COVID-19 vaccine boosters lower the risk of death among adults with multiple chronic conditions by more than 90% and increase protection against emergency department (ED) or urgent care (UC) visits among children aged 5 to 11 years by 77%, two new Omicron variant studies find.
In CMAJ, a team led by University of Hong Kong researchers compared the death rate among adults with at least two chronic conditions who received two or three Pfizer/BioNTech or Sinovac COVID-19 vaccine doses from November 2021 to March 2022.
The team followed 120,724 Pfizer recipients (including 87,289 booster recipients) for a median of 34 days and 127,318 Sinovac recipients (including 94,977 booster recipients) for a median of 38 days.
Among Pfizer recipients, booster recipients were 95% less likely to die of COVID-19 than two-dose recipients (5 vs 34 deaths; weighted incidence rate ratio [IRR], 0.05). Similarly, Sinovac booster recipients had a 92% lower risk of death than two-dose recipients (26 vs 88 deaths; weighted IRR, 0.08).
In a CMAJ news release, senior author Esther Chan, PhD, of the University of Hong Kong, said the results "support the effectiveness of booster doses of vaccines of 2 different technological platforms."
Third dose upped protection to 77%
In a study in the Journal of the Pediatric Infectious Diseases Society, a team led by Kaiser Permanente Southern California researchers estimated the protection of two or three doses of the Pfizer vaccine against Omicron-related ED and UC visits among children aged 5 to 11 years with respiratory infections from November 2021 to September 2022.
The 1,992 COVID-infected children were compared with 1,992 non-COVID controls using a test-negative design. Estimated effectiveness of two doses against ED or UC visits was 60% up to 3 months before waning to 28%; a booster increased protection to 77%.
"Despite protection against COVID-19 afforded by vaccination in children 5-11 years of age, vaccine uptake in this age group remains considerably lower than that observed in older populations," the authors wrote.