Iowa Gov. Kim Reynolds called the pause a "surprising setback" for the state, "at a time when our vaccine efforts are showing much progress, and because states weren't informed in advance of the announcement, we were left to develop contingency plans in the moment for vaccine clinics scheduled yesterday and throughout the week."
"Putting even one vaccine on hold is disappointing," she added. "But ensuring a safe vaccination process, one that everyone can be confident in, will continue to be a top priority."
Other officials in the US said the interruption could have a major impact on college students, who were key targets for getting the single-dose vaccine before leaving school at the end of the spring semester.
Pause Is Important for Vaccine Confidence, Expert Says
But the move to recommend a pause is important for vaccine confidence, experts said.
"When you look at what our biggest obstacles are in the coming months, it is really around vaccine demand, or hesitancy or confidence," epidemiologist Dr. Celine Gounder told the United States Congress Joint Economic Committee on Wednesday.
"And one of the biggest drivers, especially in those who are most... resistant to getting vaccinated, it really comes down to either a lack of trust in health systems or a lack of trust in the government.
"So it is absolutely essential that the CDC and the FDA behave in a way that is transparent, honest, aboveboard, where they show they're doing their due diligence because that is really what's going to predict, in the longer term, whether people feel comfortable getting vaccinated," Gounder added.
Others however worry the pause may exacerbate Covid-19 vaccine hesitancy.
"I think it has a chilling effect," Dr. Paul Offit, director of the Vaccine Education Center at the Children's Hospital of Philadelphia, told CNN. "I think people may wrongly think, 'Well if it's true with this J&J vaccine maybe it's true with all vaccines.'"
The other two Covid-19 vaccines approved for the US -- Pfizer and Moderna -- are not implicated in the pause, officials have said.
Michigan Leaders Beg Residents to Get Vaccinated
In some parts of the country, officials are pleading with Americans to get vaccinated with the available vaccines to prevent another possible surge in Covid-19 cases.
In Michigan, a state already in the middle of another surge, Gov. Gretchen Whitmer and Detroit Mayor Mike Duggan emphasized the need for continuing vaccinations on Wednesday and predicted their troubling Covid-19 metrics will continue to rise.
Michigan cities currently account for nine of the 10 worst Covid-19 outbreaks in the country's metropolitan areas, according to the latest COVID-19 Community Profile Report published by the Department of Health and Human Services and the White House Covid-19 Team.
Over seven days, the Detroit metro area reported 581 Covid-19 cases per 100,000 residents -- more than 25,000 total cases -- the report shows, with some metro areas in Michigan reporting even higher per capita rates.
"The rate of infections in Detroit continues to climb and we know exactly why it continues to climb. And we are the only ones who can stop it," Duggan said Wednesday, urging residents to follow safety measures but also to encourage friends and loved ones to get vaccinated.
But it's not just Michigan.
Leading US officials have recently reported Covid-19 case and hospitalization increases -- predominantly in younger groups who have not yet gotten vaccinated -- fueled by dangerous variants circulating in the country.
"The virus still has hold on us — infecting people and putting them in harm's way — and we need to remain vigilant," CDC Director Dr. Rochelle Walensky said during a White House briefing last week. "We need to continue to accelerate our vaccination efforts and to take the individual responsibility to get vaccinated when we can."