s College London found a delta breakthrough infection generates a potent and broad neutralizing antibody response in double vaccinated people.
In the study, they collected sera from individuals who tested positive for COVID-19 and had received 2 doses of either the Pfizer or AstraZeneca vaccines.
The team measured how many antibodies the person produced and whether the antibodies were able to prevent infection of cells by different SARS-CoV-2 variants of concern.
They found that in vaccinated individuals, there was a rapid and robust IgG recall response following breakthrough infection.
This antibody response had broad neutralizing activity against current variants of concern, including omicron.
The neutralization potency was 4.5-fold reduced against omicron compared to delta, whereas it was 28.9-fold reduced for people who were unvaccinated.
The finding suggests that a breakthrough infection effectively boosts the vaccine response, which could provide broad protection against current variants of concern.
The research is published in mBio and was conducted by Katie Doores et al.
Recently, scientists from Kaiser Permanente found that three doses of the Moderna COVID-19 vaccine were highly effective against hospitalization caused by the Omicron or Delta variant.
They tested 26,683 patients who tested positive for COVID-19, 16% of whom had Delta infections and 84% of whom had Omicron infections, and more than 67,000 individuals who tested negative as a comparison group.
Researchers found two doses of the Moderna COVID-19 vaccine were 44% effective against Omicron infection within 3 months after vaccination, and effectiveness quickly declined thereafter.
Three doses of the Moderna COVID-19 vaccine within 2 months of vaccination were 94% effective against Delta infection and 72% effective against Omicron infection.
For people who had compromised immune systems, 3-dose effectiveness against Omicron infection was lower at 29%.
The 3-dose effectiveness against hospitalization with Delta or with Omicron was above 99%.
The results suggest that third doses may be needed sooner than 6 months after the second dose of the Moderna COVID-19 vaccine to protect against Omicron infection.
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