Two vaccine doses after COVID-19 strongly boost antibody levels

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In a new study from Karolinska Institutet, researchers found antibodies in the airways quickly wane after SARS-CoV-2 infection, but vaccination results in a strong increase in antibody levels, especially after two doses.

The results suggest that having a second dose of the vaccine also after recovering from COVID-19 may be important for preventing re-infection and transmission.

In their study, the researchers examined how the levels and durability of the antibodies to SARS-CoV-2 differed between individuals who had mild to severe COVID-19.

147 patients were recruited in March to May 2020 and monitored for up to eight months after infection. In 20 of the patients, they also studied antibody levels after vaccination (with the AstraZeneca, Pfizer-BioNTech or Moderna vaccine) and compared the results with a control group that had not previously had COVID-19.

The team found that individuals who underwent more severe COVID-19 disease had higher antibody levels upon recovery compared to individuals with mild disease.

The antibodies in the blood remained at measurable levels for at least eight months, while those in the airways (e.g. the nose) were short-lived and disappeared already after three months.

The team also found that the antibodies quickly returned after vaccination in those who previously had COVID-19, not only in the blood but also in the airways.

The antibody levels in the airways after two doses of vaccine were often even higher than they were during the course of the disease. People who had not had COVID-19 before vaccination had much lower or undetectable levels.

In the COVID-19 patients, the second vaccine dose did not have such a strong effect on the antibody levels in the blood.

The results demonstrate that completing the vaccination with a second dose may therefore be important for achieving optimal immune responses and reducing the spread of infection between individuals.

The study is published in the journal JCI Insight. One author of the study is Anna Smed-Sörensen.

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