Three doses of the Pfizer/BioNTech vaccine are likely to protect against infection with the Omicron variant but two doses may not, according to laboratory data that will increase pressure to speed up booster programmes.
Tests using antibodies in blood samples have given some of the first insights into how far Omicron escapes immunity, showing a stark drop-off in the predicted protection against infection or any type of disease for people who have had two doses. The findings suggest that, for Omicron, Pfizer/BioNTech should now be viewed as a “three-dose vaccine”.
The vaccine makers said they would continue “at full speed” with plans to develop an updated Omicron-based vaccine by March 2022 if needed – and their working presumption is that it will be.
Separate results, from preliminary studies by the German Centre for Infection Research, also found significant reductions in antibody potency for the Pfizer/BioNTech, Moderna and Oxford/AstraZeneca vaccines against Omicron.
In the first official briefing from vaccine manufacturers on the likely efficacy of their shots against Omicron, Prof Uğur Şahin, the CEO and co-founder of BioNTech, said on Wednesday: “Individuals who have received two vaccines will most likely not have a significant prevention from infection or any type of disease. We know they will have memory T-cells, which may prevent severe disease.”
He added that the strategy adopted by the UK and others to accelerate booster programmes was “the right way to go”, with an extra dose appearing to compensate for the vaccine being less well matched to Omicron than to earlier Covid strains.
Vaccine makers now face the task of deciding whether a tweaked variant jab will be required and what form it should take. This will depend on real-world data on reinfection rates, transmissibility and how severe the Omicron variant is, which will emerge in the next two to six weeks.
Şahin said his company was, for now, working on the development of an Omicron-specific vaccine, but a secondary option was a hybrid Omicron/Delta vaccine, which could be manufactured on a similar 100-day schedule.
Pfizer’s data, posted online on Tuesday, is among the first to be released about the ability of the immune system to combat Omicron and has not been peer-reviewed. The scientists tested blood from 19 people who had the Pfizer/BioNTech jab for its ability to neutralise the Omicron variant, and compared this with the response to an earlier form of coronavirus.
The scientists found a 25-fold reduction in the blood’s neutralisation against Omicron, but not complete immune escape. Blood from people who had received three doses had a roughly equivalent potency against Omicron as blood samples from those who had two doses pitted against the original Wuhan strain.
The findings are broadly in line with a preliminary study from the Africa Health Research Institute in South Africa on Tuesday, which found a 41-fold reduction in the potency of antibodies after two doses of Pfizer against Omicron.
“It is likely that lesser vaccine-induced protection against infection and disease would be the result,” said Prof Willem Hanekom, the executive director of theinstitute. “Importantly, most vaccinologists agree that the current vaccines will still protect against severe disease and death in the face of Omicron infection. It is therefore critical that everyone should be vaccinated.”
Scientists believe that T-cells, which work in parallel with antibodies, are likely to hold up better against Omicron, including protecting against severe disease.
Daniel Altmann, a professor of immunology at Imperial College London, said the study offered a clear message. “Those who are unvaccinated, or even two-dose vaccinated, are likely to be highly vulnerable to infection,” he said. “However, those who’ve seen a spike three times, either by boosting or by infection plus two doses, appear generally in the safety zone … So [there is] an even stronger argument for getting boosters as widely and rapidly as possible.”
Some responded with relief to the initial findings, indicating that things could have been worse. Prof Jonathan Ball, a professor of molecular virology at the University of Nottingham, said that while the dataset was small, it was reassuring. “We need to understand whether these increased virus-killing antibody levels after boost plays out for all age groups, but these early signs are good,” he said.
Speaking on Wednesday, the World Health Organization’s director general, Tedros Adhanom Ghebreyesus, said its advisory group on vaccines was also investigating whether changes to current vaccines were needed. There was now a consistent picture of rapid increase in transmission due to the Omicron variant, though the exact rate remained difficult to quantify, he said.