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In this Monday, March 15, 2021 file photo a vial of AstraZeneca vaccine is pictured in a pharmacy in Boulogne Billancourt, outside Paris. Questions remained Wednesday about the future of the Oxford-AstraZeneca vaccine in Canada, as Manitoba limited use of the shot and Ontario announced it planned to save an incoming shipment to use as second doses.  THE CANADIAN PRESS/AP/Christophe Ena, FileChristophe Ena/The Associated Press

Blake Shaffer is an assistant professor of economics at the University of Calgary. Stephen Gordon is professeur titulaire at Université Laval. Andrew Leach is an associate professor at the Alberta School of Business. Christine Neill is an associate professor of economics at Wilfrid Laurier University. Tammy Schirle is a professor of economics at Wilfrid Laurier University. Trevor Tombe is an associate professor of economics at the University of Calgary. Five of the six authors received the AstraZeneca vaccine as their first dose.

Economics has a term for when the private actions of an individual confer costs or benefits on other people. We call it an externality.

Economists often focus on “negative externalities,” which are associated with bad things, such as pollution or littering. If I do those things and only care about what affects me, I won’t take into account how my actions impose costs on others. The result: We get too much of these bad things. This is why climate change is such a challenge to tackle.

But there are also positive externalities, and the COVID-19 pandemic has shone a spotlight on a classic example: vaccines. When you get your shot, you receive the private benefit of being better protected against the virus, while also conferring benefits on others; by being less susceptible to infection, you’re one less link in the transmission chain of the virus, making infection in others less likely. Vaccination also reduces the likelihood that an infection leads to hospitalization, reducing strain on our public health system.

These public benefits are a massive reason why we vaccinate: to protect ourselves, yes, but also to protect others.

This is important to remember in the wake of analysis from the National Advisory Committee on Immunizations (NACI) and other public-health experts on the risks and rewards of getting vaccines from the pharma company AstraZeneca (AZ), as compared with waiting for mRNA vaccines from firms such as Pfizer or Moderna. The AZ vaccines are effective against the novel coronavirus, but they have been associated with very rare blood clots, distinct from run-of-the-mill ones because of how they are formed and their higher degree of lethality, which does decline when people know of the risks and how to respond.

The expert analysis has been meticulous and evidence-based, and it has shifted views on administering AZ vaccines; Ontario and Nova Scotia will pause their use in first doses. When making their recommendations, health experts are comparing your very small likelihood of developing a potentially fatal blood clot against the benefit of lowered chances of dying (or having a stint in the ICU) from COVID-19 while waiting for a different vaccine.

The benefit of getting vaccinated with AZ has changed over the past few weeks. While the risk of blood clots remains very low – even if slightly higher than early estimates – Canada is now receiving millions of mRNA vaccines every week, meaning wait times to receive an alternative vaccine have shrunk. As a result, it may well be the case that the decision to no longer use AZ for first doses in certain jurisdictions is now the right medical decision (and as economists, we are unqualified and unwilling to debate that). If so, governments should get efficacious AZ doses to places without the luxury of choice.

But to get to that determination, we shouldn’t only be comparing private risks with private rewards for individual vaccine takers. We must not ignore the transmission-chain and public-health benefits provided by getting shots into arms as soon as possible. Analysis focused solely on private risks and private rewards, while useful for individual decision-making, ignores the important public-health benefit of vaccination – or, for economists like us, the positive externality – which is to protect others, not just ourselves.

Many will reasonably ask: “Why should I take any personal risk just to protect others?” This is fair, and individuals should know their private risk-reward tradeoff before making decisions. But they should also know they are conveying benefits to others in taking the first vaccine available, and public-health officials should be loudly sharing that information. If people choose to consider the benefit that accrues to others when taking the vaccine, they protect you in doing so. If we all take this view, we all protect one another; if only private benefits are considered, the outcome is worse for all.

Those who stepped up to get vaccinated with AZ when called upon should take comfort in two things. First, you made the right choice for you. Case counts were high, and the vaccine’s protection mattered. Second, you helped to protect others and improved our public health; indeed, the flush of mRNA vaccines now is in part a result of Canadians who took AZ, moving others up in the queue. Every Canadian that opted to take AZ reduced the chances that other people got sick and helped get us more quickly to a point where we can travel, visit relatives, and reopen schools and businesses.

So thank you for doing that. Or, to use our jargon in a heartfelt way: Your positive externality should not be ignored.

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