An abundance of caution and good science are the right way to build trust in vaccines

On Tuesday the US Food and Drug Administration and Centers for Disease Control and Prevention recommended a pause on the use of the Johnson & Johnson vaccine in the United States. In six cases, women between the ages of 18 and 48 experienced a “rare and severe” blood clot after receiving the vaccine. This is out of over 1 million women in the 20-50 age group who have received doses of J&J.

Meanwhile, an estimated 1 in 5 people hospitalized for Covid-19 develops blood clots. All in all, the risk of blood clots from the J&J vaccine is extremely low when compared to the risk of blood clots in these other contexts.

It’s normal for people to worry, but we’re really bad at weighing risks. We tend to overemphasize the risk of action, like getting vaccinated, and underemphasize the risk of inaction, like not wearing a mask in a pandemic or not wearing your seat belt in the car. We worry about the risks of something new, like vaccines, but play down the risks we’re used to, like getting in a car accident while driving to work.

The blood clots observed among these six women who received the J&J vaccine are similar to those seen among patients in Europe after receiving the AstraZeneca Covid-19 vaccine. Both vaccines are based on modified adenoviruses, as are the Russian Sputnik V vaccine and the Chinese CanSinoBIO vaccine.

Adenoviruses are just some of the viruses associated with the common cold, but the viruses in these vaccines have been altered so they can’t replicate and infect the vaccine recipient. They’ve been modified to deliver the recipe for the SARS-CoV-2 spike protein to human cells. When our immune system sees the spike protein, it learns to recognize SARS-CoV-2 and fight it off.

Many of us in the medical and public health community now wonder whether the altered adenovirus could be setting off an abnormal immune response that in very rare cases causes low platelet counts and blood clots, what some are now calling “vaccine-induced immune thrombotic thrombocytopenia.”

The Vaccine Adverse Event Reporting System (VAERS) is co-sponsored by the CDC and FDA; they should be commended for their careful surveillance for side-effects related to the Covid-19 vaccines.

These blood clots are rare. There was one case in Johnson & Johnson’s Phase 3 trial, but at the time it was determined to be unrelated to the vaccine and the case is being reexamined now in light of the other six cases.

Some have criticized the FDA and CDC for recommending a pause on the use of the J&J vaccine in the US. To be clear: the FDA didn’t revoke its emergency use authorization for the vaccine. It didn’t take the vaccine off the market. And health care providers are still free to administer the vaccine after discussing the potential risks and benefits with their patients. The CDC and FDA are acting out of a reasonable and appropriate abundance of caution.

Firstly, the FDA and CDC had to inform the public of these possible side-effects so that patients, doctors and other health care providers know what to be on the lookout for and how to treat complications. It’s common and normal for people to experience headache, fatigue, fevers, chills and muscle pain in the first couple of days after vaccination. But if someone has a headache, abdominal pain, leg pain, or shortness of breath one or two weeks after vaccination, that’s cause for concern, and patients should seek medical attention to rule out blood clots.

When we as health care providers care for a patient with a blood clot, the first drug we usually reach for is heparin. But heparin is the wrong treatment here. In this setting, heparin could make things worse and could even be deadly. This is because heparin can cause a similar syndrome, but the good news is that we have many other drugs to choose from.

Secondly, it’s essential that the FDA and CDC prove themselves to be trustworthy. Worries about vaccine safety and efficacy and a lack of trust in the health system and government drive low confidence in vaccines. It is essential that the FDA and CDC demonstrate to the public that they are taking seriously any risk, even the most minuscule, and continuously evaluating vaccine safety and efficacy honestly, rigorously, and transparently. Dismissing any risk could fuel greater mistrust.

On Wednesday the CDC’s Advisory Committee on Immunization Practices held a special meeting to review data of blood clot cases. They did not vote on changing any recommendations for Johnson & Johnson’s coronavirus vaccine — including no vote on extending a pause in administering the vaccine.

Either way, the use of the J&J vaccine may fizzle out in this country. Some saw the vaccine as being an inferior product, with lower efficacy against infection and milder disease in clinical trials. But it’s important to note that the Johnson & Johnson vaccine was studied in South Africa and Latin America when the B.1.351 and P.1 variants were already widespread. Natural infection is less protective against both these variants, and the immune responses elicited by vaccination are relatively less powerful against them. Neither the Pfizer nor Moderna vaccines were subjected to the same stress test in clinical trials, but the mainstream media headlines often didn’t clearly communicate this nuance.

In the near term, the US supply of the Johnson & Johnson vaccine is likely to be limited due to manufacturing problems at the Emergent Biosolutions plant. But we are fortunate in this country to have multiple highly effective Covid-19 vaccines in our arsenal and in ample supply. More than 180 million doses of the Pfizer and Moderna vaccines have been administered in this country to date, according to CDC data, and we have not seen blood clots associated with either of those vaccines. The Pfizer and Moderna vaccines are based on a different technology. We will have enough supply of both of these vaccines to vaccinate all adults in this country on the Biden administration’s schedule.

What worries me is what this will mean for the global Covid-19 vaccine supply. We were counting on the AstraZeneca, J&J, and other adenovirus vector vaccines — which are cheap and don’t have strict cold storage requirements — to vaccinate the rest of the world. Last month, in an unprecedented collaboration between competing pharmaceutical companies, Merck announced that it would help Johnson & Johnson scale up production of its vaccine. This vaccine supply won’t come in time to vaccinate Americans, but it is essential to the global Covid-19 vaccine effort. But the safety of the J&J vaccine must be re-evaluated by the FDA and CDC before we send it around the world. Anti-vaxxers could breed mistrust and thwart our best efforts to stop Covid-19’s deadly spread.