Why you get breakthrough COVID infection after a booster shot

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Scientists from Johns Hopkins Medicine found why after two vaccination doses and a booster shot, people still got sick from the Omicron strain of the virus that causes COVID-19.

The findings suggest that while fully vaccinated and boosted people produce a high level of antibodies that work against the original strain of SARS-CoV-2, the same tiny defenders don’t do as well in preventing the Omicron strain from attacking healthy cells.

The research is published in the Journal of Clinical Investigation Insight and was conducted by Joel Blankson et al.

In the study, the team analyzed immune responses in 18 healthy and fully vaccinated people.

These people experienced breakthrough infections within 14 to 92 days after receiving a booster COVID-19 vaccine.

Fourteen participants received a booster of the Pfizer-BioNTech messenger RNA (mRNA) vaccine.

one was boosted with the Moderna mRNA vaccine and the remaining three had an mRNA booster following their initial dose of the Johnson & Johnson viral vector vaccine.

The immune responses of those participants with breakthrough infections were compared with those who received similar COVID-19 vaccinations and boosters and had no prior infection with SARS-CoV-2.

They found that blood samples from study participants with breakthrough COVID-19—most likely the result of Omicron infection—had antibodies that strongly stopped binding by the original strain virus as expected but didn’t carry out that function as well when responding to the Omicron strain.

The levels of antibodies that inhibited spike protein binding to ACE2—high for the original strain virus but reduced for Omicron—were similar for both the participants with breakthrough infections and those in the control group.

The specific reduction in ACE2-inhibiting antibodies responding to Omicron differs from what was seen in previously studied breakthrough infections with the alpha variant.

In those cases, infected individuals were found to have lower overall antibody levels than the original virus strain.

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