Two New Studies — And Pfizer — Confirm mRNA Vaccines Are Less Effective on Omicron

December 9, 2021

The Pfizer/BioNTech and Moderna COVID-19 vaccines are 25-40 times less effective against the new Omicron variant than the original strain and Delta variants, two new laboratory studies have found.

Studies from South Africa and Germany used serum from subjects with varying levels of vaccination to test vaccine efficacy. In a South African study of 14 samples, the Pfizer vaccine was 41 times less effective against Omicron than the original Wuhan strain. The German study determined that the Moderna vaccine was 24.5-fold times less effective and the Pfizer vaccine up to 30 times less effective against Omicron than Delta.

Both studies did confirm that the Omicron variant still uses the ACE2 receptor to get into cells. This is good news, according to Alex Sigal, of the Africa Health Research Institute. Primary author on the South African paper, Sigal tweeted this reply in a discussion thread.

“… this was better than I expected of Omicron. The fact that it still needs the ACE2 receptor and that escape is incomplete means it’s a tractable problem with the tools we’ve got.”

Both studies are published on Medrxiv, a preprint server that allows researchers to post non-peer reviewed data. So neither paper has been edited for clarity or reviewed for data accuracy. And because they’re in vitro lab studies, they don’t reflect real-world data.

Jonathan Ball, professor of molecular virology at the University of Nottingham, cautioned against over-interpreting the data, in a comment on the website of the UK-based Science Media Centre.

“While the amount of virus killing observed in the lab is reduced markedly there is still measurable virus neutralization, especially in those who were vaccinated and previously infected. The other thing to remember is that many of the vaccines also generate T cell immunity and we think that this will be less impacted by the high level of mutations that omicron has. I am still confident that the vaccines, especially after a boost, will still protect from serious disease. That’s why we still need to get the message across, get vaccinated, get boosted, even if you have been infected before.”

Pfizer has also posted its own data, confirming that two doses of its vaccine are about 25 times less effective on Omicron than other variants, but that a third booster improves the coverage.

“[T]wo doses may not be sufficient to protect against infection with the Omicron variant,” the company said. “[We] believe that vaccinated individuals may still be protected against severe forms of the disease and are closely monitoring real world effectiveness against Omicron, globally.”

The South African study tested 14 plasma samples from 12 subjects fully vaccinated with the Pfizer vaccine. Six patients had been infected with the Wuhan strain.  Those samples showed very strong neutralization of that virus. But the neutralization ability against Omicron was 41 times lower than it was against Wuhan.

The German study also showed decreased efficacy in the Pfizer vaccine, and similar results in serum from Moderna-vaccinated subjects. The number of subjects included in this study isn’t clear in this paper; the information is apparently included in a supplementary index, which is not posted on the preprint site.

In subjects who had received two Moderna vaccines, efficacy against Omicron was 20 times lower than it was against Delta. Efficacy was 22.7 times lower in samples from Moderna double-vaccinated subjects who had gotten a Pfizer booster.

Some subjects in this study had been double-vaccinated with a combination of the Pfizer vaccine and the weakened whole-virus ChAdOx1 nCoV-19 vaccine. In these samples, there was no efficacy against Omicron. The addition of a Pfizer booster did improve coverage, but overall, that combination was still 27 times less effective against the new variant.

The German study also looked at serum from an undetermined number of subjects fully vaccinated with the Pfizer vaccine. In double-vaccinated samples, efficacy was 11.4 times lower compared to Delta. In double-vaccinated, boosted samples efficacy was 37 times lower at 2 weeks after boosting and 24.5 times lower at 3 months after boosting.

Read the South African study here: bit.ly/3pBEaVv.

Read the German study here: bit.ly/33ebCtC. — Michele G. Sullivan