WASHINGTON, United States — COVID-19 vaccines and boosters continued to have very high efficacy against severe outcomes during the Omicron wave of the virus, a large real-world study from the US Centers for Disease Control and Prevention (CDC) showed Friday.
The paper evaluated data from more than 300,000 visits to emergency departments, urgent care clinics, and hospitalizations across 10 states from Aug. 26, 2021 to Jan. 5, 2022.
During the period when the Delta variant was dominant, vaccine efficacy against COVID-19 hospitalization was 90% between 14-179 days after dose two of a vaccine, fell to 81% more than 180 days after the second dose, and rose to 94% 14 days or more after dose three.
After Omicron became dominant, the vaccine efficacy estimate against hospitalization between 14-179 days after dose two was 81%, 57% after more than 180 days from dose two, and 90% 14 or more days after dose three.
A second CDC paper, based on data from 25 US state and local jurisdictions, found that vaccine efficacy against infection waned from 93% prior to Delta to around 80% when Delta became dominant, but protection against death remained stable and high at 94%.
Vaccine efficacy against infection fell to 68% by the time Omicron emerged. The authors weren't able to derive an estimate for vaccine efficacy against death during Omicron, because of a lag in reporting, but the broad scientific expectation is that it will remain very high.
The paper also showed that while deaths among fully vaccinated people rose sharply during the Delta wave -- totaling more than 20,000 people between July to November -- unvaccinated people were still 16 times more likely to die during the same period.
Protection was even greater for people who were boosted. Between October to November, unvaccinated people were around 50 times more likely to die from COVID-19 than people who were vaccinated and boosted.