Pfizer says Omicron may require three vaccine doses

By Melissa Coade

Friday December 10, 2021

A third dose of an Omicron vaccine will likely be needed. (angellodeco/Adobe)

New data sets released in the last two days have indicated a drop in immunity against the Omicron variant, based on analyses of blood from people who have recovered from COVID-19 or been vaccinated against the disease.

On Wednesday, the vaccine manufacturer released the results of preliminary lab studies showing the effect of the Pfizer-BioNTech COVID-19 vaccine on the latest virus variant. 

Two shots of the vaccine ‘significantly reduced neutralization titers’ and may still reduce protection from severe disease, Pfizer said, while three doses ‘neutralised’ the Omicron (B.1.1.529 lineage) variant.

In a statement, BioNTech CEO Uğur Şahin said a third dose of the vaccine was likely to offer a sufficient level of protection from a disease of any severity caused by the new variant. 

“Broad vaccination and booster campaigns around the world could help us to better protect people everywhere and to get through the winter season,” Şahin said. 

“We continue to work on an adapted vaccine which, we believe, will help to induce a high level of protection against Omicron-induced COVID-19 disease as well as a prolonged protection compared to the current vaccine.”

The vaccine manufacturer began working on developing an Omicron specific vaccine on November 25 in the event that an adapted vaccine will be needed to increase the level and duration of protection.

Pending regulatory approval, Pfizer-BioNTech said a new Omicron-based vaccine could be delivered in 100 days with no impact on its commitment to produce another four billion doses of the BNT162b2 vaccine next year.

Pfizer CEO Albert Bourla added that ensuring as many people as possible were fully vaccinated with an initial two-dose series and a booster was the best way to prevent further spread of the virus.

“Although two doses of the vaccine may still offer protection against severe disease caused by the Omicron strain, it’s clear from these preliminary data that protection is improved with a third dose of our vaccine,” Bourla said.

Other studies support early findings

This adds to the findings from a small study in South Africa, yet to be peer-reviewed, that has shown antibody neutralisation may be reduced by around 40-fold against Omicron compared to the original Wuhan virus.

Virologist Dr Vinod Balasubramaniam from the Jeffrey Cheah school of medicine & health sciences at Monash University Malaysia explained that the research out of South Africa used human lung cells for its tests.

[Scientists] mixed a live virus (grown in the lab) with blood samples of six people who had two doses of Pfizer. They also mixed the virus with blood samples of six people with the two-dose series and a previous infection,” Balasubramaniam said.

“In order to assess vaccine ‘effectiveness’, the scientists counted the number of neutralising antibodies that attached to Omicron. Neutralizing antibodies plays a significant role in our protection against infection, as they quickly recognise the virus and destroy it.”

Balasubramaniam went on to say that neutralizing antibodies destroyed the virus before entering cells, preventing it from replicating.

“Importantly, neutralising antibodies is not our only defence. We have other antibodies, B-cell factories, and T-cells that will also help protect against severe disease and death. It will take time and more data to determine if we need an Omicron-specific booster,” Balasubramaniam said.

“We’re going to see an increase in breakthrough cases, especially among those with only the primary series. But this study gives me great hope that our boosters will help protect against Omicron,” he added. 

Another separate early study, also to be peer-reviewed, demonstrated a significant drop in the ability of vaccine generated antibodies to neutralise the virus.

Results vary but need for boosters clear

Commenting on the release of the preliminary results, Dr Deborah Cromer from UNSW’s Kirby Institute said that while all the studies found less immunity against Omicron than against the original virus strain, the reported drops varied widely. 

Despite this, she said, it was clear at the very least that increased levels of immunity were needed to protect the community from this new COVID variant.

“The estimates we have seen to date of people’s immunity against Omicron range from half to one-fortieth of the immunity present against the original strain. 

“The work now begins to reconcile all the data together to establish a robust answer to this important question,” Cromer said.

“Booster shots are now more important than ever,” she added.

University of Sydney school of medicine Professor Sarah Palmer agreed about the importance of having boosters available for the community. She also highlighted that the preliminary results were based on a very small sample (of fewer than 40 patients) and only reflected immune response results within only one month of receiving a booster. 

“The study Pfizer has reported indicates that the original two-dose vaccination may be less effective against the Omicron variant. This underscores all the more the need to get boosters to mitigate infection from Omicron and possibly other variants,” Palmer said. 

“However, we simply do not know the long-term efficacy of the Pfizer booster against Omicron or other variants. That will have to await continued studies.”


Questions remain about Omicron variant R value and risk of ‘breakthrough’ infection

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