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Vaccine trial volunteer Franklyn Howe is given an injection at St George's University hospital at in London on Oct. 7, 2020.Alastair Grant/The Associated Press

Two-dose COVID-19 vaccine regimens do not induce enough neutralizing antibodies against the Omicron coronavirus variant, British scientists found, indicating that increased infections in those previously infected or vaccinated may be likely.

Researchers from the University of Oxford published results on Monday from a study yet to be peer-reviewed, where they analyzed blood samples from participants who were given doses from AstraZeneca-Oxford or Pfizer-BioNTech in a large study looking into mixing of vaccines.

The results come a day after British Prime Minister Boris Johnson warned that two shots will not be enough to contain Omicron, following findings from the U.K. health agency last week that boosters significantly restore protection against the variant.

The Oxford study said that there was no evidence yet that the lower level of infection-fighting antibodies against Omicron could lead to higher risk of severe disease, hospitalization or death in those who have got two doses of approved vaccines.

“These data are important but are only one part of the picture. They only look at neutralizing antibodies after the second dose, but do not tell us about cellular immunity, and this will also be tested,” said Matthew Snape, Oxford professor and co-author of the paper.

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