2 vaccine doses better than 1 in preventing COVID-19 hospitalization, study says

New research out of the United States is driving home what public health officials and COVID-19 vaccine manufacturers have been repeating for months: two doses are better than one.

The U.S. Centres for Disease Control and Prevention (CDC) study found that a single dose of the Pfizer-BioNTech or Moderna vaccine is 64 per cent effective against hospitalizations in adults over 65 years of age. That number leaps to 94 per cent at least 14 days after a second dose of the same vaccines.

The small-scale study surveyed 417 older adults in 24 hospitals spread across 14 states.

Yet it provides more real-world evidence of what had already been proven in clinical trials for both the Pfizer and Moderna vaccines, which found very similar results to the CDC study.

“It proves what we’ve already been saying: one dose provides pretty impressive protection, but obviously not nearly as much as two doses,” said Isaac Bogoch, an infectious disease expert at the University of Toronto.

The study also drives home just how effective the vaccines are, Bogoch adds.

“Ninety-four per cent effectiveness is fantastic for a respiratory virus (vaccine),” he said. “So we clearly have to get two doses.

“All this tells me is even after one dose, we still have to be careful.”

Both Pfizer and Moderna unveiled their vaccines late last year with guidance that the second shot in their two-dose regimens should be taken at least three to four weeks after the first.

Canada’s National Advisory Committee on Immunization extended that gap by up to four months in order to ensure large-scale vaccinations amid limited supply — what Bogoch has called the “first dose fast” strategy.

According to federal data, over 24 per cent of the population had received at least one dose of the vaccine as of April 23. Yet only 2.37 per cent has gotten their second jab.

With Canadians now waiting months before getting fully immunized, Bogoch says it’s critical Canadians understand that one dose doesn’t make them invincible to the virus.

“We need very clear communication from senior public health officials — in all languages, to all age groups —– to inform people that even after the first dose, while your risk (of severe illness) is lower, it’s not low enough that you can give up these public health measures just yet,” he said.

1:10 Getting 1st COVID-19 vaccine dose ‘doesn’t negate your need to be responsible’: Ontario’s top doctor

Officials across the country have been reminding Canadians to keep adhering to public health measures after their first dose, but have largely framed it more as a responsibility to protect unvaccinated people.

“If (you’re) not with your household and you’re not using precautions, you still might be carrying it and you still might transmit it to someone who you thought was vaccinated and is not vaccinated,” Ontario’s chief medical officer of health Dr. David Williams told reporters Monday.

“It does not negate your need to be responsible.”

Earlier this month, Manitoba officials noted that 10 people had died within 14 days of receiving their first or second dose of the vaccine — all during the window of time when the body has not yet developed immunity.

Experts have previously told Global News that “vaccination doesn’t prove that you are immune.”

Bogoch says the new CDC data shows the importance of maintaining public health measures until “significant vaccine coverage” is achieved across the country.

Even then, the measures “can’t be rolled back too soon.”

“You still have significant rates of community transmission and only people with partial immunity following one dose, so the population is still susceptible,” he said. “They might be less susceptible, but they’re still susceptible.”

He’s also urging people to remember to book their second dose when they have the opportunity.

CDC data found that nearly eight per cent of Americans who have received their first dose — roughly five million people — have missed their second doses. Similar data is not yet available in Canada.

“Vaccines are truly the way out of this pandemic,” Bogoch said. “We need people fully protected before we can start getting anywhere close to normal.”