The Oxford-AstraZeneca or Pfizer-BioNTech Covid-19 vaccines are less effective at warding off omicron than previous versions of the coronaviruses, according to scientists.
The researchers were optimistic that a booster shot would improve immunity.
Researchers from the University of Oxford tested blood samples of people 28 days after their second vaccine dose.
Scientists reported that when omicron was introduced to those samples, the neutralizing antibodies that fight off Covid fell.
Some vaccine recipients failed to destroy the virus according to the research paper.
There is currently no evidence of increased potential to cause severe disease, hospitalization or death, but this will likely lead to increased breakthrough infections in previously infectious individuals, which could drive a further wave of infections.
The pre-print study was published on the MedRxiv server.
The lead author of the paper said in a press release on Monday that the findings should "press home the message that those who are offered booster vaccine should take it."
There is no evidence for increased risk of death or severe disease from the vaccine, but we must remain cautious as case numbers will still place a considerable burden on healthcare systems.
Teresa Lambe, a professor of vaccinology at the University of Oxford, said that vaccinations cause many arms of the immune system.
Real-world effectiveness data has shown that vaccines are still effective against severe disease. Getting vaccines in arms is the best way to protect ourselves.
The report by the Health Security Agency in the U.K. said that two doses of the Covid vaccine were not as effective as one dose of the Delta vaccine. The report stated that the vaccines were 70 to 75% effective at preventing infections.
The UKHSA said that vaccine effectiveness against severe disease, including hospitalization and death, has been higher than against mild disease. It will be a few weeks before the effectiveness against Omicron can be estimated, however based on this experience, this is likely to be substantially higher than the estimates against the disease.
In a televised statement on Sunday, the Prime Minister of the U.K. Boris Johnson warned that Britain faces a "tidal wave" of Omicron infections and that the country would be speeding up its booster program to offer all adults a third dose of a vaccine by the end of the The booster scheme was supposed to be extended to all over-18s by the end of January.
The chief medical officers of England, Scotland, Wales and Northern Ireland raised the U.K.'s coronaviruses threat level to four, the second highest level, due to the spread of omicron.
A three-dose course of the Pfizer-BioNTech vaccine provided significant protection against the omicron variant, according to an Israeli study. Israel began its booster program in July.
Researchers in South Africa found that omicron could partially evade the immunity from two shots of the Pfizer-BioNTech vaccine.
The omicron variant was first identified in South Africa in November and has since spread to at least 38 countries around the world and 25 U.S. states.
