Extending the interval between COVID-19 vaccine doses was introduced in Canada to accelerate population coverage with a single dose. In research published in JAMA, Drs. Brian Grunau, David Goldfarb, and Pascal Lavoie from the University of British Columbia studied the vaccine-induced antibody levels in paramedics enrolled in a CITF-funded study who were immunized with mRNA vaccines at differing dosing intervals. They show that longer durations between doses led to increased average antibody levels and higher neutralization potential. The “gain” in antibody levels with increasing the vaccine dosing interval was particularly advantageous for the Delta variant.

Within this study, the COVID-19 Occupational Risks, Seroprevalence, and Immunity among Paramedics (CORSIP) study team conducted two investigations. The first investigation used samples collected, on average, 56 days after the second vaccine dose. Within that subgroup, participants received 2 vaccine doses following a short ( 28 days, N=30) or medium (42-49 days, N=30) interval between vaccine doses. The second investigation used samples collected at a set timeframe of 180 (10) days after the first vaccine dose. Within that subgroup, participants received 2 vaccine doses following a short ( 36 days, N=30) or long (100-120 days, N=30) interval between doses. Individuals previously infected with SARS-CoV-2 were excluded.

Key findings:

  • Paramedics who received two mRNA vaccine doses 28 or 36 days apart showed markedly less virus neutralization compared to those who received two mRNA vaccine doses according to medium (42-49 days) or long (100-120 days) vaccine dosing intervals.
  • Shorter vaccine dosing intervals were associated with lower antibody levels against the viral spike protein and receptor-binding domain (RBD), compared to medium or long intervals.
  • Compared to longer intervals (100-120 days), shorter intervals (21-36 days) were associated with decreased blocking binding of the Alpha, Beta, Gamma, and Delta variants onto the cellular receptor ACE2, a key step in viral infection.
  • Compared to medium intervals (42-49 days), shorter intervals (21-28 days) were associated with decreased blocking of the binding of the Delta variant onto the cellular receptor ACE2.

Learn more about the CORSIP study here.

Grunau B, Goldfarb DM, Asamoah-Boaheng M, Golding L, Kirkham TL, Demers PA, Lavoie PM. Immunogenicity of extended mRNA SARS-CoV-2 vaccine dosing intervals. JAMA. 2021 Dec 3, 2021. doi:10.1001/jama.2021.21921