The preliminary study in South Africa, based on data from those who have been double jabbed who had a prior infection, found a “very large drop” in neutralisation of Omicron compared to an earlier variant.
However, W.H.O’s Dr Mike Ryan said he expected that vaccines would still remain effective against the variant.
“We have highly effective vaccines that have proved effective against all the variants so far, in terms of severe disease and hospitalisation, and there’s no reason to expect that it wouldn’t be so” for Omicron, he told AFP news agency.
He also said indications were that Omicron did not make people sicker than the Delta variant, which is currently dominant in the UK. “If anything, the direction is towards less severity,” he said.
The South African study, which is not yet peer reviewed, tested blood from 12 people given two doses of Pfizer, and found that the vaccine appears less effective against Omicron than earlier variants.
However, researcher Alex Sigal said Omicron’s ability to escape vaccine antibodies is “incomplete” and that the results were “better than I expected of Omicron”.
There are a few results:
1. Omicron still uses ACE2
2. There is a very large drop in neutralization of Omicron by BNT162b2 immunity relative to ancestral virus
3. Omicron escape from BNT162b2 neutralization is incomplete. Previous infection + vaccination still neutralizes
— Alex Sigal (@sigallab) December 7, 2021
Professor Sigal’s study also suggested that a combination of vaccinations and prior infection could still neutralise against Omicron - suggesting boosters could help stave off infection.
More research on the effectiveness of Pfizer against Omicron is expected to be released within days.
Significant studies on how well the Moderna, Johnson & Johnson and other jabs hold up against Omicron are yet to be published.
The early findings come as the Government said early signs were that Omicron was more transmissible than Delta.
However, the prime minister’s spokesperson said on Tuesday that the impact of the variant would depend on whether it caused severe illness.