First AstraZeneca, and now Johnson & Johnson? Both are virus-vector vaccines designed to attack the COVID-19 virus, and now both have been suspended by Western nations over issues of rare but severe blood-clotting. The CDC and the FDA issued an “immediate pause” request this morning after six such cases came to light.

That’s six cases out of more than six million doses, and no one has yet demonstrated causality, as CNN’s expert points out:

The CDC and FDA recommend a pause for Johnson & Johnson's Covid-19 vaccine over "six reported US cases of a rare and severe type of blood clot." pic.twitter.com/sh7bw9N5ny

— CNN (@CNN) April 13, 2021

Six cases out of more than six million doses seems unlikely to have any real causality, but the CDC and the FDA aren’t taking any chances. These vaccines operate under an emergency-use authorization that bypassed some of the clinical-trial requirements of full authorization, don’t forget. The two agencies have monitored the rollout data very carefully to measure both safety and efficacy. It’s a bit like a broader FDA trial, in fact, and these kind of adverse reactions could cause manufacturers to temporarily suspend trials until the questions of causality could be answered.

That appears to be the purpose of the “pause,” which is not a revocation of the EUA. In fact, the FDA and CDC are requesting a voluntary pause, not ordering it, although thanks to liability issues the “request” probably will have the same effect:

“[The] CDC will convene a meeting of the Advisory Committee on Immunization Practices (ACIP) on Wednesday to further review these cases and assess their potential significance,” read a joint CDC and FDA statement that was issued on Tuesday morning. “[The] FDA will review that analysis as it also investigates these cases. Until that process is complete, we are recommending a pause in the use of this vaccine out of an abundance of caution. This is important, in part, to ensure that the health care provider community is aware of the potential for these adverse events and can plan for proper recognition and management due to the unique treatment required with this type of blood clot.” …

“In these cases, a type of blood clot called cerebral venous sinus thrombosis (CVST) was seen in combination with low levels of blood platelets (thrombocytopenia),” the statement read. “Treatment of this specific type of blood clot is different from the treatment that might typically be administered. Usually, an anticoagulant drug called heparin is used to treat blood clots. In this setting, administration of heparin may be dangerous, and alternative treatments need to be given.”

The FDA and CDC said that these cases are extremely rare but that an abundance of caution was required.

“COVID-19 vaccine safety is a top priority for the federal government, and we take all reports of health problems following COVID-19 vaccination very seriously,” the statement continued. “People who have received the J&J vaccine who develop severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination should contact their health care provider. Health care providers are asked to report adverse events to the Vaccine Adverse Event Reporting System.”

I’ve had the Johnson & Johnson vaccine and had no major issues with post-inoculation side effects. (I did have a strange arthritic-like effect in my inoculation arm a week later, but it went away within hours. I reported it to J&J, but it wasn’t bad and it hasn’t come back since.) According to this data, that’s true of 99.99991% of all J&J recipients. That doesn’t mean that a certain small subset of the population won’t have a specific and serious issue, but it also doesn’t mean there’s causality here either. This might just be coincidental to the vaccine.

For now, though, J&J will have to get taken off the front lines of the COVID-19 fight. We are expecting massive supplies of Pfizer and Moderna to arrive, but with all 50 states now making the vaccinations available to all adults, the demand will outstrip supply, at least for a while. That’s a shame, what with J&J’s easy storage and single-shot regime, and even once restored, this news might have people shying away from J&J’s vaccine when it still can help beat back COVID-19.

Update: Lots of debate already over whether the FDA and CDC have essentially killed the J&J vaccine. Nate Silver, Ben Shapiro, and MMFA’s Matthew Gertz think they have:

It's also a high-stakes test for the FDA, and they failed it, because of course lots of people are going to take away the latter message. https://t.co/dVlBxi2tYA

— Nate Silver (@NateSilver538) April 13, 2021

This is, in a nutshell, absolutely insane. You don't pause a vaccine rollout because there were 6 blood clotting cases in 7 million doses unless you are batshit loony.

— Ben Shapiro (@benshapiro) April 13, 2021

The medical establishment thinks not:

Dr @ashishkjha on @GMA on J&J:

"I think the FDA is getting it right…I believe the J&J vaccine is exceedingly safe. These are very rare events. But we don't know if they're linked to the vaccine and we don't know if there are other cases we've missed. So it's the right thing."

— Karen Travers (@karentravers) April 13, 2021

They might both be correct. The FDA and CDC might have done the right thing in the clinical sense and created an anti-vaccine backlash. It’s understandable that they might want to drill down and determine what demographic factors might create the problem before proceeding, but at this rate it would impact around 300 American even if giving J&J to the whole country. It might have been better to address it in parallel.