Preliminary Ontario data shows lasting COVID-19 vaccine efficacy

OTTAWA -

Just days after new studies showed a possible waning in the effectiveness of the COVID-19 vaccine, new preliminary data from Ontario offers a beacon of hope. 

"This is very reassuring, not just because what we’re seeing overall is reassuring, but this is local data and it’s something that applies directly to us here in the province of Ontario," said Dr. Sumon Chakrabarti, an infectious disease physician in Mississauga. 

Earlier this month data published in the Lancet medical journal suggested the effectiveness of the Pfizer vaccine dropped significantly six months after the second dose, but new data from Ontario seems to counter that assumption. 

"There certainly is waning, it’s got to be acknowledged, we can’t sweep this under the rug, but it’s probably being overstated and overestimated in those studies," said infectious diseases specialist Dr. Isaac Bogoch. 

"It’s nothing that can be brushed aside, we have to acknowledge it, but we also have to acknowledge that other metrics like hospitalizations and deaths have very high effectiveness," he added. 

The new ICES preliminary Ontario data, which has yet to be peer-reviewed, shows that even eight months after the second dose Ontarians with two mRNA shots still showed a vaccine efficacy of 81 per cent against symptomatic illness and 96 per cent against severe illness, hospitalization and death. 

"It’s wonderful to have local data and especially high quality local data especially because you have smart policy that is reflective of the ground truth and the local situation here in Ontario and other parts of Canada," Dr. Bogoch said. 

New ICES preliminary data shows that eight months after the second dose Ontarian’s with two mRNA shots still showed a vaccine efficacy of 81 per cent against symptomatic illness. (Source: ICES Ontario)

Among the findings were two points of concern, including a high-degree of uncertainty in the amount of waning seen by those who received two doses of the AstraZeneca vaccine. 

"I think we have to take everything with a grain of salt, but if we sort of look in the crystal ball as to who would benefit from a third dose I think it’s fair to say that people who received two doses of AstraZeneca would probably benefit from a third dose, especially an mRNA vaccine," Dr. Bogoch said. 

The data also showed what could be a decline in efficacy among older adults in long-term care settings who received the Pfizer vaccine. 

"Our own Ontario data is showing that even in elderly people, (efficacy) is fairly well preserved except in one group which is the elderly in long-term care facilities who had Pfizer. We are seeing there is some decline in the amount of protection against severe disease," Dr. Chakrabarti said. 

Medical experts agree the data will be helpful in determining if booster shots are necessary, who qualifies, and when. 

"It does look like it’s going to be possibly helpful in individuals who have profound immune suppression; for example transplant, cancer, chemotherapy, individuals who are elderly and in long-term care facilities and possibly community dwelling people who are over the age of 65," Dr. Chakrabarti said. 

For most of the general population, doctors say the efficacy means a third dose likely isn’t something to focus on right now. 

"At the end of the day this vaccine is very likely a three-dose vaccine for most individuals; the question is who needs a third dose now, the answer is probably not that many people," Dr. Bogoch added.  

Ottawa residents say they’re reassured by the new data. 

"Medical science is that nothing is 100 per cent and I would way rather take my chances with 80 per cent," said Madeleine Humeny. 

"I think it’s great that the vaccine lasts that long and I hope it will last as long as possible," Kacper Fleszer added. 

With the push to get vaccines into younger arms, and Pfizer readying to send its data to Health Canada, medical experts say more studies focusing on the safety of the COVID-19 vaccines for children are critical. 

"I know everybody is really anxious to get the vaccination for kids going but I think it’s important for us to take a step back and ask the questions that would we would for any other medical intervention," Dr. Chakrabarti said.