ongoing

This real-world study is addressing the marked and unexpected reduction in the supply of the mRNA vaccines to Canada, as of January 2021, which has led to a policy change of delaying the second dose of the Pfizer vaccine to healthcare workers (HCW) up to 35 to 42 days. There is little evidence to support this policy, which could be harmful if immunity diminishes to low levels, leaving HCWs at risk of infection before the delayed second dose.

Furthermore, there is no data to inform how dosing schedules may impact on the secondary immune responses and long term immunity. However, this policy represents a potential natural experiment and an opportunity to study the impact of dosing schedule on vaccine immunogenicity as it relates to short and long term immunity. Since the sequence and timing interval of dosing to HCWs are largely randomly generated; the variation in time interval between the first and second vaccine doses is unbiased and unaffected by any factors other than by chance.

We therefore propose an opportunistic study in which we will study and address the following questions:

  • What are the cellular immune responses and humoral responses to the first dose of mRNA vaccine up to 42 days and following the second dose up to 12 months.
  • How does the dosing schedule impact on the secondary immune responses and long term immunity. The study will be conducted in HCWs, a high risk group across 3 tertiary hospitals in Hamilton, Ontario, Canada.

Primary Objectives:

1. Examine the NAb levels and cellular immune responses at days 35-42 compared to day 21 following the first dose of mRNA vaccine.

2. Characterize the profile of NAb and cellular immune responses following the first dose of vaccine up to 42 days and following the second dose up to 12 months

3. Contrast the profiles of NAb and cellular immune responses between 21-day dosing interval (correct cohort) versus delayed 35-42 day dosing (delayed cohort) interval of vaccine.

Secondary Objective:

To explore the threshold levels for NAbs and cellular immunity associated with significant reduction in infection risk of symptomatic SARS-CoV2 infection.

The secondary objective will be exploratory as the study is not powered to examine this objective. The findings will help to guide the planning of a larger study to address this particularly question.

Collaborators include Mark Loeb, Dawn Bowdish, Matthew Miller, Ishac Nazy, Zain Chagla, Jonathan Bramson, and Judah Denburg.

Study Type

Observational

Study Design

Prospective cohort study

NO. of Countries

1

NO. of Sites

1

NO. of Participants

128

Study Period

2021

Sponsor

PHRI

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