Live updates: follow the latest news on Covid-19 variant Omicron
Omicron significantly reduces the ability of antibodies generated by two doses of the Pfizer-BioNTech vaccine to neutralise the variant, a small study has found.
The laboratory tests suggest there is a “very large” drop in neutralisation of Omicron by the vaccine, relative to the original virus.
But escape is not complete, researchers said, meaning antibodies produced by the vaccine will retain some protection against the strain.
The pre-print study, which has not been reviewed yet, was carried out by South African scientists at the Africa Health Research Institute, who tested blood samples of 12 people previously vaccinated with two doses of Pfizer-BioNTech.
They found a 41-fold drop in the ability of the antibodies to neutralise the variant.
Lead researcher Prof Alex Sigal said previous infection plus vaccination still neutralises the strain.
“Omicron escape from BNT162b2 [Pfizer-BioNTech] neutralisation is incomplete,” he tweeted.
“Previous infection + vaccination still neutralises.”
Experts said the “clinical implications” of the data need to be determined.
“It is likely that lesser vaccine-induced protection against infection and disease would be the result,” said Africa Health Research Institute executive director, professor Willem Hanekom.
“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.”
The results are in line with an earlier estimate of a 25 to 60-fold drop in the ability of antibodies to neutralise the virus.
Experts said the predictions were not a surprise given the high number of mutations in Omicron.
“Even if Omicron is also more infectious, the main driver of increased transmission is probably immune escape,” Paul Hunter, an infectious diseases specialist and professor in medicine at the University of East Anglia in the UK, told The National.
“This fits with what we are seeing in South Africa and globally about the rapid spread and the marked increase in reinfections.”
Immunologists said the predictions underscore the importance of receiving vaccine booster shots to bolster protection against the new strain.
“It’s likely the effect of antibodies will drop but quantity (eg after a booster) can trump quality when it comes to antibodies and the T cell response might also help protect against severe disease,” Luke O’Neill, professor of biochemistry in the School of Biochemistry and Immunology at Trinity College Dublin, told The National.
“The data from South Africa do indeed suggest mild disease but again we need more information especially around the age profile.
“We still don’t know the risk of Omicron for older people but again if they are boosted there may be protection.”
BioNTech’s chief executive earlier sought to allay fears about the Omicron coronavirus variant, saying the Pfizer vaccine will probably offer a robust defence against severe disease.
Ugur Sahin, who is also co-founder of the drug giant, said people should not “freak out” about the latest variant that has sent governments rushing to impose travel restrictions.
He said that even though the highly mutated variant could result in more vaccinated people becoming infected with the virus, it will probably be targeted by immune cells.
Hospital admissions have climbed in all provinces in South Africa, with 135 people admitted in hardest-hit Gauteng alone on Tuesday, 38 more people in the ICU, and an additional 10 people placed on ventilators.
Across the country in the past week, 1,384 people were admitted, 120 to the ICU, and 22 more people were placed on ventilators.