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COVID-19 survivors may only need one vaccine dose, study says

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A single dose of a COVID-19 mRNA vaccine could provide the same level of protection or higher in a person who has recovered from the virus than someone with no history of infection who has received both shots, a new study has found.

If widely accepted, experts say it could be a pivotal part of the race to achieve herd immunity.

“The reason why we get two doses of some of these vaccines is to prime our immune system and then boost our immune system after that priming,” said Dr. Zain Chagla, an infectious disease specialist at St. Joseph’s Hospital in Hamilton, Ont.

“If you think about it simplistically, getting natural COVID is the same as that first dose, that priming of the immune system, and then adding the vaccine gives you the boost on top.”

Read more: ‘Risky’ or ‘incredible’? Experts split on delaying 2nd vaccine dose to expand coverage

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The study, which was released Wednesday in the New England Journal of Medicine, provides a limited snapshot of antibody responses in 340 participants ranging from the ages of 22 and 70 years old. Researchers found the antibodies of participants who had already been diagnosed with COVID-19 were 10 to 15 times higher than people who hadn’t already contracted the virus after their first vaccination.

The median antibody titres — which is a measurement of how many antibodies an organism produces — in COVID-19 survivors increased by a factor of six after the first dose.

After the second dose, the study found that titres in patients with no history of the virus in their system increased by three, while former COVID-19 patients saw no antibody titre increase at all.

The study is one of several cropping up examining the effects of the vaccine on people who have previously been diagnosed with COVID-19.

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“We’re really looking at saving doses,” Chagla said.

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“Unlocking as many doses for people that are naive to COVID is a lot more important now, given that you actually do probably need both doses to get to that point.”

Currently, Canada has detected more than 900,000 cases of COVID-19 throughout the country, although health officials estimate the real number is three to five times higher due to initial limited testing availability and asymptomatic carriers who may not have known they needed to get tested.

Based on those numbers, Chagla said the federal government could save between three and five million doses of the vaccine if this system was integrated.

“Why not start doing things like antibody testing on the day you get your vaccine? And if your antibodies are positive, you’re done. You don’t have to come back… If they’re negative, then you get your whole series,” he said.

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The study comes as Canada works to extend the window between first and second vaccine dose intervals.

On March 3, the country’s National Advisory Committee on Immunization released updated guidance recommending provinces and territories wait up to four months between doses to compensate for vaccine shortages.

“Current evidence suggests high vaccine effectiveness against symptomatic disease and hospitalization for several weeks after the first dose, including among older populations,” the committee said.

Read more: Provinces, territories can wait 4 months to administer 2nd COVID-19 shot, NACI says

With a four-month interval in place, NACI added 80 per cent of the eligible population could be vaccinated with at least one dose by the end of June.

“Extending the dose interval to four months allows NACI to create opportunities for protection of the entire adult population within a short timeframe,” the committee said.

“This will not only achieve protection of the adult population, but will also contribute to health equity.”

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