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

Almeida ND, Schiller I, Ke D, Sakr E, Plesa M, Vanamala S, Moneger AL, Bazan M, Lucchesi C, Wozniak N, Fritz JH, Piccirillo CA, Pelchat M, Arnold C, Galipeau Y, McCluskie PS, Langlois MA, Dasgupta K, Mazer BD. The effect of dose-interval on antibody response to mRNA COVID-19 vaccines: a prospective cohort study. Front Immunol. 2024 February 15. doi:

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

A CITF-supported study, published in Frontiers in Immunology, found that delaying the second dose of an mRNA COVID-19 vaccine beyond approximately three months produced a more robust antibody response, despite this being a longer timeframe than was recommended by the vaccine manufacturers. This study was led by Dr. Marc-André Langlois (University of Ottawa), Dr. Bruce D. Mazer, Nisha D. Almeida, and Dr. Ciriaco A. Piccirillo (all from McGill University).

As primary COVID-19 vaccine schedules in Canada were different, in part due to supply chain issues, from the manufacturer recommended timelines that were based on clinical trial findings, researchers investigated the impact of delaying the second dose. Between January and March 2021, 328 participants from the McGill University Health Centre were recruited. Each provided serum or dried blood samples (DBS) at 28 days, three months, and six months after the second dose and 28 days after the third dose. Anti-spike, anti-RBD, and anti-nucleocapsid antibodies were assessed by ELISA. Associations between antibody levels and long (>89 days) versus short (<89 days) intervals between doses were reviewed.

Key findings:

  • Anti-S IgG was 31% higher and anti-RBD IgG was 37% higher in the long versus short interval participants across all time points.
  • Overall, anti-S and anti-RBD antibody levels increased at the 28-day mark and decreased significantly over the following six months.
  • Overall, anti-N antibodies slowly increased over time as SARS-CoV-2 transmission continued.

The authors argue this study confirms that mRNA vaccines were highly effective at inducing strong antibody responses among healthcare personnel and other essential workers and that longer intervals between doses produced a more robust antibody response. These reassuring findings underscore the rationale for adopting a longer dose-interval strategy to maximize the impact of available vaccines in the face of logistical and supply challenges in low-resource and other settings.