Studies show vaccine evasion by Omicron

Dec. 10, 2021

In quickly moving scientific developments, three separate labs that tested the Omicron (B.1.1.529) COVID-19 variant against vaccines reported significant immune escape based on reduced antibody titers, according to a news report from the Center for Infectious Disease Research and Policy at the University of Minnesota.

For early clues about impact on vaccines, researchers have been testing Omicron variant viruses (live or pseudovirus) in small numbers of patients' blood samples and comparing antibody neutralization titers against either the original COVID-19 virus or the Delta (B1617.2) variant.

The first study came from a group at Africa Health Research Institute in South Africa, led by Alex Sigal, PhD, which found a 40-fold reduction in antibody neutralization, both in people who had two doses of the Pfizer-BioNTech vaccine as well as in people who had hybrid immunity from both natural infection and a dose of Pfizer vaccine.

A short time later, a team based at Sweden's Karolinska Institute found a sevenfold reduction in blood samples from random donors and a fivefold reduction in samples from those who had earlier COVID-19 infections.

Then Sandra Ciesek, MD, Virologist and Gastroenterologist with University Hospital Frankfurt, reported that her experiments showed a 37-fold reduction in neutralization against Omicron in the blood of people who had received three doses of Pfizer, when compared with Delta. She also found no measurable Omicron neutralization 6 months after two-dose regimens of Pfizer, Moderna, or a mix of Pfizer and AstraZeneca.

Pfizer and BioNTech released similar findings. They found, on average, more than a 25-fold reduction in neutralization titers against the Omicron variant compared to wild-type virus in sera from people who had only a two-dose vaccination regimen. However, they also said serum antibodies induced by the Pfizer-BioNTech COVID-19 vaccine (BNT162b2) do appear to neutralize the SARS-CoV-2 Omicron variant after three doses of the vaccine. 

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