Study: Pfizer Vaccine Less Effective Against Omicron Variant

The South Africa study shows a 41-fold drop in Pfizer vaccine’s neutralisation of Omicron, but considerable protection is retained in those who were both double vaccinated and previously infected with Covid-19.

KUALA LUMPUR, Dec 8 — The first lab study on neutralisation of Omicron shows that the Covid-19 variant, with a large number of mutations on the spike protein, evades protection from Pfizer-BioNTech’s vaccine.

However, “considerable” immunity is retained in people who were both vaccinated with two doses and previously infected, according to the preliminary study from Africa Health Research Institute (AHRI) in South Africa published yesterday.  

This study tested 14 plasma samples from 12 individuals who were double vaccinated with two doses of Pfizer’s mRNA vaccine. Of them, six individuals had no previous record of coronavirus infection, while another six were previously infected with D614G during the first Covid-19 wave in South Africa.

The study revealed a huge 41-fold decline in neutralising antibodies against Omicron compared to the ancestral D614G virus. Neutralising antibody levels dropped from 1,321 for the D614G virus to just 32 for Omicron. 

But Omicron was unable to completely escape vaccine-induced immunity as five of the double vaccinated participants, who were all previously infected with Covid-19, showed “relatively high” neutralisation titers with the new variant of concern. 

“New work from AHRI’s @sigallab strongly suggests that the SARS-CoV-2 #Omicron variant escapes antibody immunity induced by the Pfizer vaccine, but that considerable immunity is retained in people who were both vaccinated & previously infected,” AHRI said on Twitter

Corresponding author Alex Sigal, a professor at AHRI, explained on Twitter that the Omicron variant of concern was unable to completely escape protection from Pfizer’s vaccine, as “previous infection + vaccination still neutralises”.

“These results are better than I expected. The more antibodies you got, the more chance you’ll be protected from Omicron,” Sigal added.

In an online presentation of the findings of his study, Sigal noted that more breakthrough cases will be recorded among vaccinated individuals as the loss of immune protection is “robust”.

“A good booster probably would decrease your chance of infection, especially severe infection leading to more severe disease,” Sigal was quoted as saying.

“People who haven’t had a booster should get one, and people who have been previously infected should be vaccinated.”

AHRI executive director Professor Willem Hanekom, one of the study co-authors, said Covid-19 vaccines would likely be less effective against infection and disease from Omicron. 

“Importantly, most vaccinologists agree that current vaccines will still protect against severe disease and death in the face of Omicron infection,” he said in a statement.

“It’s therefore critical that everyone should be vaccinated.”

Sigal said the findings from this first set of data may change when the team carries out more experiments.

The study did not include individuals vaccinated with other Covid-19 vaccines and individuals who received booster shots besides their primary vaccination series.

It is to be noted that the report, which was published online, has not been peer-reviewed.

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