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, particularly when it's in short supply, there appears to be consensus thatpolicy makers should attempt to limit deathsandtarget the most vulnerable.

But some researcherssuggest that by the second stage, oncemore 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 eitherdemographic groups or even individuals who have more contacts," said ChrisBauch,a University of Waterlooprofessor of applied math who helped developa computermodel to determine the bestvaccine deployment.

That appears to be at odds withrecommendations put forwardby 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 livesduring the pandemic, such as essential workers and first responders,should be inoculated.

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

In thefirst few months of the rollout, officials estimate aboutthree million Canadians could be inoculated with the two-dose vaccine. Thevaccines will be distributed to jurisdictions on a per-capita basis, soeach provincewill receivevaccine dosesin numbersproportionateto its share of the population.

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Elderly andhealth 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 forwardby the committee.

For the first stage, thecommittee 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 70as supply becomes available.
• Health-care workers,including all those who work in clinicalsettings 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 vaccinateindividuals who are more likely tospread the virus orthose who aremost likely to die of COVID-19,it's important to consider what we know about avaccine's efficacy at curbing transmission.

Currently, there is not enough data to show thatPfizer-BioNTech's vaccine prevents transmission of the virus, she said. What's more, curbing transmissionmore widely wouldrequire 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," shesaid.

When it came to deciding what groups should get the vaccine first, the committee reviewed a lotof literatureto identify risk factors for complications and mortality. Theyalso 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 thehealth-care system and then to not have commercial disruption of the society," she said.

The committeealso 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, NACIrecommended 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, includingpolice, firefighters and those infood production.

Thoserecommendations, saidQuach-Thanh, were basedin parton what the committee definesas "reciprocity" that is,giving the vaccine to people who have alreadyrisked their lives during the pandemic, including health-care workers, first responders and other essential workers, suchas those who work ingrocery stores,where it is difficult if not impossible to socially distance.

"If you have to choose because you don't havethe number of vaccines that you require, I think you have to also look at the other elements," she said. "And the ethicshere 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, theUniversity of Waterloo math professor,said he agrees withNACI's first-stage strategy of targeting the vulnerable. Indeed, his own research foundif 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 thempotentially spreading the virusto others.

"At some point, more deaths can be prevented through indirect protection instead of direct protection," he recently wrote for The Conversation, whichpublishesarticles 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 whichevaluates vaccines in populations. Her research concluded that when there areonly enough vaccinedosesto 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 sixmillion dosesin 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 targetgroups who have frequent contact with other people, such asyounger adults and children.

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