Canadian health authorities have announced that Covid-19 vaccines will be mixed and matched in order to ensure a quicker roll-out of the national vaccination programme.
The announcement from the Public Health Agency of Canada (PHAC) was based on an updated guidance from the National Advisory Committee on Immunization (NACI), which recommended that a first dose of the AstraZeneca vaccine, including the Covishield version manufactured by the Serum Institute of India, could be followed by a second dose of either the Pfizer-BioNTech or Moderna vaccine.
It also recommended that the doses for the two mRNA vaccines can be switched if necessary.
In a statement that accompanied an official release, NACI chair Caroline Quach-Thanh said, “We know that the question of which vaccine will be used for second doses, in particular for individuals who had received the AstraZeneca/Covishield vaccine as their first dose, has been a question for many people in these last few months.
“NACI has seen additional data on the safety of using mixed Covid-19 vaccine schedules and NACI has also seen some data on the immune response following this mixed schedule.
“Based on that evidence, but also on the risk of the rare but serious adverse event called VITT that is associated with the viral vector vaccines, we are recommending that someone who received a first dose of the AstraZeneca/Covishield vaccine may receive an mRNA vaccine for their second dose.”
Quach-Thanh added, “The committee strongly recommends that if one mRNA vaccine was used for the first dose, the other mRNA vaccine can be used as the second dose if needed. Second doses are important for more robust and long-term protection. These NACI recommendations on mixed schedules will provide flexibility for provinces and territories in the move towards second doses.”
Theresa Tam, Canada’s chief public health officer, said, “This rapid response on the interchangeability of authorised Covid-19 vaccines will guide decision-making by provinces and territories as we continue to roll-out Canada’s Covid-19 vaccination campaign.”
The NACI release stated that current evidence suggested that mixing the viral vector first dose with an mRNA second had a “good safety profile at shorter (four-week) and longer (8 to 12-week) intervals” and that there is “evidence that providing an mRNA vaccine after AstraZeneca vaccine will boost the immune response, which is what we expect from a second dose”.
NACI’s earlier position had been that the second dose administered had to be from the same inoculation applied for the first.
However, in light of emerging evidence of interchangeability, primarily from research in Spain and the UK, Canadian health authorities updated their stand on Tuesday.
NACI underscored that this was not an unusual step, as it noted that was “not a new concept” and similar vaccines from different manufacturers have been used to complete a vaccine series for influenza, Hepatitis A and others.
In fact, on Monday, the province of Manitoba had already announced that those who received the AstraZeneca vaccine as their first dose could get another for their second.
Canada has so far given emergency authorisation to four vaccines, Pfizer-BioNTech, Moderna, Astra Zeneca/Covishield, and Johnson & Johnson, with the last one requiring a single dose.
Among the issues that health authorities could resolve with the new recommendation is that of lack of availability of the AstraZeneca vaccine.
