Health committee  Thank you for the question. NACI has been monitoring global vaccine effectiveness against a number of variants of concern. We have seen recent evidence from the United Kingdom looking at the delta variant or B1.617.2. That variant does seem to respond very well to two doses of either Pfizer or AstraZeneca vaccine.

Health committee  I'll start with this. Last week, NACI recommended that either the AstraZeneca/Covishield COVID-19 vaccine or an mRNA vaccine may be offered for the subsequent dose in a series started with the AstraZeneca/Covishield COVID-19 vaccine and that the previous dose should be counted and the series need not be restarted.

Health committee  That is an excellent point. I would say that with many data elements in this pandemic and the vaccine responses, that does continue to shift. Yes, on the risk of VITT following AstraZeneca vaccine, we have seen that change over time. It does continue to change. That informed consent process would ideally include a discussion about what is known and also the fact that it has been changing over time.

Health committee  NACI published new advice, as of last week, on the topic of mixing vaccine schedules. NACI has now recommended that either AstraZeneca COVID-19 vaccine or an mRNA COVID-19 vaccine product may be offered for the subsequent dose in a vaccine series started with AstraZeneca. Either may be offered.

Health committee  I would only add that NACI is also considering the same evidence. They are generally supportive of what Dr. Tam just said. Thank you.

Health committee  It's impossible to provide an exact date because the committee's deliberations are contingent on scientific evidence coming out of the mixed-schedule studies in the U.K. Therefore, depending on the progress of that research, the committee will be timing its advice very shortly after that.

Health committee  Effectiveness has been monitored in United Kingdom and also here in Canada. There are not currently published estimates looking at a 16-week or four-month effectiveness interval.

Health committee  Yes, I can attempt that. NACI has advised us that, based on what we know about the immune system, intervals that are longer can provide the immune system more time to generate a robust immune response. We have seen in some of the clinical trials, such as those for AstraZeneca, that a longer interval resulted in more protection and a better immune response.

Health committee  That is on the forward work plan for NACI. The committee is currently reviewing evidence on interchangeability across vaccine platforms. As Dr. Tam mentioned, we expect some of that evidence to become available later in the month or into early June. There has already been some news released from a Spanish study looking at the same.

Health committee  When we've looked at the national numbers, it's around the first week of June that individuals would start being available for their second dose, according to a 12-week or a three-month interval for AstraZeneca vaccine. I'll also note that NACI has advised us that up to 16 weeks could be considered for an interval.