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

Hall VG, Ferreira V, Ierullo M, Ku T, Majchrzak-Kita B, Kulasingam V, Humar A, Kumar D. Delayed-interval BNT162b2 mRNA COVID-19 vaccination enhances humoral immunity and induces robust T cell responsesNat Immunol (2022). doi:

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

In this CITF-funded study led by Dr. Deepali Kumar of the University Health Network, Toronto, researchers followed healthcare workers (HCW) who received the Pfizer Comirnaty vaccine. One group received their second dose after the standard 3-to-6-week interval; the others waited 8 to 16 weeks between doses. While all HCWs developed immune responses post-vaccination, those with a longer interval between doses had a higher number of antibodies and a higher neutralizing capacity against the Alpha, Beta, and Delta variants of SARS-CoV-2. The results are published in Nature Immunology.

Key findings:

  • All participants developed immune responses following vaccination.
  • Antibodies against a specific portion of SARS-COV-2 – the receptor binding domain (RBD) – were significantly higher in the longer interval group compared to the standard interval group.
  • Neutralizing antibody levels against the Alpha, Beta and Delta variants were also significantly higher in the longer interval group compared to the standard interval.
  • T-cell levels (part of cellular immunity) were the same between groups.

A total of 93 HCW were included in this study. Of these, 39 (41.9%) received their second dose of the vaccine at the standard interval (3 to 6 weeks) and 54 (58.1%) received their second dose at the longer interval (8 to 16 weeks). Most participants were female (79.6%) and the median age for the cohort was 40.9 years.

This study provides evidence that a longer interval between vaccine doses produces stronger immune responses. This is of great importance to public health decision makers around the world who are planning vaccination strategies.