Dr. Manjul Shukla transfers Pfizer COVID-19 vaccine into a syringe, Thursday, Dec. 2, 2021, at a mobile vaccination clinic in Worcester, Mass. AP
Omicron has caused global concern over signs that it can transmit faster than previous strains and fears that its multiple mutations could help it evade immune defences provided by vaccines. No deaths have so far been associated with the variant.
In preliminary results published on Wednesday, Pfizer and BioNTech said their vaccine "is still effective in preventing Covid-19, also against Omicron, if it has been administered three times".
But they warned that "the Omicron variant is probably not sufficiently neutralized after two doses".
According to early laboratory research using blood serum from vaccinated people, a booster third dose generated around the same level of antibodies against Omicron as is seen after a second dose with the initial strain.
Blood samples from people who had received two doses of the current vaccine showed on average a 25-fold reduction in neutralizing antibodies compared to the early strain of the virus, the companies said.
But they added that another part of the immune response -- from T cells -- were probably still effective against the variant, adding that "vaccinated individuals may still be protected against severe forms of the disease".
Their results have not been peer-reviewed.
Real World Test
Speaking at a press conference, BioNTech CEO Ugur Sahin said that reducing the time required between second and third doses of the vaccine was the "right way to go" to increase protection through the winter.
The United Kingdom has begun giving booster shots to individuals at least three months after their second dose, while the delay to receive an additional shot is longer elsewhere.
The vaccine-makers said that an Omicron-specific version of the jab, currently in development by BioNTech, would be ready for delivery by March, pending regulatory approval.
The decision to switch production to the tailored vaccine would depend "on the spread of the Omicron variant", the German company's chief operating officer Sierk Poetting said at a press conference.
The announcement comes after other preliminary results from a small study in South Africa suggested there was up to a forty-fold drop in the ability of the antibodies from the Pfizer-BioNTech vaccine to neutralize Omicron, compared to the earlier Beta variant.
The results suggest "that there is definitely much less neutralization against Omicron compared to neutralization against the original strains that came out of Wuhan initially," said Willem Hanekom, executive director of the Africa Health Research Institute, which carried out the study.
But he cautioned that it was important to be "extraordinarily careful" interpreting the results because they only reflect a laboratory setting.
"What we need is real-world results of what is happening out there," he told AFP.
Omicron counts more than 30 mutations on the spike protein that dots the surface of the coronavirus and allows it to invade cells.
Given the array of changes in this strain of the virus, Paul Moss, Deputy Head of the College of Medical and Dental Sciences at the University of Birmingham, said this kind of result "was not unexpected".
However, he said, "emerging evidence from booster vaccinations shows that they are capable of generating very high levels of antibody which should potentially still provide valuable protection against infection".
The detection of the first Omicron cases two weeks ago coincided with soaring infection numbers across the world, and the variant added fuel to concerns about a global Covid resurgence.
Dozens of nations have re-imposed border restrictions in response to the spread of the new virus variant and raised the possibility of a return of economically punishing lockdowns.
Omicron has so far been found in 57 countries, the WHO said.