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Halting the AstraZeneca Vaccine Over Blood Clots Could Do More Damage Than Good

The evidence is still very patchy that the vaccine increases blood clot risk. But even if it does: So does the birth control pill.

A nurse administers the AstraZeneca Covid-19 vaccine to a patient.
Asanka Ratnayake/Getty Images

The AstraZeneca vaccine rollout was already chaotic. But overly jumpy governmental decisions may have made it even worse. Countries like Denmark, Norway, France, Germany, and Italy all temporarily halted AstraZeneca vaccinations in the past week amid reports of some people developing rare blood clots after getting the shot. The move followed false starts in the clinical trials (the vaccine may not match the efficacy those trials promised) and production and distribution of the shots falling well short of targets. Skepticism of the vaccine was high even before shots went into arms or early reports of potential side effects were reported.

And yet: The AstraZeneca vaccine works. Even if it may not work as well as anticipated against some variants—a recent study suggests it’s not effective against the South African variant—it is still at least 60 percent effective against others, meaning those who receive the vaccine are 60 percent less likely to get symptomatic Covid-19 than those who do not. It’s not clear how common the blood clots actually are, whereas the risk of catching and dying from Covid-19, which is surging once again across Europe, is significant. Halting vaccinations, even temporarily while the blood clot concern is investigated, could mean more lives are lost than saved—and it could damage already fragile trust in both the vaccine and government agencies.

As Covid-19 continues to rage across Europe and other parts of the world, the AstraZeneca situation reveals the deepest questions of the pandemic: How do you weigh the need to move quickly and save lives against the potential loss of trust these decisions may bring? How much information do you need before you act?

On Thursday, after an investigation of the AstraZeneca blood clot reports, the European Medicines Agency announced that the vaccine was both safe and effective. But even prior to that, the EMA had said that “the benefits of the AstraZeneca vaccine in preventing COVID-19, with its associated risk of hospitalisation and death, outweigh the risks of side effects.”

The World Health Organization has taken a similar tack, continuing to recommend vaccinations while monitoring for rare side effects. “It’s routine practice to investigate them, and it shows that the surveillance system works and that effective controls are in place,” Dr. Tedros Adhanom Ghebreyesus, director-general of the WHO, said during a press conference on Monday. “But the greatest threat that most countries face now is lack of access to Covid-19 vaccines.” (On Thursday, President Biden announced that the United States would send millions of AstraZeneca doses to Mexico and Canada.)

The decisions of multiple countries to conduct reviews based on reported side effects is normal and good. But halting vaccinations until the review has been conducted is an unusual step, usually taken if the side effects are more common or serious than previously thought.

Normally, between 300 and 650 of every 100,000 people develop blood clots over the course of a year. So far, 17 million people have received the AstraZeneca vaccine, and only 37 people have reported blood clots. That actually seems like a lower rate of clots than normal. And in the United Kingdom, where about 11 million of these vaccinations have taken place, no such side effects have been linked to the shot.

However, two patients in Austria and four patients in Norway have developed different blood clotting disorders, and three of the six patients died. In Germany, where 1.6 million people have been vaccinated, six women and one man between the ages of 20 and 50 developed cerebral venous thromboses, or blood clots in the brain, days after receiving the shot. Three of the patients died. In a population of 1.6 million people over two weeks or so, officials would expect to see one case of this type of clot; seven cases rang alarm bells and raised concerns that these illnesses were related to a bad batch of doses in Europe. “Today’s decision is a purely precautionary measure,” Jens Spahn, Germany’s health minister, said on Monday. Yet these precautions could work to undermine already shaky confidence in the vaccine.

In the meantime, Covid-19 cases in Germany have gone up 20 percent in the past week. “We’re in the midst of an emerging third wave, and things are just going to get worse from the Covid perspective,” Dr. Claire Standley, an assistant research professor at Georgetown University’s Center for Global Health Science and Security who is based in Germany, told me.

If all of the AstraZeneca Covid-19 vaccines came with an increased risk of blood clots, reports of blood clots in the U.K. would likely have been higher, Dr. Adam Finn, a professor of pediatrics at the University of Bristol, told me in an email. Halting vaccinations until officials figure out the potential relationship is a tricky decision to make, he said. “In the context of the current pandemic and urgency to protect high-risk individuals, decisions to delay—and which may create public doubts—should be made carefully.”

It’s possible that these unusual blood clots happened for an entirely different reason, which could explain why they occurred in some countries and not others. Even if these clots are linked to the vaccine, they still seem to be incredibly rare. And the risks of short- and long-term effects from Covid-19, including blood clots, are more significant, experts argue.

Blood clots can be a side effect of many medications, including birth control pills, whose blood clot risk likely far exceeds that of any Covid vaccine. That doesn’t mean governments should ban them. “We allow women to make that choice for themselves. We provide them information,” Standley said, in order for each individual to make their own decision. “So why aren’t we allowing individuals that same choice when it comes to the AstraZeneca vaccine?”

She worries that the German government, facing elections in six months, is being overly cautious in a way that could backfire. If the blood clot risk is debunked and then a different, and potentially more serious, correlation shows up in a month, “are people going to think that the government’s crying wolf? How is this going to work in terms of government trust?” Standley asked. Instead of halting life-saving vaccines, officials should say there is a potential risk but they will continue to gather data and, in the meantime, offer information on the side effects to look for, she said. “Germany has thousands of new Covid cases every day; we’re still facing hundreds of deaths every day; cases are increasing. I just find it very difficult at this point in time that the government is restricting the use of a tool that we know can help save lives.”

To some extent, this entire situation was to be expected. When a new medication is developed, a clinical trial can only show you so much. While massive clinical trials of 30,000 or 40,000 people can catch many side effects, they may not flag one-in-a-million events. Experts told me they would expect some very rare side effects to emerge as the vaccine reaches millions of people around the world. In the U.S., for instance, prophylaxis is a rare side effect to mRNA vaccines. As a result, in the current U.S. vaccine rollout, individuals who have had severe reactions to shots may choose a non-mRNA vaccine, while others wait in vaccination clinics to make sure they don’t have reactions. When new information about a medication emerges, as it invariably does, we adjust course based on evidence.

But people can have blind spots when it comes to evaluating risks, Dr. John Moore, professor of microbiology and immunology at Weill Cornell Medical College, told me recently when I asked him about safety concerns over the speed of the vaccines’ production. “Across society, people’s assessment of risk is often just way off the mark. There’s a very small risk of a vaccine side effect. There’s a very significant risk of getting and dying of Covid,” he said. “There’s nothing that is perfectly safe. Otherwise, you’d stay in bed all day, and then you’d probably die of bed sores. People have to be informed of as much information as available and then make their own choices.”

Results from the U.S. trials of the AstraZeneca vaccine, run in partnership with the U.S. National Institutes of Health, are expected any day now. The results could affect the vaccine’s future—will weaknesses from these trials cast further doubt, or will the evidence back the argument for continuing to use the AstraZeneca vaccine? The question is particularly fraught because the AstraZeneca vaccine, with its relatively easy storage and low price tag, has been seen as an ideal vaccine for developing countries.

In many ways, the AstraZeneca vaccine shows us how good we have it with others. Jabs from Pfizer-BioNTech, Moderna, and Johnson & Johnson were developed at lightning speed, with complicated trials and rollouts—and each cog in these massive machines turned as it should have. Of the millions of shots administered, not one person has died because of the vaccination.

Standley was recently reviewing her notes on the pandemic from last July, when questions abounded about when a vaccine would be available and how safe and effective it would be. “If we could go back to that point in July 2020 where we weren’t sure what was going to happen in terms of vaccines, and someone said, you will have a two-in-a-million chance of a severe adverse reaction—would that have been considered acceptable at the height of the pandemic when people were so scared of what was going on and the vaccine was a miracle?” She suspects most people would have jumped at the chance—and still would, as hospitalizations and deaths continue to mount.