New data indicates two doses of Pfizer and BioNTech’s mRNA COVID-19 vaccine may not be sufficient to protect from the SARS-CoV-2 Omicron variant. However, a third dose was seen to raise neutralizing antibody levels up to those seen with two doses against the original strain of the novel coronavirus.
As cases of Omicron continue to be detected in countries all over the globe scientists are racing to understand what kind of threat this variant poses to our vaccine protection. Over the last 24 hours some of the first laboratory data has been announced revealing the effects of vaccine-induced antibodies against Omicron.
A press release from Pfizer and BioNTech announced the results of preliminary experiments testing antibodies in blood samples from vaccinated subjects against a pseudo Omicron virus engineered to mimic its uniquely mutated spike protein. The research focused on the response of neutralizing antibodies to Omicron. These antibodies are not the only immune cells generated by vaccines to fight back against SARS-CoV-2 but they are generally known to be the first line of defense protecting a person against initial infection.
The Pfizer data reveals a 25-fold reduction in neutralizing antibody response to Omicron in blood samples from those receiving two doses of its mRNA vaccine, compared to the antibody response seen against the original SARS-CoV-2 spike protein. The good news in the Pfizer data is that this reduction in neutralizing antibody response was seen to almost completely recover after a booster, rising 25-fold in blood samples from individuals following three vaccine doses.
Another encouraging sign in the Pfizer data is the finding that immune T-cells generated by the vaccine are mostly unaffected by the mutations seen in Omicron. In fact, the company estimates vaccine-induced T-cells will still recognize around 80 percent of the spike protein in the Omicron variant.
T-cells are the immune system’s serious soldiers. Unlike antibodies, which can jump into action quickly and prevent a virus from infecting a host in the first place, T-cells take a little longer to catch up with a virus. And it is T-cells that play a major role in preventing an infection progressing from mild to severe. So this early data indicates current vaccines should still hold up well against the Omicron variant in terms of preventing severe disease, especially after a third dose.
“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,” explains Pfizer CEO Albert Bourla. “Ensuring as many people as possible are fully vaccinated with the first two dose series and a booster remains the best course of action to prevent the spread of COVID-19.”
Eleanor Riley, an immunologist from the University of Edinburgh, says the new data is reassuring but affirms the importance of third-dose vaccine programs. While two doses of mRNA vaccines may help prevent severe disease it may not be sufficient to prevent infection and transmission, Riley notes. So Omicron makes a third vaccine dose absolutely vital if the pandemic is to be brought under control.
“Not only does a booster vaccination provide strong antibody-mediated neutralization of Omicron but also the vast majority of the sites in the spike protein that activate T cells are conserved between Omicron and the vaccine strain,” says Riley. “This suggests that a booster should provide high levels of protection against infection and severe disease.”
Another recent Omicron antibody study from scientists in South Africa reported similar findings to Pfizer. Led by Alex Sigal from the African Health Research Institute, the small study looked at how Omicron fared in blood samples from 12 people. Six of the subjects were two-dose vaccinated with Pfizer and six were two-dose Pfizer vaccinated alongside experiencing a COVID-19 infection early in 2020.
Overall, Sigal’s research saw on average a 41-fold reduction in neutralizing antibody response against Omicron compared to an early strain of the virus. The promising news in Sigal’s data, however, was five of the six subjects previously infected with COVID-19 maintained high levels of antibody neutralization against Omicron.
This study did not investigate antibody responses after three vaccine doses but the researchers speculate the strong neutralization response seen in blood samples from two-dose + prior infection subjects should hypothetically be mirrored after three vaccine doses.
It is important to note these are just lab studies and do not offer insights into how the Omicron variant will behave in real-world scenarios. These antibody studies also cannot help us understand whether or not Omicron leads to more severe disease compared to prior variants.
What this data does suggest is that Omicron is likely to lead to greater rates of breakthrough infections in two-dose vaccinated people. In a blog post, Eric Topol, director of the Scripps Research Translational Institute, discusses the current Omicron findings, indicating it is too early to know whether this variant is more lethal than prior variants.
“Early reports from South Africa indicated the possibility that cases were more mild, requiring less hospitalizations and oxygen supplementation,” Topol points out. “But the population assessed was predominantly young, had prior COVID, or were vaccinated. We can hope this is the case but will not really know the answer to this question until much larger numbers of people aged 60 plus, those without prior infection, or vaccination, or several months out from vaccination, are studied. Fortunately, there are no data to suggest Omicron is associated with more lethality or severe COVID than prior variants.”
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