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A Virginia woman who died after suffering from a rare blood clot is one of six cases federal authorities are examining to determine whether the illnesses are related to the Johnson & Johnson vaccine — an investigation that led them to recommend a nationwide pause on the one-dose regimen Tuesday.

Virginia Department of Health officials said they received word from the Centers for Disease Control and Prevention that the woman’s death was being examined by the agency as it investigates possible side effects of the Johnson & Johnson vaccine.

The Virginia woman, 45, died on March 18, according to the Vaccine Adverse Event Reporting System, the system the CDC uses to monitor symptoms after vaccinations. She received the vaccine on March 6 and began feeling ill six days later, according to the report. The woman, who was not identified, died after suffering from cerebral venous sinus thrombosis in conjunction with thrombocytopenia, or low blood platelets — the combination of conditions that federal officials are investigating.

The pause on Johnson & Johnson vaccinations caused government officials and pharmacies in D.C., Maryland and Virginia to scramble Tuesday to cancel coronavirus vaccination appointments and switch vaccines at clinics that had been poised to administer the Johnson & Johnson shot.

Officials said it was too soon to say if the pause would ultimately slow the region’s efforts to vaccinate all people over 16, who are eligible for appointments in D.C. and Maryland. In Northern Virginia, all adults in Loudoun County and Alexandria are eligible, and Fairfax, Prince William and Arlington counties must expand eligibility by April 18.

“What it will do is to slow down the progress through Phase 2. We won’t be able to have quite as many appointments available for first doses next week and beyond,” Danny Avula, Virginia’s vaccine coordinator said in a call with reporters Tuesday. About 72,000 Johnson & Johnson doses were expected to be distributed in 30 clinics in Virginia this week, which is about 15 percent of the total doses scheduled, he said.

The effect of the pause might be mitigated, at least in the short term, since Johnson & Johnson this week delivered fewer vaccine shipments to D.C., Maryland and Virginia — and nationally — than officials initially expected.

The drop-off was stark. D.C. received 1,300 Johnson & Johnson doses this week, compared with 10,800 last week. Maryland received 10,500 doses this week and 88,800 last week, while Virginia received 14,800 doses this week but 124,700 last week, according to the CDC’s tracker.

In D.C., about 16,000 residents have received the Johnson & Johnson vaccine through the city’s appointment system, Health Director LaQuandra Nesbitt said. Maryland vaccinated 173,500 people with the Johnson & Johnson vaccine, according to state data. About 184,000 Johnson & Johnson doses have been administered so far in Virginia, Avula said. More than 7.2 million people have received the Johnson & Johnson shot nationwide.

Virginia Gov. Ralph Northam (D) said he hoped the pause would represent a “small setback” in the overall vaccine distribution effort, but noted the plan to have college students vaccinated by the end of the school year could be delayed.

“Our goal is still to have all Virginians receive at least one dose by the end of May,” he said.

Northam spoke after touring a vaccination clinic at Grace E. Metz Middle School in Manassas, run by the city and Walgreens, which switched the Tuesday and Wednesday vaccination clinics from the Johnson & Johnson vaccine to Pfizer-BioNTech.

The clinics are intended to reach parts of Virginia with some of the highest per capita infection rates and Latino residents who may worry they will be asked for documentation or otherwise distrust the government.

While the first batch of doses thawed, Prince William County health district officials told people waiting in a long line about the change in vaccines, and took down their information to schedule a second dose. Officials planned to administer at least 1,700 doses over two days.

Janet Palomino, 69, who waited in line with her husband, Andres, on Tuesday said she would go through with being vaccinated with the Pfizer doses but had mixed feelings about the Johnson & Johnson pause. She knew friends and relatives who worried about the safety of the shot, but she felt the one-dose vaccine meant she might have been protected from the virus sooner.

“No vaccine is 100 percent,” she said. “The important thing is to get it as soon as you can.”

The Palominos were infected with the coronavirus late last year and Andres was sick for two months, she said.

“Horrible,” she said of the virus’s toll and a trying year, while her husband stood quietly beside her.

The District canceled 1,200 Johnson & Johnson vaccine appointments Tuesday, and Nesbitt said those patients should have received a link that afternoon offering them any unfilled appointment slots left over this week or first dibs on appointments for next week.

A larger number of Johnson & Johnson doses was delivered to the city’s federal agencies — the Defense and Veterans Affairs departments received just over 4,000 of the shots this week, Nesbitt said — and to nonprofits and pharmacies that receive their doses directly from the federal government, which also received about 4,000 doses total for the week.

Those clinics also canceled appointments, and not all had the option of offering alternate appointments using Moderna or Pfizer. Michael Kim, owner of Grubbs Pharmacy, said he would reschedule his patients as soon as possible but also advised them to look elsewhere.

Nesbitt encouraged residents to keep their trust in the other two vaccines.

“The pause shows that the system is working,” she said. “We remain confident in these vaccines.”

At an outdoor clinic hosted by the nonprofit Bread for the City on Seventh Street NW, several people who got vaccinated Tuesday said they were wary of the Johnson & Johnson option even before learning about the CDC’s decision.

Mohamed Dow, 58, who is unemployed, had wanted to get the Johnson & Johnson vaccine because he thought it would be more convenient to get one dose. Now he feels a sense of relief that he never did.

He had no concerns about the Moderna vaccine he got.

“It’s better to get it,” he said. “It’s worth the risk.”

Maryland officials have switched from Johnson & Johnson to other vaccine doses for appointments at their Hagerstown and Salisbury mass vaccination sites.

Maryland’s deputy health secretary, Jinlene Chan, said the Health Department is evaluating how long the state can continue administering about 69,000 ­doses per day if the Johnson & Johnson vaccine is not available.

In the meantime, she said, residents should “take the pause for what it is: and that is to assess the data and determine what the concerns are.”

The Johnson & Johnson vaccine has not been proven so far to cause the blood clots. Chan encouraged residents to consider the significant benefits of the state’s vaccination program with populations where there are high vaccination rates showing dramatically fewer coronavirus ­cases, hospitalizations and deaths.

“We want to balance the risk with the benefits, and we have seen a benefit since we started rolling out the vaccine,” she said.

The 960 people scheduled for Johnson & Johnson vaccinations at Montgomery County’s mass vaccination site in Germantown woke up to an email Tuesday morning informing them that they could receive the first dose of Pfizer or cancel their appointments.

Leaving the Germantown clinic, Kyle Warfield, 36, said he was relieved the jab was not painful and that the process had gone so smoothly, despite the vaccine shuffle.

“To make such a massive change in no time at all is really impressive,” he said.

Warfield, who said he hates needles, had considered canceling his appointment because of a deluge of seemingly conflicting information on the Internet but was driven by the desire to reunite with family members who he has not seen in person in more than a year.

“There is so much information out there — right or wrong you have no idea,” he said. “It’s a lot to take in.”

Public health experts praised the development of the one-shot Johnson & Johnson vaccine as key to protecting vulnerable individuals who may find it difficult to return for the second in Pfizer-BioNTech and Moderna’s two-dose regimens.

That includes people who are hospitalized, the homeless and groups who disproportionately suffer from underlying medical conditions that can make covid-19, the disease caused by the coronavirus, more severe and deadly.

Homer Hervey, 55, received the Pfizer shot in Germantown but said he would have been comfortable receiving the Johnson & Johnson vaccine given the rare occurrence of severe symptoms.

“The only thing that was a bummer was I was hoping it was a one-shot deal,” said Hervey, of Bethesda. “But I’m happy to be here and to get it done.”

Erin Cox, Paul Schwartzman and Rebecca Tan contributed to this report.