Effectiveness of COVID-19 vaccines and booster dose against the Omicron variant

Concerns about the effectiveness of current COVID-19 vaccines have arisen due to a rapid increase in COVID-19 cases caused by the Omicron variant of SARS-CoV-2, even in highly vaccinated populations. A new study, funded by the UK Health Security Agency, used a test-negative case-control design to estimate COVID-19 vaccine effectiveness against symptomatic disease caused by the Omicron (B.1.1.529) and Delta (B.1.617.2) variants in England. Vaccine effectiveness was determined after primary immunization with two doses of the Pfizer/BioNTech, AstraZeneca or Moderna vaccine and after a booster dose of one of these vaccines (given at least 175 days after the second vaccine dose). The study, conducted from Nov. 27, 2021 to Jan. 12, 2022, included a total of 886,774 persons infected with the Omicron variant, 204,154 persons infected with the Delta variant, and 1,572,621 test-negative controls. Read: Vaccines against Sars-CoV-2 lose effectiveness in preventing infection after several months Results showed that vaccine effectiveness against symptomatic disease was higher for the Delta variant than for the Omicron variant at all measured time points and for all combinations of primary course and booster dose vaccines. Specific findings are highlighted below. Efficacy against Omicron variant after primary series (two doses): No effect against the Omicron variant was seen at 20 weeks after two doses of the AstraZeneca vaccine. Vaccine effectiveness after two doses of Pfizer/BioNTech vaccine was 65.5% at two to four weeks, dropping to 15.4% after 15 to 19 weeks, and further declining to 8.8% at 25 or more weeks. Vaccine effectiveness after two doses of Moderna vaccine was 75.1% after two to four weeks, dropping to 25.3 after 15 to 19 weeks, and further declining to 14.9% after 25 or more weeks. Read: Single-dose Janssen COVID-19 vaccine less effective than two-dose Pfizer vaccine Efficacy against Omicron variant after booster dose: Vaccine effectiveness was lowest among those who received a primary course series of AstraZeneca vaccine followed by an AstraZeneca vaccine booster. Vaccine effectiveness against the Omicron variant was 55.6% at two to four weeks after the booster dose, declining to 46.7% at five to nine weeks. For AstraZeneca vaccine primary course recipients, vaccine effectiveness increased to 62.4% at two to four weeks after a Pfizer/BioNTech booster dose, decreasing to 52.9% at five to nine weeks, and 39.6% at 10 or more weeks. Vaccine effectiveness after an AstraZeneca primary course increased to 70.1% at two to four weeks after a Moderna vaccine booster, then decreased to 60.9% at five to nine weeks. For Pfizer/BioNTech primary course recipients, vaccine effectiveness increased to 67.2% at two to four weeks after a Pfizer/BioNTech booster, then declined to 55.0% at five to nine weeks, and 45.7% at 10 or more weeks. After a Pfizer/BioNTech primary course, a Moderna vaccine booster increased vaccine effectiveness to 73.9% at two to four weeks, then fell to 64.4% at five to nine weeks. After a Moderna vaccine primary course, vaccine effectiveness increased to 64.9% at two to four weeks after a Pfizer/BioNTech booster. No data were provided on vaccine effectiveness beyond four weeks. After a Moderna vaccine primary course, vaccine effectiveness increased to 66.3% at two to four weeks after a Moderna booster. No data were provided on vaccine effectiveness beyond four weeks. The authors conclude that primary immunization with two doses of AstraZeneca, Pfizer/BioNTech or Moderna vaccine provided limited protection against symptomatic disease caused by the Omicron variant. A booster dose of Pfizer/BioNTech or Moderna vaccine after a primary course of AstraZeneca or Pfizer vaccine substantially increased protection, but that protection also waned over time. Read: One in five adolescent girls with type 2 diabetes have PCOS The authors note that their study was unable to determine protection against severe forms of disease because of the small number of Omicron cases resulting in hospitalization. However, they stress that two doses of Pfizer/BioNTech or AstraZeneca vaccine are insufficient to provide protection against infection with the Omicron variant and mild disease. Giving a booster dose of Pfizer/BioNTech or Moderna vaccine provides a substantial increase in protection against mild disease, although protection wanes over time. These findings support maximizing coverage with a third (booster) dose of an mRNA vaccine in populations that have received two doses of the AstraZeneca, Pfizer/BioNTech or Moderna vaccine. Reference 1. Andrews N, Stowe J, Kirsebom F, et al. Covid-19 vaccine effectiveness against the Omicron (B.1.1.529) variant. NEJM 2022; published online March 2, 2022. https://www.nejm.org/doi/full/10.1056/NEJMoa2119451?query=TOC (accessed March 7, 2022).

Effectiveness of COVID-19 vaccines and booster dose against the Omicron variant

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