2nd stage of COVID-19 vaccination should target those most likely to spread the virus, say some experts

When it comes to the first stage of administering the vaccine for COVID-19, there appears to be wide consensus that policy makers should target the most vulnerable. But some researchers suggest by the second stage, that strategy should change to trying to prevent the spread.

1st stage will focus on vulnerable, but once more vaccine is available, focus should be reducing transmission

A nurse prepares a shot of the Pfizer-BioNTech COVID-19 vaccine at Guy's Hospital in London on Dec. 8. The first shots of the vaccine will be available in Canada next week. (Frank Augstein/The Associated Press)

When it comes to the first stage of administering the vaccine for COVID-19, particularly when it's in short supply, there appears to be consensus that policy makers should attempt to limit deaths and target the most vulnerable.

But some researchers suggest that by the second stage, once more vaccine is available, that strategy should change to trying to prevent the spread.

"Once ... we've covered the vulnerable groups, they should seriously consider prioritizing according to contacts and vaccinating either demographic groups or even individuals who have more contacts," said Chris Bauch, a University of Waterloo professor of applied math who helped develop a computer model to determine the best vaccine deployment.

That appears to be at odds with recommendations put forward by Canada's National Advisory Committee on Immunization (NACI), which makes recommendations on the use of newly approved vaccines. It says that after the first stage of the vaccine rollout, those who have risked their lives during the pandemic, such as essential workers and first responders, should be inoculated.

(CBC News)

In the United Kingdom, people have begun receiving Pfizer-BioNTech's COVID-19 vaccine. On Wednesday, Health Canada announced it had also approved it. The first doses of vaccine arrived in Canada on Sunday night, with more to follow on Monday, meaning some Canadians should be receiving shots within days.

In the first few months of the rollout, officials estimate about three million Canadians could be inoculated with the two-dose vaccine. The vaccines will be distributed to jurisdictions on a per-capita basis, so each province will receive vaccine doses in numbers proportionate to its share of the population.

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Elderly and health care workers 1st in line

It's up to the provinces and territories to decide who will receive the vaccine first, but they seem to be following recommendations put forward by the committee.

For the first stage, the committee advises initial doses go to four groups:

  • Residents and staff of long-term care homes.
  • Adults 70 and older, beginning with people 80 and older, then decreasing by five-year increments to 70 as supply becomes available.
  • Health-care workers, including all those who work in clinical settings and personal support workers who come in direct contact with patients.
  • Adults in Indigenous communities, where infection can have disproportionate consequences.

Those guidelines line up with the Advisory Committee on Immunization Practices at the U.S. Centers for Disease Control and Prevention. That group recommended that if the vaccine is in limited supply, those who should receive it first are health care personnel, workers in essential and critical industries, people at high risk for severe COVID-19 illness because of underlying medical conditions and people 65 years and older.

Transmission data not clear

Caroline Quach-Thanh, the chair of NACI, said that when it comes to deciding whether to first vaccinate individuals who are more likely to spread the virus or those who are most likely to die of COVID-19, it's important to consider what we know about a vaccine's efficacy at curbing transmission.

Currently, there is not enough data to show that Pfizer-BioNTech's vaccine prevents transmission of the virus, she said. What's more, curbing transmission more widely would require 60 to 70 per cent of the population to be immunized, Quach-Thanh said.

"I think that given the disparity in vaccines and the lack of knowledge about decreasing transmission, you have to go for individual-level protection, which is protecting those that would suffer the most complications and/or get this virus," she said.

A woman is given a Pfizer-BioNTech Covid-19 vaccine at Cardiff and Vale Therapy Centre on Dec. 8 in Cardiff, Wales. (Matthew Horwood/Getty Images)

When it came to deciding what groups should get the vaccine first, the committee reviewed a lot of literature to identify risk factors for complications and mortality. They also conducted a survey of the public and different stakeholders, and the majority said the priority should be to "protect the most vulnerable first and then the health-care system and then to not have commercial disruption of the society," she said.

The committee also looked at whether any specific populations were at a particularly higher risk or disadvantage because of systemic factors, which led to the inclusion of remote Indigenous communities in the first stage.

Stage 2 recommendations

For Stage 2 of the vaccination rollout, NACI recommended that recipients include:

  • Health-care workers not included in the initial rollout.
  • Residents and staff of all other congregate settings (e.g., living quarters for migrant workers, correctional facilities, homeless shelters).
  • Essential workers, including police, firefighters and those in food production.

Those recommendations, said Quach-Thanh, were based in part on what the committee defines as "reciprocity" — that is, giving the vaccine to people who have already risked their lives during the pandemic, including health-care workers, first responders and other essential workers, such as those who work in grocery stores, where it is difficult if not impossible to socially distance.

(CBC News)

"If you have to choose because you don't have the number of vaccines that you require, I think you have to also look at the other elements," she said. "And the ethics here is a huge part of this decision making. Reciprocity was one value that was important for us.

"People who have been putting their life on the line to protect us and our society need to be prioritized." 

Strategy should switch

Bauch, the University of Waterloo math professor, said he agrees with NACI's first-stage strategy of targeting the vulnerable. Indeed, his own research found if vaccination starts sufficiently early in 2021, vaccinating individuals 60 years of age and older will prevent the most deaths.

By the second stage, a switch in strategy that would focus on vaccinating people who have many contacts would be prudent to reduce the risk of them potentially spreading the virus to others.

"At some point, more deaths can be prevented through indirect protection instead of direct protection," he recently wrote for The Conversation, which publishes articles from the academic and research community.

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Laura Matrajt is an applied mathematician at the Fred Hutchinson Cancer Research Center in Seattle which evaluates vaccines in populations. Her research concluded that when there are only enough vaccine doses to cover less than 50 per cent of the population, as is the case in the first phase of Canada's vaccination plan, it's best to vaccinate those who are at higher risk. 

The government has said that Canada, with a population of 38 million, will have access to six million doses in the first three months of inoculation, which requires people to get two doses of vaccine.

With larger quantities of vaccine, Matrajt said, it makes sense to target groups who have frequent contact with other people, such as younger adults and children.

"If you have a lot of vaccine and concentrate on giving it to those transmitting the virus, you're indirectly protecting those at higher risk by actually containing the outbreak."


Mark Gollom

Senior Reporter

Mark Gollom is a Toronto-based reporter with CBC News. He covers Canadian and U.S. politics and current affairs.

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