Six women came down with a rare blood-clotting disorder within two weeks of receiving the Johnson & Johnson COVID vaccine, prompting federal authorities to recommend Tuesday that states pause in distributing the vaccine just as broad vaccine eligibility begins.

The Food and Drug Administration and the Centers for Disease Control say they are temporarily stopping the administration of the Johnson & Johnson vaccine this week while they investigate the blood clotting cases, and they're recommending that states do the same. As the New York Times reports, all six cases were women between the ages of 18 and 48, and one has died, with another hospitalized in critical condition in Nebraska.

The clots "occurred in veins that drain blood from the brain," and they occurred together with low platelet counts, as the Associated Press reports. And the clotting disorder appeared to be similar to the rare and unusual cases found in recipients of the AstraZeneca vaccine in Europe, a vaccine which still has not received U.S. approval.

The pause means that all federally operated mass-vaccination sites will stop giving out the Johnson & Johnson shots until further notice, but this comes after some 6.8 million doses have already been administered.

"We are recommending a pause in the use of this vaccine out of an abundance of caution,” said Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, and Dr. Anne Schuchat, principal deputy director of the CDC, in a joint statement. "Right now, these adverse events appear to be extremely rare."

The pause may further heighten fears among the vaccine-hesitant and further complicate the speed of the vaccine rollout nationwide. However, as the Times notes, shipments of the J&J vaccine have been far smaller than the 23 million combined doses per week coming from Pfizer and Moderna. Neither of those vaccines have shown any significant safety issues.

In New York City, where the city's mass vaccination program has depended heavily on the Johnson & Johnson shots, things may get even more complicated when it comes to convincing a hesitant public that the vaccine is still OK.

New York City Councilmember Mark D. Levine went on Twitter Tuesday morning to say, "NYC now has the biggest messaging challenge yet in vaccination. We have to do everything possible to avoid a collapse in confidence in vaccination overall."

The mass-vaccination site at New York's Javits Center had been giving out primarily J&J shots, and Levine later tweeted that those with J&J appointments would instead be given Pfizer shots at that site.

UCSF infectious disease specialist Dr. Peter Chin-Hong says that people shouldn't be too worried about this pause, and should go ahead and get the J&J vaccine if they want it. He also points out that this is a recommendation and not a mandatory pause.

"One in a million... not terrible odds compared to the odds of getting sick and dying of COVID," Chin-Hong said speaking to KRON4 about the blood clot risk.

The Moscone Center in San Francisco has only seemed to offer J&J appointments in the last two weeks, however the site has been stocked with the two other vaccines as well — and a dip in Johnson & Johnson supply was expected this week anyway. The Oakland Coliseum site just switched back from exclusively administering Johnson & Johnson shots when FEMA ended its management of the site on Sunday.

As ABC 7 reports, California was expecting a 33% drop in vaccine supply compared to last week due to a shortage of Johnson & Johnson shots.

Still, our state's numbers are looking better and better. As of Monday, 72% of the state's population over the age of 65 has been vaccinated with at least one shot, and 42% of the population ages 16 and up have received one shot or more.

Despite Latinx people representing 39% of the state's population, only 22.3% have received one vaccine shot.

On Thursday, San Francisco County begins allowing everyone age 16 and up to receive a vaccine, and this is already allowed in multiple Bay Area counties including Alameda and Contra Costa. Two drop-in clinics in San Francisco opened eligibility on Friday to all adult residents in eight zip codes where the city is prioritizing the vaccine rollout.

Update: San Francisco said it would pause administering the Johnson & Johnson vaccine, which the city says makes up a small fraction of doses already given out — and this week, there were 500 J&J shots allocated out of the 10,000 total vaccines the city received, as the Chronicle reports. No appointments are expected to be canceled. Acting SF Health officer Dr. Susan Phillip urged people to go ahead with their vaccines and to know the city would only be giving out Pfizer and Moderna shots for now — and of the 31,831 doses of the J&J vaccine administered to SF residents, no cases of blood clots have occurred to date.

The health department said in a statement, "As this adverse event is reported to be extremely rare with just over six reported cases nationwide, we do not believe there is cause for immediate alarm."

Top image: A pharmacist volunteer prepares doses of the Johnson and Johnson COVID-19 vaccine during a pop-up clinic at Western International High School on April 12, 2021 in Detroit, Michigan. The state of Michigan has seen an explosion of COVID-19 cases despite a massive effort to roll out vaccines. Pop-up clinics in various communities are one of the ways the state government is trying to get the surge under control. (Photo by Matthew Hatcher/Getty Images)