Q&A: Rationale for delayed second dose

Q: Please review the evidence that supports lengthening the second COVID-19 dose to four months.

A: The National Advisory Committee on Immunization (NACI) have recommended that the interval between first and second dose be lengthened to four months (see here for more information). This decision was in part, based on scientific and real world data, and also was felt to be an ethical decision. By lengthening the interval, it frees up more first doses for the broader population, to more quickly reduce transmission of COVID-19 in the community.


Dr. Danuta Skowronski presented the evidence of very good protection by a single dose.


The NEJM article shows strong evidence of protection for six months after natural infection. The antibody levels produced by vaccination are not lower, so there is every expectation that they will not diminish while waiting for the booster dose.  The evidence shows that a single dose provides very good protection.  Not only in healthy adults, but also in residents of long-term care (LTC) homes. A single dose dramatically reduced outbreaks in LTC.


Medical Staff Q&A were generated during the March 10, 2021 Medical staff forum.


Miss the March 10th Forum?  The AV recording of this and previous forums, as well as the full transcripts and a running list of Q&A are available on the intranet site and Slack.

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