Delta breakthrough infection generates broad neutralizing antibody response in double vaccinated individuals

In the new study, researchers collected sera from individuals attending St. Thomas' Hospital in London who tested positive for COVID-19 and had received 2 doses of either the Pfizer or AstraZeneca vaccines. They measured how much antibody the person produced and whether the antibodies were able to prevent infection of cells by different SARS-CoV-2 variants of concern.

The researchers 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.

"Overall, a breakthrough infection effectively boosts the vaccine response, which could provide broad protection against current variants of concern," said co-author Katie Doores, Ph.D., Reader in the Department of Infectious Diseases, King's College London, in the United Kingdom. "Recent studies show a third vaccine dose dramatically increases the neutralizing antibody response, particularly against omicron. Our data suggests a delta breakthrough infection can also act as an effective booster. This study provides insights into population immunity in double COVID-19 vaccinated individuals where SARS-CoV-2 transmission levels remain high."

Dr. Doores said they are now studying the immune response in more detail by isolating monoclonal antibodies from individuals experiencing breakthrough infections.