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

Asamoah-Boaheng M, Goldfarb D, Prusinkiewicz MA, Golding L, Karim ME, Barakauskas V, Wall N, Jassem AN, Marquez AC, MacDonald C, O’Brien SF, Lavoie P, Grunau B. Determining the Optimal SARS-CoV-2 mRNA Vaccine Dosing Interval for Maximum Immunogenicity. Cureus. 2023 Jan 31;15(1):e34465. doi:

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

A CITF-funded study, published in Cureus, examined the impact of different dosing intervals between the first two COVID-19 mRNA vaccines. Intervals longer than 38 days, compared to a short interval of less than 30 days, resulted in higher levels of SARS-CoV-2 anti-spike antibodies. The longest interval (74 days and greater) was associated with the highest SARS-CoV-2 spike IgG antibodies. Both the long interval (39-73 days) and the longest interval (74 days and greater) were associated with higher receptor-binding domain (RBD) IgG antibody concentrations. This study was led by Dr. Brian Grunau in collaboration with Drs. Pascal Lavoie and Agatha Jassem (all three from University of British Columbia), along with Dr. Sheila O’Brien (Canadian Blood Services).

Key findings:

  • Vaccine dosing intervals between the two initial mRNA COVID-19 vaccines beyond 38 days resulted in higher levels of SARS-CoV-2 anti-spike antibodies. Specifically, both the long (39-73 days) and longest (74 days and greater) intervals were associated with increased spike total antibody concentration at six months after the first vaccine dose compared to the short interval of 30 days or less.
  • Compared to the short interval, the longest interval was associated with higher SARS-CoV-2 spike IgG antibodies, while the long and longest intervals were associated with higher receptor-binding domain (RBD) IgG antibody concentrations.
  • There was a continuous rise in antibody levels with extended vaccine intervals, with no apparent plateau up to 130 days.
  • The longest vaccine interval, in comparison to < 30 days, was associated with higher levels of inhibition of the cell receptor angiotensin-converting enzyme 2 (ACE-2)SARS-CoV-2 spike protein binds to this cell receptor to initiate the first step of viral infection. , when assessed six months after the first COVID-19 vaccine.

The authors highlight that these findings have important implications for vaccine strategies and public health decision-making. Policymakers and clinicians using this body of literature, when making decisions about the benefits of longer dosing intervals, can balance the need for immediate immunity with the advantages of enhanced long-term immunogenicity. These considerations are also relevant for optimizing global vaccine distribution, allowing for delayed booster doses and improved coverage in under-served regions. These findings may also be relevant for future pandemics.

The study population consisted of 564 samples from the COVID-19 Occupational Risks, Seroprevalence, and Immunity among Paramedics in Canada (CORSIP) observational cohort study, which is a longitudinal study examining seroprevalence and workplace risks of SARS-CoV-2 exposure among paramedics (aged 19 and older) working in British Columbia, Alberta, Ontario, Saskatchewan, and Manitoba.

Samples collected for this analysis were drawn from adult paramedics in Canada who received two doses of either BNT162b2 or mRNA-1273 vaccines and provided blood samples six months after the first vaccine dose received between December 16, 2020, and September 13, 2021.