June 4, 2021 -- The Pfizer COVID-19 vaccine produces lower levels of antibodies against the Delta variant, known as B.1.617.2 and discovered in India, according to a new study published Thursday in The Lancet.

The antibody levels also appear to be lower in older people and decline over time, which could mean that some vaccinated people will need a booster shot this fall.

“This virus will likely be around for some time to come, so we need to remain agile and vigilant,” Emma Wall, PhD, the lead study author and an infectious diseases specialist at the Francis Crick Institute in London, said in a statement.

“The most important thing is to ensure that vaccine protection remains high enough to keep as many people out of hospital as possible,” she said. “And our results suggest that the best way to do this is to quickly deliver second doses and provide boosters to those whose immunity may not be high enough against these new variants.”

The research team analyzed antibodies in the blood of 250 healthy people, ages 33-52, up to 3 months after receiving their first dose of the Pfizer COVID-19 vaccine. The team looked for “neutralizing antibodies,” or the ability of antibodies to block the virus from entering cells.

The researchers tested five variants: the original strain discovered in China, the dominant strain in Europe during the first wave in April 2020, the B.1.1.7 variant discovered in the U.K., the B.1.351 variant first seen in South Africa, and the newest variant of concern, which is the B.1.617.2 variant discovered in India.

The team compared the concentrations of the neutralizing antibodies among the variants. They found that people who had been fully vaccinated with two Pfizer doses had antibodies that were 6 times lower against the B.1.617.2 variant, 5 times lower against the B.1.351 variant, and 2.6 times lower against the B.1.1.7 variant when compared to the original strain.

The antibody response was even lower in people who had received only one dose. After a single Pfizer dose, 79% of people had neutralizing antibodies against the original strain, which fell to 50% for the B.1.1.7 variant, 32% for the B.1.617.2 variant, and 25% for the B.1.351 variant.

The study group plans to continue its research on neutralizing antibodies and the variants, including in people who have been vaccinated with the AstraZeneca vaccine.

“New variants occur naturally, and those that have an advantage will spread. We now have the ability to quickly adapt our vaccination strategies to maximize protection where we know people are most vulnerable,” David Bauer, PhD, the senior study author and group leader of the Francis Crick Institute’s RNA Virus Replication Laboratory, said in the statement.

“Keeping track of the evolutionary changes is essential for us to retain control over the pandemic and return to normality,” he said. “This work … can help us to navigate changes in this new phase of the pandemic.”

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The Lancet: “Neutralizing antibody activity against SARS-CoV-2 VOCs B.1.617.2 and B.1.351 by BNT162b2 vaccination.”

The Francis Crick Institute: “Pfizer-BioNTech vaccine recipients have lower antibody levels targeting the Delta variant first discovered in India.”

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