COVID-19 vaccine effectiveness against Omicron variant

Editor's Note

This study from the UK finds that primary immunization with two doses of COVID-19 vaccine provided limited protection against the Omicron variant. A booster substantially increased protection, but that waned over time.

Included in the analysis are 886,774 Omicron variant infected patients, 204,154 Delta variant infected patients, and 1,572,621 test-negative control patients.

Among the findings:

• At all time points and for all combinations of primary and booster vaccines (ie, Pfizer-BioNTech, AstraZeneca, Moderna) investigated, vaccine effectiveness against symptomatic disease was higher for the Delta than the Omicron variant.
• After two doses of the AstraZeneca vaccine, there was no effect against Omicron noted after 20 weeks.
• Vaccine effectiveness after two doses of the Pfizer-BioNTech vaccine was 65.5% at 2 to 4 weeks, dropping to 8.8% at 25 weeks or more.
• Among AstraZeneca primary course recipients: Vaccine effectiveness increased to 62.4% at 2 to 4 weeks after a Pfizer-BioNTech booster, before decreasing to 39.6% at 10 or more weeks. Vaccine effectiveness increased to 70.1% at 2 to 4 weeks after a Moderna booster and decreased to 60.9% at 5 to 9 weeks.
• Among Pfizer-BioNTech primary course recipients: Vaccine effectiveness increased to 67.2% at 2 to 4 weeks after a Pfizer-BioNTech booster, before declining to 45.7% at 10 or more weeks. Vaccine effectiveness increased to 73.9% at 2 to 4 weeks after a Moderna booster and fell to 64.4% at 5 to 9 weeks.

The researchers conclude that two doses of vaccination with AstraZeneca or Pfizer-BioNTech vaccine are insufficient to provide adequate levels of protection against the Omicron variant. A Pfizer-BioNTech or Moderna booster after the AstraZeneca or Pfizer-BioNTech primary course substantially increased protection, but that protection waned over time.