The Omicron variant can partially evade the protection from two doses of Pfizer's COVID-19 vaccine, the research head of a laboratory in South Africa says.
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Alex Sigal, a professor at the Africa Health Research Institute, said on Twitter there was "a very large drop" in neutralisation of the Omicron variant relative to an earlier strain of COVID-19.
But the study showed blood from people who had received two doses of the vaccine and had a prior infection were mostly able to neutralise the variant, suggesting booster doses of the vaccine could help to fend off infection.
The lab tested blood from 12 people who had been vaccinated with two doses of the Pfizer-BioNTech vaccine, according to a manuscript posted on its official website. The preliminary data in the manuscript has not yet been peer reviewed.
Blood from five out of six people who had been vaccinated as well as previously infected with COVID-19 still neutralised the Omicron variant, the manuscript said.
"These results are better than I expected. The more antibodies you've got, the more chance you'll be protected from Omicron," Sigal said on Twitter.
He said the lab had not tested the variant against blood from people who had received a booster dose, because they are not yet available in South Africa.
According to the manuscript, the lab observed a 41-fold decline in levels of neutralising antibodies against the Omicron variant.
Sigal said on Twitter that figure is likely to be adjusted after his lab does more experiments.
While neutralising antibodies are an indicator of the body's immune response, scientists believe other kinds of cells such as B-cells and T-cells also are stimulated by the vaccines and help protect against the effects of the coronavirus.
Preliminary data does not indicate the vaccine is less able to prevent severe illness or death. While lab tests are under way, BioNTech CEO Ugur Sahin said last week "we think it's likely that people will have substantial protection against severe disease caused by Omicron".
The Omicron variant, first detected in southern Africa last month, has sounded alarms globally of another surge in infections, with more than two dozen countries reporting cases.
The World Health Organization classified Omicron on November 26 as a "variant of concern", but said there was no evidence to support the need for new vaccines.
There is not significant data yet on how vaccines from Moderna, Johnson & Johnson and other drugmakers hold up against the new variant. All manufacturers, including Pfizer, are expected to release their own data within weeks.
Top US infectious diseases expert Dr Anthony Fauci said on Tuesday preliminary evidence indicates Omicron probably has a higher degree of transmissibility but is less severe.
Umer Raffat, an analyst for Evercore ISI, cautioned against reading too much into a single study, noting there has been significant variability in measuring declines in antibody levels in previous lab studies.
"Let's wait for additional studies to draw a mosaic," he said.
Australian Associated Press
