FRIDAY, Oct. 15, 2021 (HealthDay News) -- The Moderna and Pfizer COVID vaccines protect against a number of coronavirus variants, including highly contagious Delta, another study confirms.
The findings come as breakthrough infections in vaccinated people raise questions about the vaccines' ability to protect against emerging variants.
The shots do "induce high levels of antibodies against Delta and most variants," said study co-author Akiko Iwasaki, a professor of immunobiology at Yale University. "And two shots are better than one."
Booster shots can also help protect against infection, according to the findings. They were published Oct. 11 in the journal Nature.
For the study, the researchers collected blood samples from 40 health care workers between November 2020 and January 2021, before vaccination.
In the following weeks, more blood samples were collected after volunteers had their first and second doses of the Moderna or Pfizer-BioNTech vaccines.
The blood samples were then exposed to 16 coronavirus variants, including Delta -- currently the most common strain in the United States. Blood collected after vaccination showed enhanced immune response, but it did vary by variant and individual.
In general, immune response was robust against the Delta variant, and even stronger after the participants' second shots.
Delta-related breakthrough infections are not likely to be the result of vaccine failure, according to Iwasaki, but instead due to the variant's extreme infectiousness, which can overwhelm the immune defense.
The researchers also found that people who had COVID prior to vaccination had a stronger immune response after getting their shots than those who had never been infected.
"Recovering from an initial infection is like getting a first vaccine shot," Iwasaki said in a university news release.
A booster shot could have a similar effect, boosting levels of antibodies and T-cells that protect against infection, she suggested.
The U.S. Centers for Disease Control and Prevention has more on COVID-19 vaccines.
SOURCE: Yale University, news release, Oct. 11, 2021
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