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

Asamoah-Boaheng M, Goldfarb D, Prusinkiewicz M, Golding L, Karim M, Barakauskas V, Wall N, Jassem A, Marquez A, MacDonald C, O’Brien S, Lavoie P, Grunau B. Determining the optimal SARS-CoV-2 mRNA vaccine dosing interval for maximum immunogenicity. bioRxiv 2022.03.01.482592; doi:

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

This pre-print study, not yet peer-reviewed, led by CITF-funded researcher Dr. Brian Grunau from the University of British Columbia, aimed to identify the optimal interval between mRNA vaccine doses to generate the maximum immune response. The research team found that 73 days or more between doses was associated with a higher concentration of antibodies than a short interval (defined as 30 days or less).

Overall, 83% of participants received two doses of the Pfizer-BioNTech Comirnaty vaccine and 17% received two doses of Moderna’s Spikevax. Dosing intervals were classified as “short” (≤30 days), “moderate” (31-38 days), “long” (39-73 days), and “longest” (≥74 days).

Key findings:

  • All measures of immunogenicity increased with longer dosing intervals.
  • Similar results were observed for both Pfizer and Moderna mRNA vaccines.
  • Compared to the “short” interval, the “moderate”, “long” and “longest” intervals were associated with an increase in total anti-spike antibody concentration.
  • When looking at anti-spike and anti-RBD IgG results, the “long” and “longest” intervals were significantly associated to increased concentrations compared to the “short” interval.
  • When looking at binding inhibition between ACE-2 and spike proteins (for the wild type SARS-CoV-2 and Delta variant, longer intervals were associated with higher inhibition compared to the “short” interval.

The researchers followed a cohort of 564 paramedics working in British Columbia, Ontario, Saskatchewan and Manitoba. Paramedics were included in the present study if: they had had two doses of either Pfizer or Moderna vaccines, provided a blood sample 6-months (170-190 days) after the first vaccine, had no evidence of a previous SARS-CoV-2 infection, and had their second dose less than 130 days after the first (to allow for more than 40 days between vaccination and blood sample). The mean age of study subjects was 40 years and 45% were female.

Blood samples were tested for anti-spike and anti-RBD antibodies, as well as inhibition of angiotensin-converting enzyme 2 (ACE-2) binding to multiple Delta (B.1.617.2) variant spike proteins.