This is a summary, written by members of the CITF Secretariat, of:

Grunau B, Asamoah-Boaheng M, Lavoie PM, Ehsanul Karim M, Kirkham T, Demers PA, Barakauskas V, Citlali Marquez A, Jassem AN, O’Brien SF, Drews SJ, Haig S, Cheskes S, Goldfarb DM. A Higher Antibody Response is Generated with a 6 – 7 Week (vs Standard) SARS-CoV-2 Vaccine Dosing Interval. Clin Infect Dis. 2021, 30 Nov; doi: 10.1093/cid/ciab938.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

New evidence stemming from a CITF-funded study of Canadian paramedics shows that getting two doses of an mRNA vaccine 6-to-7-weeks apart produces higher levels of antibodies compared to two doses 3-to-4-weeks apart, as recommended by the manufacturers. The research, published in Clinical Infectious Diseases, was led by Drs. Brian Grunau and David Goldfarb from the University of British Columbia. 

The COVID-19 Occupational Risks, Seroprevalence, and Immunity among Paramedics (CORSIP) study seeks to identify COVID-19-related occupational risks among paramedics in Canada and evaluate their immunity to SARS-CoV-2.

Key findings:

  • Paramedics who received an mRNA vaccine with the two doses six to seven weeks apart had significantly higher anti-spike antibodies after the second dose compared to those vaccinated with a shorter interval;
  • Results were consistent whether evaluating antibody levels after either Pfizer or Moderna vaccines;
  • The findings indicate that delayed vaccine intervals (i.e., more than 21 to 28 days between doses) may be beneficial in terms of the antibody response generated after completion of the series;
  • This may be informative for countries with vaccine supply issues and provide a rational for increasing the number of individuals receiving first vaccine doses while delaying the second dose past 28 days.

The recent article analyzed blood samples from 186 CORSIP-enrolled paramedics who had either received two doses of Pfizer-BioNTech’s Comirnaty mRNA vaccine (70.4%), Moderna’s Spikevax mRNA vaccine (29.6%), or a combination of both (0.54%). Participants with a previous documented SARS-CoV-2 infection were excluded.

Participants were categorized based on the interval between vaccine doses: a short interval was defined as 21 to 28 days between doses (as recommended by Pfizer and Moderna, respectively); a long interval ranged from 42 to 49 days between doses.

Antibody responses to SARS-CoV-2’s spike protein were assessed using two different serological tests. The median age of the participants was 38, 45% were women, and approximately 15% self-identified as part of a racialized group.

Learn more about the CORSIP study here.