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Pfizer Boosters Show Some Benefit Against Omicron, Initial Data Suggests


Dr. Katie Spalding

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory.

Freelance Writer

Pfizer vaccine

Omicron is able to escape vaccine antibodies – but not completely. Image credit: cortex-film/

It’s been a worrying couple of weeks, hasn’t it? Ever since Omicron turned up two weeks ago, the news has been a tumultuous onslaught of unknowns: will it be worse than normal COVID-19? Is it more infectious? How will our vaccines hold up against the new variant’s mutations?

Now, thanks to tireless work from scientists in South Africa, we have the first drips of real information about Omicron's ability to escape the Pfizer vaccine. A report, not yet peer-reviewed and based on just 12 participants, was released last night from the Africa Health Research Institute in Durban, South Africa, and here’s the takeaway: it’s bad, but not as bad as it could be.


Omicron is able to escape vaccine antibodies – but not completely.

“This was better than I expected of Omicron,” study lead Dr Alex Sigal tweeted Tuesday night when he announced the results. “It’s a tractable problem with the tools we [have] got.”

A key fear among virologists when the Omicron variant was first spotted was that its high number of mutations – a staggering 15 in the receptor-binding domain alone – may render current vaccines useless. If the virus could evolve a new infection route, not using the ACE2 receptor, then “all our efforts would be trash,” Sigal told the New York Times.

But luckily, that’s not what happened.


“The virus is using the same door into our cells … as before,” explained epidemiologist Katelyn Jetelina, who was not involved in the research. “This is very good news because it means our tools (like vaccines) are still useful. If the virus found a different door, this may not have been the case.”

But it’s not all good news.

The team introduced the Omicron virus to blood samples taken from 12 people who had received a double dose of the Pfizer mRNA vaccine. Half of the samples were taken from people who had also experienced a previous infection, and half had not – booster shots aren’t yet widely available in South Africa, but previous infection is “a good proxy,” Jetelina said.

When the researchers measured the titers – that is, the concentrations of neutralizing antibodies in the samples – of people with two doses of Pfizer, they found a huge 41-fold decline with Omicron compared to the original virus, the report reveals. That means the virus is much better at evading our body’s defenses than previous strains. As a comparison, researchers saw neutralizing titers decrease about four to six-fold for the Delta variant.

Neutralizing antibodies against the Omicron variant, compared to the original variant, in participants who have been double vaccinated and had a previous infection (green) or double vaccinated only (orange). Image credit: Sagin et al, AHRI 2021

“Given the very large drop in neutralizing antibody titers that are seen here with Omicron … certainly in my view it would merit pushing forward as fast as possible with making Omicron-specific vaccines,” virologist Dr Jesse Bloom told the New York Times, “as long as it seems like there’s a possibility it could spread widely.”

But despite these grim findings, Sigal is cautiously optimistic. For the group who had a prior COVID-19 infection, the study found, neutralizing antibody titers remained much higher than in the two-dose-only group, making protection “mostly a question of quantity,” he said – that is, he explained, “the more antibodies you [have], the more chance you'll be protected from Omicron.”

That makes vaccines and boosters a priority for us all – and although the lab results suggest current vaccines are beneficial, Pfizer has already suggested a new Omicron-specific version of its vaccine could be ready within the next few months.

“While I think there’s going to be a lot of infection, I’m not sure this is going to translate into systems collapsing,” Sigal told the New York Times. “My guess is that it’ll be under control.”


While anecdotal evidence suggests Omicron may lead to less severe cases of COVID-19, there’s still nowhere near enough evidence to definitively say one way or the other. This is another aspect of the new strain that the team are currently working to understand – and though the confidence intervals “will … likely [be] wide,” Sigal cautioned, they hope to get the first solid data on severe disease incidence by the weekend.

“If I don’t die from the virus,” Sigal told the New York Times, “I’ll die of exhaustion.”


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