First study of omicron shows Pfizer vaccine may be less effective

The omicron variant of the coronavirus partially evades antibody immunity from two doses of the Pfizer-BioNTech vaccine, according to initial data from South Africa published Tuesday.

The small study of 12 patients conducted by the Africa Health Research Institute found there was about a 40-fold reduction in vaccine-induced neutralizing antibodies compared to the ancestral strain of the virus.

Six of the 12 people were previously infected with COVID-19 during South Africa’s first wave.

However, the study showed that people with previous infection who had also gotten vaccinated had considerably higher levels of antibodies. 

The study did not include people who received booster doses, but some health experts said the protection levels from a booster could mimic a previous infection after vaccination.

The data are some of the first to emerge about the omicron variant, which was identified by South Africa less than two weeks ago. The results were posted online but have not been peer reviewed.

This study was small, and there will be more data coming from other studies, which will help experts form a broader picture of the impact of the new variant. Anthony Fauci, the nation’s top infectious diseases doctor, said Tuesday he expects it will take until at least next week before information about vaccine effectiveness is understood.

“The clinical implications of these important laboratory data need to be determined. It is likely that lesser vaccine-induced protection against infection and disease would be the result,” Africa Health Research Institute Executive Director Willem Hanekom said in a statement. 

“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,” Hanekom said.

Experts have predicted that the omicron variant would likely lead to some drop in neutralizing antibodies, because of the large number of mutations on the virus. The results aligned with that theory, but also showed that protection wasn’t totally lost. Vaccinated people who received a booster may still get infected, but won’t be severely ill.

“Not great. Not terrible,” tweeted Ashish Jha, dean of the Brown University School of Public Health. 

Additionally, a drop in neutralizing antibodies found in blood samples may not reflect how the variant may behave in a real world setting. Neutralizing antibodies are just one component of protection, and do not necessarily correspond to vaccine effectiveness.