Extending time between mRNA COVID vaccine doses may boost efficacyCOVID-19 mRNA vaccine effectiveness (VE) against infection was 5% to 7% higher when the two primary doses were given at least 7 weeks rather than 3 to 5 weeks apart, according to an observational study of hospital and community healthcare workers (HCWs) in British Columbia published late last week in Open Forum Infectious Diseases.Researchers from the BC Centre for Disease Control, Communicable Diseases and Immunization Services used a test-negative design to evaluate the odds of vaccination in HCWs and controls matched in a 6:1 ratio to COVID-19 test date.
mRNA vaccination was considered receipt of the first dose 21 or more days before the test date or the second dose at least 14 days before.Tests were conducted from Jan 17 to Oct 2, 2021, a span that included the dominance of the Delta variant.
Mean follow-up was 49 days for the single-dose group and 89 days for two-dose recipients. Over 80% of HCWs were women, and controls were about a decade older than cases.
Among vaccinated HCWs, 92% of single-dose and 83% of two-dose recipients were given the Pfizer/BioNTech COVID-19 vaccine.Of all vaccinees, 1,265 received one dose of COVID-19 vaccine, while 1,246 received two.