Ontario health officials have said that two doses of a COVID-19 vaccine offer better protection against the Delta variant of the virus.
Dr. Barbara Yaffe, associate chief medical officer of health, made the comments at a press conference on June 7.
“If you’re vaccinated, particularly if you’ve had two doses, you are very well protected against the Delta strain. Particularly with the mRNA vaccine,” Yaffe said.
“The more people are protected, the less the strain can spread. It doesn’t matter that it’s very transmissible, if we’re vaccinated and we use good infection prevention and control, we will be able to blunt its spread.”
Dr. Theresa Tam, the chief public health officer of Canada, has said that the Delta variant has “certain mutations” that may impact the effectiveness of vaccines.
It is also at least 50% more transmissible than the initial strain of COVID-19.
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According to a study on the effectiveness of the Pfizer vaccine against the Delta and Beta variants, those with only one dose are “likely to be less protected” against the mutations.
Data from the study, published in The Lancet, showed that after one shot, only 21% of people had a lowered neutralizing antibody response against the initial strain of COVID-19.
However, this number jumped to 68% for the Delta variant, and 75% for the Beta strain.
Neutralizing antibodies, or NAbs for short, are antibodies that defend cells from disease-causing organisms.
This data “raise the possibility” that the Delta variant presents a “dual challenge” of reduced vaccine efficacy similar to the Beta strain, and increased transmissibility beyond the Alpha.
The study’s authors caution that a single dose still affords “considerably more protection” than no vaccination at all. Two doses are needed, they write, to protect against the variant.
To date, Ontario has seen 536,607 COVID-19 cases and 8,869 deaths.