The Johnson & Johnson vaccine needs an honest risk assessment

The Johnson & Johnson vaccine needs an honest risk assessment
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In recent weeks, a few people protected with the Oxford-AstraZeneca COVID-19 vaccine have had blood clots and now this has been picked up with the Johnson & Johnson vaccine too. The Food and Drug Administration and the Centers for Disease Control and Prevention paused the rollout of the Johnson & Johnson vaccine, as it needed more time to consider whether to allow its use again.

This comes at a tricky time for the USA, where although the Johnson & Johnson vaccine had only just been rolled out, states had designated it as a keystone in their plan to deal with COVID-19. As a one-shot vaccine that can be stored at regular vaccine clinic refrigerator temperatures, it has an enormous advantage over the two-shot Moderna and Pfizer vaccines that require super-cold specialized refrigeration for storage.

There is a worry that the news of the pause and the previously reported troubles with the AstraZeneca vaccine has caused people to question all vaccines. The concern is that people will be less willing to be vaccinated. We can think of this as a negative halo effect. The traditionally positive halo effect is a type of cognitive bias in which our impression of a person influences how we feel and think about their character. Marketers take advantage of the halo effect to sell to us. For example, when a celebrity spokesperson endorses a product, our positive thoughts of that celebrity can spread to our perceptions of the product itself. A negative halo effect is also an error in reasoning based on one trait you know of another person or thing. One negative aspect about a particular vaccine may drive us to have a negative evaluation about the whole category of vaccines.


But this negative halo effect isn’t the only driver of lowered vaccine take-up to be concerned about. The paradox we are likely to face in coming months is that the success of vaccines in preventing the serious effects of COVID-19 and most likely reducing transmission too — and the resulting falling numbers of deaths and cases — will contribute to people’s ambivalence about taking up their offer of vaccination.

“If numbers are going down, there is no need for me to take a vaccine.”

But it’s likely that we may see a rise in demand again as cases inevitably rise once again as new variants emerge and people become lax about adhering to public health measures that have arguably contributed more to falling case numbers than vaccines.

It’s only right that there should be continued transparency about vaccine trials and reports of real-world usage to guide further rollout and use of the vaccine across the world. However, context, as always, is critical here; but often it is not described well in public health campaigns or media reports. As well as the “pause” and the risks being expressed of taking the vaccine in these rare blood clots being reported, it’s important to tie these numbers to real-world, concrete examples of comparable activities so that people can anchor their decisions more effectively. Our brains are not usually so good at interpreting likelihoods unless we can relate them to everyday activities that have meaning in our lives.

Based on current U.S. reports, six women have developed blood clots in the brain after taking the Johnson & Johnson vaccine: approximately 7 million Americans received this one-shot vaccine. That’s over one-in-a-million in terms of risk. This needs to be balanced against its effectiveness against COVID-19 hospitalizations and death. But what else in our everyday lives carry comparable or greater risks than taking the Johnson & Johnson vaccine?


The risk of blood clots after taking the AstraZeneca vaccine is roughly equivalent to dying by driving a car in the U.K. for 250 miles. Every day, just getting out of bed is associated with a greater risk of dying than the risk of blood clots through taking the Johnson & Johnson vaccine. We make a trade-off daily between the risks associated with what we do and our enjoyment of life, even if we don’t think about these risks or perceive them accurately.

Here’s another example. A one-in-million likelihood is about the same as tossing a coin 20 times and having it land tails every time. You don’t need a good grasp of probability to understand how unlikely this is and it’s immediately more graspable than a one-in-a-million shot.

The challenge is to be clear about the risks in taking any COVID-19 vaccine in transparent and open ways, but also compare these risks with everyday risky activities that we don’t even think about. Vaccination was never going to be a simple task. It’s frankly astonishing that we have come so far, so quickly. But achieving herd immunity through mass vaccination will continue to be a tricky balancing act with reports of side effects, public opinion and emerging virus variants. All three are likely to remain unpredictable, and can transform rapidly.

Strategic vaccine campaign managers would do well to continue to be transparent about the relatively low risk that vaccination may present, while continuing to emphasize the risk that COVID-19 poses and how taking a vaccine can help protect not only individuals, but vulnerable family and community members too. The happy by-product is that we can engage in everyday life more freely. And that is a massive benefit to all.

Dr. Sarb Johal is a clinical psychologist and author of "Steady: A Guide to Better Mental Health Through and Beyond the Coronavirus Pandemic." He helped to shape New Zealand’s COVID-19 communications campaign.