Even as federal officials say the pause in use of Johnson & Johnson's (J&J's) single-dose Covid-19 vaccine isn't likely to hamper America's vaccination campaign, some experts are concerned it may fuel an increase in vaccine hesitancy, which may put at risk the country's efforts to curb the epidemic.

Several states suspend J&J distribution plans

In a joint statement Tuesday, CDC and FDA recommended a pause in the use of J&J's single-dose Covid-19 vaccine after six people—out of about 6.8 million Americans who have received the vaccine so far— developed a rare and severe type of blood clot called cerebral venous sinus thrombosis (CVST). According to the statement, the agencies recommended the pause "out of an abundance of caution" as CDC and FDA scientists examine the potential link between the vaccine and CVST.

According to Roll Call, the pause will have an immediate effect on vaccination sites receiving vaccine doses directly from the federal government, including community vaccination sites, mobile vaccination units, retail pharmacies, and sites operated by the Federal Emergency Management Agency.

In addition, following the statement, more than two dozen states on Tuesday announced they would remove J&J's vaccine doses from their distribution plans for the time being, CNBC reports.

For example, Danny Avula, Virginia's vaccination coordinator, in a statement released Tuesday said the state "will cease" administering J&J's vaccine until CDC and FDA "complete" their investigation. Meanwhile, the Connecticut Department of Public Health recommended all Covid-19 vaccine providers stop using J&J's vaccine "for the time being," and the Massachusetts Department of Public Health notified the state's vaccine providers to pause administering the vaccine "effective immediately."

Other states took similar actions, including Colorado, Florida, Illinois, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Michigan, Minnesota, Missouri, Nebraska, New Hampshire, North Carolina, New York, Rhode Island, South Dakota, Texas, Utah, and West Virginia.

Similarly, Walgreens Boots Alliance and CVS Health announced they would immediately pause administering J&J's vaccine.

Federal officials say pause may last 'days to weeks'

However, during a White House briefing Tuesday, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and chief medical advisor for the White House's Covid-19 response, said the pause in use of J&J's vaccine will likely last "days to weeks, rather than weeks to months."

Separately, Janet Woodcock, FDA's acting commissioner, during a briefing Tuesday said she expects the pause will last only "a matter of days."

Moreover, Jeff Zients, the Biden administration's Covid-19 response coordinator, said the pause "will not have a significant impact on [the country's] vaccination plan," adding that "Johnson & Johnson vaccine makes up less than 5% of the recorded shots in arms in the United States to date."

According to Zients and other officials, the United States should have enough vaccine doses from Pfizer/BioNTech and Moderna to vaccine all American adults, Politico reports. And Pfizer CEO Albert Bourla in a tweet Tuesday said his company has ramped up production of its vaccine and "can deliver 10% more doses to the U.S. by the end of May than previously agreed," which means the company would deliver the federal government's entire order of 300 million doses two weeks ahead of schedule.

Several state officials also said they don't expect the pause will interfere with their vaccination campaigns. For example, Washington State Secretary of Health Umair Shah said J&J's vaccine represented "such a small proportion of the [state's] vaccines overall that … it should have minimum [impact]."

Meanwhile, Oklahoma State Department of Health's Deputy Commissioner Keith Reed said, "We have plenty of the Pfizer and Moderna vaccine on hand to ensure that every Oklahoman who wants a vaccine can get one."

In addition, officials from Louisiana, New York, Missouri, South Carolina, and other states said they don't anticipate any issues with their state-run mass vaccinations, and they intend to use the vaccines developed by Pfizer/BioNTech and Moderna to honor the appointments people had scheduled for the J&J vaccine, Roll Call reports.

Will the pause fuel vaccine hesitancy?

However, even as many experts and officials praised CDC and FDA for acting quickly to investigate potentially severe side effects, many also expressed concern the pause could fuel broader vaccine hesitancy at an inopportune moment when the country's vaccine campaign needs to outpace coronavirus variants.

Paul Simon, the chief science officer for the Los Angeles County Department of Public Health, said, "We are concerned about heightened reservations about the J&J vaccine, but in addition to that, those reservations could spill over into public concerns about other vaccines."

"I salute the CDC for erring on the side of caution to give everybody that sense of confidence," Connecticut Gov. Ned Lamont (D) said during a press conference. "A number of the governors thought, though, that the White House team was a little naive when they said that this is just going to be a pause, and then we restart our engines."

"This is going to scare a lot of people, and rightfully so," said Noel Brewer, professor of health behavior at the University of North Carolina at Chapel Hill. "We should all be concerned about the safety of medicines we receive. In this case, there's not a lot of reason for concern. The actual risk is vanishingly small."

According to the Times, vaccinators have already started receiving questions from concerned patients.

Ultimately, Rupali J. Limaye, who studies public health messaging at the Johns Hopkins Bloomberg School of Public Health, said the challenge will be getting people to understand the relative risk, noting that the potential risk of blood clotting in response to J&J's vaccine is much lower than the rate of blood clotting for cigarette smokers and women using hormonal contraception.

Maulik Joshi, the president and chief executive of Meritus Health, which administered 50,000 doses of all three vaccines without reports of any major side effects, said he uses a simple message to assuage patients' fears: "It's a great thing that they have paused it, and this is science at work" (Allassan/Fernandez, Axios, 4/13; Banco/Roubein, Politico, 4/13; Breuninger, CNBC, 4/13; Cohen/Kopp, Roll Call, 4/13; Christ, Modern Healthcare, 4/14; Bowden, The Hill, 4/13; Wingrove/LaVito, Bloomberg, 4/13; Stolberg/Hoffman, New York Times, 4/13; Baker, Axios, 4/14).