EVERETT — Following federal guidance, Washington health care providers are temporarily pausing Johnson & Johnson shots while experts educate hospital systems on how to treat a rare side effect that may be linked to the single-dose vaccine.

Of the nearly 7 million people nationwide who have received the Johnson & Johnson vaccine, officials have identified six cases of brain blood clots.

“This action is being taken out of extreme caution,” said state Secretary of Health Dr. Umair Shah during a news conference. “This rarity of a side effect, one in a million, while it is serious, it has to be reminded to people that this is rare.”

On Wednesday, a federal vaccine advisory group will review the blood clot cases. Johnson & Johnson shots could resume in a matter of days, Shah said.

The pause, he added, gives officials time to tell doctors to avoid prescribing Heparin, a blood thinner, to treat the side effect.

In many cases, the drug is used to prevent blood clots. But in this instance, it could cause severe damage, Shah said.

For those who got the vaccine more than a month ago, the risk of this complication is very low, the Department of Health said in a news release.

“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,” the agency said. “It also demonstrates how well the robust vaccine safety monitoring systems work, since this potential safety concern was identified quickly and vaccines were paused to allow for further investigation.”

Angel of the Winds Arena in Everett is Snohomish County’s only mass vaccination site that offers the single-shot vaccine. Some pharmacies and mobile clinics also offer the J&J vaccine.

All appointments at the arena have been cancelled. The Snohomish Health District will reach out to people to reschedule.

Comcast was set to host a Johnson & Johnson clinic Wednesday and Thursday at its office in south Everett, with help from QFC. People who signed up will now receive a Pfizer dose and be scheduled for a second appointment in three weeks.

Across Washington, Johnson & Johnson’s vaccine makes up about 6% of the state supply.

In Snohomish County, providers have administered about 24,000 Johnson & Johnson doses, health district officer Dr. Chris Spitters said.

Officials are worried that news of the one-in-a-million side effect will make people more hesitant to get vaccinated.

“I am anxious to see it resolved quickly,” Spitters said. “Hopefully we wrap this up in a few days and get back to work.”

The pause comes two days before the state expands vaccine eligibility to everyone 16 and older.

This week, 30,000 vaccine doses are coming to Snohomish County, Spitters said. About half are designated for second shots of either the Pfizer or Moderna vaccines, which, unlike the J&J shot, require two doses.

With more people getting in line and fewer doses to go around, securing a shot will be difficult, officials warn.

“Please don’t get discouraged,” Snohomish County Department of Emergency Management Director Jason Biermann said Tuesday. “I understand folks get frustrated because appointments arrive and flee very quickly.”

Joey Thompson: 425-339-3449; jthompson@heraldnet.com. Twitter: @byjoeythompson.