Scientists discovered that two doses of the Oxford-AstraZeneca or Pfizer-BioNTech Covid-19 vaccines are significantly less effective at protecting against omicron than prior coronavirus versions.
The researchers were hopeful, however, that a booster dose would raise immunity to the new, highly transmissible strain.
Researchers from the University of Oxford analyzed blood samples of participants 28 days after receiving their second dose of either vaccine in a new study released on Monday.
When omicron was added to those samples, scientists noticed a “significant drop” in neutralizing antibodies that combat Covid when compared to immune responses to previous variations. Some vaccine recipients failed to neutralize the virus at all, according to the study.
“This will likely lead to increased breakthrough infections in previously infected or double vaccinated individuals, which could drive a further wave of infection, although there is currently no evidence of increased potential to cause severe disease, hospitalization or death,” the study’s authors said.
The paper was released on the MedRxiv platform as a pre-print that has yet to be peer reviewed.
The findings should “drive home the message that those who are offered booster immunization should accept it,” said Gavin Screaton, dean of Oxford University’s Medical Sciences Division and principal author of the article, in a press statement on Monday.
“Whilst there is no evidence for increased risk of severe disease, or death, from the virus amongst vaccinated populations, we must remain cautious, as greater case numbers will still place a considerable burden on healthcare systems,” he warned.
“Vaccination induces many arms of our immune system, including neutralizing antibodies and T-cells,” added co-author Teresa Lambe, a professor of vaccinology at the University of Oxford.
“Real-world effectiveness data has shown us that vaccines continue to protect against severe disease with previous variants of concern. The best way to protect us going forward in this pandemic is by getting vaccines in arms.”
According to a report released on Friday by the UK’s Health Security Agency, two doses of a Covid vaccine were much less successful than delta at avoiding symptomatic disease from infection with the omicron form. Vaccines, however, were estimated to be 70 to 75 percent effective at preventing symptomatic infections after a booster dose, according to the paper.
“With previous variants, vaccine effectiveness against severe disease, including hospitalization and death, has been higher than effectiveness against mild disease,” the UKHSA said. “It will be a few weeks before effectiveness against severe disease with Omicron can be estimated, however based on this experience, this is likely to be substantially higher than the estimates against symptomatic disease.”
Boris Johnson, the Prime Minister of the United Kingdom, warned that the country is facing a “tidal wave” of Omicron infections in a televised statement on Sunday, and announced that the country would be speeding up its booster program to offer all adults a third dose of the vaccine by the end of the year. The government had hoped to extend its booster scheme to everyone over the age of 18 by the end of January.
In light of the spread of omicron, the chief medical officers of England, Scotland, Wales, and Northern Ireland elevated the United Kingdom’s coronavirus threat level to four, the second highest level.
A three-dose course of the Pfizer-BioNTech vaccine gave considerable protection against the omicron form, according to an Israeli study published on Saturday. Israel’s booster program began in July.
The Israeli discoveries come after South African researchers discovered that omicron could partially evade protection from two shots of the Pfizer-BioNTech vaccine.
The omicron strain, which is thought to be more contagious than its ancestor delta, was discovered in South Africa in November and has since spread to at least 38 nations and 25 US states.
