The decision by two key federal regulatory agencies to recommend a pause in using the Johnson & Johnson COVID-19 vaccine got everybodys attention on Tuesday, especially since the progress had been so encouraging lately.

The impetus for the recommendation was six reports of medical incidents among the more than 6 million people who have gotten the Johnson & Johnson vaccine. In a joint statement, the two agencies, the Food and Drug Administration and the Centers for Disease Control and Prevention , said they were acting out of an abundance of caution in order to see whether these incidents were side effects of the vaccine and, if so, what that means for future use of the one-dose shot.

Johnson & Johnsons vaccine is one of three now available in the U.S. under emergency authorization orders. The other two are from Moderna and Pfizer-BioNTech.

All three vaccines induce human cells to produce the now-familiar COVID-19 protein spikes so that the bodys immune system learns to recognize the virus. But the Johnson & Johnson vaccine operates in a slightly different way than Modernas or Pfizers, neither of which have generated reports of such incidents.

Biden administration officials said Tuesday that the pause will not meaningfully affect vaccine distribution in the U.S. noting, among other things, that the Johnson & Johnson vaccine accounts for less than 5% of the shots that have gone into arms.

The U.S. is already averaging more than 3 million vaccinations a day, and there are already small pockets of the country where supply is reaching or outstripping demand, with more likely to follow soon.

Still, officials were hoping the J&J vaccine would boost the supply and provide a version that was easier to administer, because it requires just one dose rather than the two spaced-apart vaccinations that both Moderna and Pfizer require.

So what exactly did the FDA and CDC say today? Was that the right decision?What does it mean for the Johnson & Johnson vaccine, and the vaccination campaign more generally, going forward?

Joshua Sharfstein has thought a lot about these issues. He served as principal deputy FDA commissioner during the Obama administration. Before that term, he was health commissioner for the city of Baltimore. Afterward, he served as secretary of health for Maryland. Now he is a public health professor at Johns Hopkins University. (Hes also a friend Ive known for many years.)

HuffPost asked for his take on these questions. Here is a lightly edited version of our conversation, which took place over email.

Cohn: First thing: Can you translate for the public what the FDA and CDC actually have said and what it means?

Sharfstein: FDA and CDC are reporting that six people developed an unusual type of blood clots within two weeks of vaccination with the Johnson & Johnson vaccine. All six are women, between the ages of 18 and 48. One died, and a second is in intensive care. These reports are serious, but they are also very rare. More than 6 million people have been vaccinated with this vaccine so far.

The concern, for FDA and CDC and, of course, the rest of us, is that the vaccine may be the cause of this disorder that its not just a coincidence. To investigate and respond to this potential risk, the agencies have asked for a pause in the use of the Johnson & Johnson vaccine.

We should hear more soon, including at an advisory committee meeting scheduled for tomorrow, about what this means for the vaccination program. Todays announcement reflects that the national vaccine program is working to identify and assess even remote risks quickly.

Cohn: A pause. So how long are we likely taking here?

Sharfstein: I would anticipate well know more in days to several weeks.

Cohn: People want to know if these reports means the vaccine is unsafe. Can you put this into context for us, relative to other vaccines or drugs?

Sharfstein: When thinking about the safety of a drug or vaccine, I consider three questions.

First, how do the risks compare with the benefits? In this case, the benefits are impressive. Studies have shown that the Johnson & Johnson vaccine is quite effective at preventing illness from COVID-19. The vaccine appears to be even more effective at preventing serious illness and death.

FDA and CDC scientists are working now, first, to assess the likelihood that this unusual clotting problem is actually related to vaccination. And then, if they find it is likely to be related, they will have to weigh the very considerable benefits of avoiding COVID-19 against the potential harms of this unusual clotting problem for different groups of people. With this complication so rare, my expectation is that for all groups, they will find that the benefits far exceed the risks. The chance of a problem appears to be less, for example, than the risk of a severe allergic reaction to any of the COVID vaccines.