December 15, 2021: Scientists have found that two doses of the Oxford-AstraZeneca or Pfizer-BioNTech Covid-19 vaccines are substantially less effective at warding off Omicron than previous variants of the coronavirus.

However, the researchers were optimistic that a booster dose would improve immunity against the new transmissible variant.

On Monday, a new study announced, researchers from the University of Oxford tested blood samples of people 28 days after their second dose of either vaccine.

When Omicron was showcasing to those samples, scientists reported: “a substantial fall” in the neutralizing antibodies that fight off Covid comparing to the immune responses seen against the variants.

On Monday, Gavin Screaton, head of Oxford University’s Medical Sciences Division and lead author of the paper, said that the findings should “press home the message that those who are offered booster vaccination should take it.”

“While there is no evidence for increased risk of severe disease, or death, from the virus amongst vaccinated populations, remaining cautious, as greater case numbers will still place a considerable burden on healthcare systems,” he warned.

“Vaccination inducing many arms of our immune system, which include 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 last variants of concern. The only way to protect us going forward in this pandemic is by getting vaccines in arms.”

On Friday, a report published by the U.K.’s Health Security Agency estimated that two doses of a Covid vaccine were huge less effective at preventing symptomatic disease through infection from the omicron variant than the delta. However, the report noted that vaccines were thought to be 70 to 75% effective at preventing symptomatic infections after a booster dose.

“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 to be slightly higher than the estimates against symptomatic disease,” the UKHSA added.

In a televised statement on Sunday, U.K. Prime Minister Boris Johnson warned Britain faces a “tidal wave” of Omicron infections and announced that the country would be speeding up its booster program to offer all adults the third dose of a vaccine by the year-end. The government had previously aimed to extend its booster scheme to all over-18s by the end of January.

The findings from Israel came after researchers in South Africa found Omicron could evade the immunity from two doses of the Pfizer-BioNTech vaccine.

The omicron variant, thought to be infectious than its predecessor delta, was first identified in South Africa and has since spread to nearly 38 countries worldwide and 25 U.S. states.