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Why We're Terrible At Weighing The Risks Of The J&J Vaccine

Isis Gardner, left, receives a dose of the Pfizer COVID-19 vaccine at the Banning Recreation Center in Wilmington, Calif. The site switched from its original plan to use the Johnson and Johnson COVID-19 to the Pfizer vaccine. (Marcio Jose Sanchez/AP)
Isis Gardner, left, receives a dose of the Pfizer COVID-19 vaccine at the Banning Recreation Center in Wilmington, Calif. The site switched from its original plan to use the Johnson and Johnson COVID-19 to the Pfizer vaccine. (Marcio Jose Sanchez/AP)

After six women who received the Johnson and Johnson vaccine got rare blood clots, U.S. health regulators decide to pause the vaccine's rollout. Last week, after further deliberation, they reinstated the vaccine, with required warnings.

The adverse events are serious — this is, after all, a clot in one of the main veins that drains blood from the brain — but many experts and thought leaders were quick to point out the rarity of the event.

Others argued that the pause would harm the public’s trust in the COVID-19 vaccines in general. And still others felt like the pause should have only applied to the risk group most affected, namely women under the age of 50.

What was not widely discussed, however, were the health losses from the vaccinations that were not given. The J&J pause, like every health policy decision that we make, trades off risks and benefits. Human beings are notoriously bad at judging such tradeoffs, be they citizens, physicians or policymakers.

The challenges are far greater when dealing with exceedingly rare but fearsome risks --  like being eaten by a shark or suffering a deadly brain clot after a vaccine. In a seminal paper co-authored by one of us (Richard Zeckhauser), we demonstrated that when risk is in the air, fear clouds the cognitive processes. In particular, humans tend to neglect the probabilities of fearsome events.

The J&J pause, like every health policy decision that we make, trades off risks and benefits.

In the context of the J&J vaccine, one must consider the probability of getting COVID-19 against the probability of having an adverse event occur from the J&J COVID-19 vaccine. Although many popular media accounts pointed out that the risks from COVID-19 were far higher than those from taking the J&J vaccine, none made any clear attempts to quantify those risks.

It matters whether they are twice as high, 10 times as high, or even more.

The neglect of probabilities will often lead to serious errors in avoiding extremely low probability risks — like avoiding swimming at beaches (because of sharks), or avoiding a life-saving vaccine (because of brain clots, known as cerebral venous sinus thromboses). The losses entailed can be modest (losing the fun of swimming in the ocean) or serious, indeed life-threatening harm (being at a much higher risk of getting COVID-19 and its many complications).

Fearsome risks are often exacerbated by the media coverage surrounding these events as well. Examples of this have included the coverage of shark bites; plane crashes; and terrorist attacks — all exceptionally scary, but also exceptionally rare. Fear-generation supports revenue-generation through increased viewership of television channels and increased clicks to news stories. But, in the process, this type of coverage inadvertently contributes to a warped perception of how the public thinks about their risks and benefits. In short, click-bait media impairs public health. A pandemic makes us doubly vulnerable to misguided thought processes and the disastrous outcomes that follow.

This particular vaccine was hoped to provide benefits in protecting harder-to-reach communities and individuals who would take one shot rather than two.

Fear-stirring coverage also contributes toward policy measures that don’t always make sense relative to the risk of the event happening again. For instance, in 2001, Florida banned shark-viewing excursions as a result of a well-publicized shark bite. Politicians were criticized for pursuing actions that appeared to be in the public’s interest, but were largely fruitless (the example being the Florida shark-viewing ban).

To this end, the J&J's blanket pause across all demographics was regarded as controversial, even among health experts. This particular vaccine was hoped to provide benefits in protecting harder-to-reach communities and individuals who would take one shot rather than two. The highlight of an adverse event, and the knowledge that the authorities would pause its use, may inadvertently magnify overall vaccine hesitancy. Already, polls are showing that fewer than 1 in 4 unvaccinated Americans would get the J&J vaccine since the pause, and that far more believe the mRNA vaccines made by Moderna and Pfizer are safer.

To counter probability neglect, the media must stress the safety of the vaccines. They must highlight the immense benefits in terms of protecting individuals and reducing onward transmission to others. Headlines play a key role: A study from Columbia University researchers showed that almost 60% of content that is shared is done so without readers ever having opened the actual article. While most headlines around the J&J vaccine clotting events have focused on the clots, we have not seen nearly as many articles covering how safe the vaccines have been. For perspective, nearly 7 million people had gotten the J&J shot when six clots were reported. (Seventeen total cases have been now reported, including one man.)

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Moreover, physicians and public health experts should proactively discuss the safety and importance of the vaccines with their patients. They should emphasize the extremely impressive safety profiles, and the vastly greater expected harms to those who remain unvaccinated from the virus itself. Those expected harms are high for two reasons: the levels of circulating virus in the United States are still notable (we registered over 58,000 new cases on April 25), and consequences are significant, including an increasing number of young patients being hospitalized, as well as newer data suggesting that long term symptoms are more common than previously thought.

Finally, physicians should remind their patients that virtually everything done in medicine, whether procedure or medication, entails a risk. Appropriate treatments provide benefits that significantly outweigh those risks, and vaccines are key examples. Nonetheless, a younger woman, who could just as easily get an mRNA vaccine — which offers greater vaccine efficacy and avoids the risk of a blood clot — should likely accept the minor discomfort of a second jab and visit.

Probability neglect is a cognitive bias, and, like all such biases, is only partly subject to personal control. Rare but fear-inducing events — like deadly brain clots — will continue to influence the risks that we take, and those we avoid.

Little is lost if we skip the swim on a beach where shark risks are negligible. But skipping medical treatments or preventions that offer great benefits for minimal risks is always a costly error. Once we recognize the presence of this bias, careful evaluation, with help from the media and health experts, can help us avoid such costly errors. Much illness can be averted, and many lives can be saved.

Abraar Karan is a global health physician at the Brigham and Women’s Hospital and Harvard Medical School. Ingrid Katz is the Associate Faculty Director of the Harvard Global Health Institute and an Associate Professor of Medicine at the Brigham and Women’s Hospital and Harvard Medical School. Richard Zeckhauser is the Frank P. Ramsey Professor of Political Economy at the Harvard Kennedy School.

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