Our province has announced that anyone who received a first dose of the AstraZeneca vaccine can get a second dose of any mRNA vaccine. That means, if they meet provincial eligibility criteria for their second dose, they can get either Pfizer or Moderna.

Dr. Joss Reimer is head of our province's Vaccine Implementation Task Force. She says for weeks they have been waiting for the results of a UK study that was looking at second doses for people who received a first dose of AstraZeneca. According to Dr. Reimer, the results of the study were expected to be released by the end of May, but that has not happened. In fact, the estimated release date is now in late June.

"We had been waiting because the data release timing was ideal for us to have the most updated scientific information prior to when the first recipients of AstraZeneca reached their twelve week mark," explains Dr. Reimer. "But late June is far too late for us to wait for."

However, Dr. Reimer says results from a Spanish study have been released, showing that people who received a second dose of an mRNA vaccine after AstraZeneca had a good immune response.

"This is consistent with what we have seen in vaccines for other diseases as well," she says. "We've seen that changing products in between doses for almost every other vaccine still results in good effectiveness and ultimately that's what we're after."

As a result, all Indigenous people in Manitoba and individuals with specific health conditions are eligible to book their second dose, as long as they meet the minimum time interval between doses. If anyone in these groups received a first dose of AstraZeneca, the minimum time interval between doses is 28 days.

Even though 28 days or four weeks is the minimum window between first and second doses, the Spanish study recommends eight to 12 weeks.

"I know that if you got AstraZeneca, the not knowing has been difficult and stressful," she says. "What we're doing for the second dose doesn't change, that you choosing AstraZeneca as the first vaccine that was available to you, was and still is the right decision."