Federal officials say they expect the recommended pause of the Johnson & Johnson COVID-19 vaccine to last only a few days and said it should not impact the United States’ vaccination goals.

The Food and Drug Administration and the Centers for Disease Control and Prevention announced early Tuesday morning that the agencies recommended a pause in Johnson & Johnson COVID-19 vaccinations while the agencies reviewed safety data.

Six female patients who received the vaccine reported blood clots six to 13 days after vaccination. Each of the women was between ages 18 and 48. So far, 6.8 million Americans have received the Johnson & Johnson vaccine, so the chances of experiencing a clot were about 1 in 1.1 million.

The FDA’s Center for Biologics Evaluation and Research Director Peter Marks told reporters on a call the pause is necessary to educate providers about the type of blood clot caused by the Johnson & Johnson vaccine, called a cerebral venous sinus thrombosis. Standard blood clot treatment does not work for this type of clot, and if the standard course of treatment is followed, it could cause further harm or even be fatal.

The only hypothesis health officials mentioned as the cause is that the adenovirus vaccine may create an extreme immune reaction in some people that causes platelet clots. Marks said there is no known link to birth control.

The Advisory Committee on Immunization Practices is set to meet Wednesday to review these cases and discuss the potential significance.

CDC Principal Deputy Director Anne Schuchat told reporters anyone who was vaccinated with this one-shot vaccine a month ago or more should not worry. But anyone who received the Johnson & Johnson coronavirus vaccine in the past few weeks should watch for symptoms including severe headaches, leg pain or abdominal pain that differs from typical post-vaccination symptoms.

Acting FDA Commissioner Janet Woodcock said these reactions are extremely rare and should not deter Americans from getting vaccinated for COVID-19. The pause is due to regular safety monitoring, she said.

“The message to patients who haven’t been vaccinated is to continue to get vaccines that may still be available to them,” Woodcock said.

Small effect on overall vaccine supply

White House COVID-19 Response Coordinator Jeff Zients told reporters the delay would not have a significant impact on the U.S. vaccination plan. The one-shot vaccines from Johnson & Johnson make up less than 5 percent of recorded shots in arms to date.

The U.S. has secured enough doses of the COVID-19 vaccines from two other vaccines by Moderna and Pfizer to continue vaccinating 3 million people per day, Zients said. States and the federal government plan to work quickly to get anyone scheduled for a Johnson & Johnson vaccine rescheduled for a two-dose shot by Moderna or Pfizer.

The pause will immediately impact the places that receive vaccines directly from the federal government: retail pharmacies, community vaccination clinics, mobile vaccinations units and sites run by the Federal Emergency Management Agency.

The move could shutter some mass vaccination sites. FEMA said it is working with states to find other vaccines.

“FEMA is committed to helping the President’s goal to ensure everyone who wants to be vaccinated can be. In alignment with the Centers for Disease Control and Prevention and Food and Drug Administration’s recommendation to pause the use of the Johnson & Johnson vaccine, effective immediately FEMA will stop administering this vaccine at our pilot Community Vaccination Clinics, as well as via our Mobile Vaccine Units,” said acting Administrator Bob Fenton in an emailed statement. “We are working with our state partners to determine the path forward and find alternative vaccine options for these sites.”

Georgia, North Carolina and Colorado reportedly shut down vaccination sites before the announcement because of adverse events experienced by people receiving the Johnson & Johnson vaccine.

States’ reactions

Some states that convened their own experts early in the pandemic to review vaccine approvals asked those panels Tuesday to review the new safety information.

California “will convene the Western States Scientific Safety Review Workgroup to review the information provided by the federal government,” state epidemiologist Erica Pan said in a statement.

Many states reported that the Johnson & Johnson vaccine comprised just 4 to 6 percent of total vaccines supplied to the state so far, and were expecting only a trickle of doses over the next month or more amid manufacturing issues that delayed millions of doses.

“It was such a small proportion of the vaccines overall that we had already gotten into the state and were going to get into the state for the next few weeks, it should have minimum disruption from that standpoint,” Washington State Secretary of Health Umair Shah said. “Down the road, if for whatever reason, you have supply chain constraints… if it’s not just a short-term issue but a long-term issue, then that can impact all of us.”

Shah emphasized he believed the pause would be temporary.

Still, the pause could have a bigger impact on reaching the most at-risk populations, since many states sought to leverage the single-dose shot to reach hard-to-reach communities.

In Florida, four mass vaccination sites and 14 mobile clinics supported by the federal government to reach the state’s most vulnerable populations will will only administer second doses of the Pfizer and Moderna vaccines, according to Samantha Bequer, press secretary for the Florida Division of Emergency Management.

Kentucky Gov. Andy Beshear, a Democrat, said the pause won’t close mass vaccination sites, but will slow vaccinations in prisons, delay pop-up sites for hard-to-reach communities and prevent vaccinations for people experiencing homelessness, some of the most vulnerable people in the state.

Other states said the pause would not make much of an impact.

“We have plenty of the Pfizer and Moderna vaccine on hand to ensure that every Oklahoman who wants a vaccine can get one,” the state health department’s Deputy Commissioner Keith Reed said in a statement.

Many states — including New York, Louisiana, South Carolina and Missouri — reported there would not be issues with state-run mass vaccination sites and that they would honor appointments with one of the two other vaccines authorized by the FDA.

Tom McCarthy, the executive director of Rhode Island’s COVID-19 response, said his state will not see much disruption. Rhode Island had seen a sharp decrease in Johnson & Johnson doses recently, so the state is already relying more heavily on Modena and Pfizer. So far, the state has only doled out 31,000 doses of Johnson & Johnson vaccine.

About 300 Rhode Islanders will have their COVID-19 vaccines rescheduled, McCarthy said. People who were scheduled to get vaccinated at a mass vaccination site will not have their appointments rescheduled, and will receive a Pfizer or Moderna dose.

Many mass vaccination sites in Alabama will continue to offer the Pfizer vaccine, State Public Health Officer Scott Harris told reporters Tuesday. More than 2 million vaccine doses have been administered in Alabama thus far and about 71,00 of those were Johnson & Johnson vaccines.

Still, the uneven impact from state to state ratchets up pressure on the White House to consider distributing the vaccine according to need rather than according to population.

“I want to call upon the federal government to help us because we’re hearing of reports from around the country of places that are not asking for more vaccine and are not using the vaccine that they’ve gotten,” New York City Mayor Bill de Blasio told reporters. “Let’s do the smart thing, especially in light of this Johnson & Johnson challenge…. Send them to New York City, for God sakes.”