Lauren Dempsey, MS in Biomedicine and Law, RN, FISM News 

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Last week a study from the UK was published revealing important information on vaccine efficacy against the Omicron variant. The data, released days before Christmas, disclosed that the effectiveness of Pfizer-BioNTech’s booster shot wanes substantially after just 10 weeks. 

The study carried out by the UK Health Security Agency showed that individuals that had received three doses of Pfizer-BioNTech’s COVID-19 vaccine had waning levels of immunity to protect against symptomatic illness. Specifically, researchers saw levels of vaccine efficacy drop from 70% to 45% within 10 weeks.

The study analyzed 147,597 Delta cases and 68,489 Omicron cases from Nov. 27 through Dec. 17, with individuals who had reported foreign travel being excluded from the study. Vaccination rates were evaluated from both positive and negative PCR test results.

The results show that the average age of infection occurred in individuals aged 20-29, but hospitalization occurred more in individuals 40 years and older (56% of incidents) and individuals over the age of 70 (25% of incidents). The data from the study also seems to confirm what many had already believed – that hospitalization rates from Omicron infections are much lower than Delta infections.

For individuals who were hospitalized from Omicron, 12% had received a booster shot, 56% had received a second dose of vaccine, and 20% were unvaccinated. Individuals who only had one dose of a COVID-19 vaccine were included in the unvaccinated category. Researchers are cautioning that this data is preliminary due to the small numbers of Omicron cases, however it seems to suggest that vaccine efficacy is significantly lower for symptomatic Omicron infection. Vaccine efficacy begins to wane after a second dose and by week 10 is as low as 35% effective. 

The study compared the vaccine effectiveness after initial vaccination and the booster shot for Pfizer-BioNTech, Moderna, and AstraZeneca COVID-19 vaccines. In each category, including Pfizer-BioNTech and Moderna boosters, vaccine effectiveness was much lower for Omicron when compared to Delta. 

Among individuals who received an AstraZeneca vaccine as the primary dose, vaccine effectiveness was around 60% 2 to 4 weeks after receiving a Pfizer or Moderna booster, however by 10 weeks after a booster shot, efficacy dropped to 35% with a Pfizer booster and 45% with a Moderna booster. 

In individuals who received a Pfizer-BioNTech vaccine as the primary dose, vaccine effectiveness was around 70% after a Pfizer -BioNTech booster dose and dropped to a 45% effective rate after 10 weeks. Moderna boosters showed the most durability in this study, with an efficacy rate of 70 to 75% 9 weeks after a booster shot.  

This information comes as health experts are considering if a fourth booster shot is necessary. Israel is currently testing  a second round of boosters among healthcare workers and vulnerable populations. Pfizer’s CEO, Anthony Bourla has said that he believes a third and possibly fourth dose of vaccine will be necessary to offer protection against COVID, saying “when we see real-world data, will determine if the omicron is well covered by the third dose and for how long. And the second point, I think we will need a fourth dose.”

Dr. Anthony Fauci so far has said that he thinks that it is too early to determine if Americans will need a fourth dose of COVID-19 vaccines. He does, however, continue to encourage vaccinations and booster shots, saying “but from the standpoint of if you want to be optimally protected, no doubt, you should get boosted.”