Extending time between mRNA COVID vaccine doses may boost efficacy
COVID-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. Among two-dose recipients, 12% received their second dose 3 to 5 weeks after the first, while 31% did so at 6 weeks, and 58% at 7 or more weeks. Over the study period, Canada's National Advisory Committee on Immunization changed recommended dosing intervals, ranging from 3 to 4 weeks to 16 weeks, as conditions evolved.
After adjustment, mRNA VE against infection was 71% for one dose at a median of 7 weeks and 90% for two doses at 13 weeks. Seven months after the second dose, VE was still greater than 80%. Two-dose VE was consistently 5% to 7% higher when given at least 7 weeks apart than after a 3- to 5-week interval.
The study authors said the findings didn't suggest marked waning immunity, even in the Delta era. "Such protection may have been facilitated by the Canadian decision to extend the interval between first and second doses, reinforcing that option in other jurisdictions or for future cohorts in the context of vaccine supply constraints and/or where urgent top-up of already substantial one-dose protection is less pressing," they wrote.
Apr 15 Open Forum Infect Dis study
Worldwide COVID-19 deaths increased 6% on weekends amid pandemic
A global analysis of nearly 6 million COVID-19 deaths over 2 years reveals that 6% more occurred on weekends than on weekdays in all countries except Germany, according to data to be presented at the annual congress of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) Apr 23 to 26 in Portugal.
A University of Toronto researcher led the study, which involved analysis of all global COVID-19 deaths recorded in the World Health Organization (WHO) COVID-19 database from Mar 7, 2020, to Mar 7, 2022. The team also evaluated deaths in the 10 countries with the highest COVID-19 infections: The United States, United Kingdom, France, Germany, Italy, Spain, Russia, India, Brazil, and Canada.
On average, 449 more people (8,532 vs 8,083) died per day on weekends than on weekdays, equivalent to a 6% relative increase (95% confidence interval, 3% to 8%). The highest absolute increases were in Brazil (1,061 vs 823 [29%]), the United States (1,483 vs 1,220 deaths [22%]), Canada (56 vs 48 [17%]), and the United Kingdom (239 vs 215 [11%]). Only Germany saw fewer deaths on the weekends relative to weekdays (137 vs 87 deaths).
The rise was particularly large on Sundays relative to Mondays (8,850 vs 7,219) and Fridays vs Mondays (9,086 vs 7,219).
The study authors said the higher weekend death rate may have been due to lower hospital efficiency, uneven staffing levels, a different mix of personnel expertise, variable hours, reduced capacity, or delays in reporting. "The apparent increased COVID-19 deaths reported on weekends might confound projections and create a false sense of security on subsequent weekdays," they wrote.
The weekend increase was evident throughout the pandemic, regardless of pandemic severity. "What's more, our findings suggest that this problem is not resolving despite improved health system performance and awareness over the course of the pandemic," lead author Fizza Manzoor, MD, said in an ESCMID press release.
She added, "Bureaucratic delays on weekends alone do not explain why there are fewer documented COVID-19 deaths on Mondays compared to Fridays, and reporting lags alone cannot explain why the increase in weekend deaths was so substantial in the USA and not seen in Germany."
Apr 5 study data and poster
Apr 17 ESCMID press release
