Biden declared Tuesday that even with a temporary loss of J&J ’s one-shot vaccine, there is a huge supply of Pfizer and Moderna vaccines, enough that “is basically 100% unquestionable, for every single, solitary American.”

Perhaps more concerning than any worry about supply, however, is the potential blow to public confidence in all of the vaccines, as polls suggest potentially tens of millions of Americans are hesitant to get the shots that public health experts say are necessary for the nation to emerge from the pandemic.

The pause actually should have the opposite effect, boosting confidence that the government is putting safety first, Biden and top health officials said at a White House briefing. The advisory by the Food and Drug Administration and the Centers for Disease Control and Prevention — citing a need to investigate reports of rare but potentially dangerous blood clots — was “testimony to how seriously we take safety,” said Dr. Anthony Fauci, the nation’s top infectious disease expert.

In the opening months of his presidency, Biden has put top priority on a robust response to the virus that has killed 559,000 Americans, with a vaccine campaign in which nearly 50% of adults have received at least one shot.

His actions have received generally strong reviews, and hesitancy toward taking the vaccine has gradually declined as inoculations have increased. With three vaccines in use in the U.S. and plenty of supply in the pipeline, Biden actually has received some criticism for not sharing more vaccines with other nations. The president said Tuesday’s action proved the wisdom of his approach.

“My message to the American people on the vaccine is, I told you all,” Biden told reporters after the announcement, adding that he “made sure we have 600 million doses” just from Pfizer and Moderna in the pipeline.

The Johnson & Johnson pause, which regulators say they hope to resolve within days, comes on the heels of production issues at the Baltimore plant that produces the J&J vaccine.

The White House, which got only about 12 hours’ notice that some sort of announcement was coming and did not have any advance warning about the substance of the FDA and CDC’s action, moved swiftly to minimize concerns about its impact. Aides recognized that they had to portray the decision as ensuring the “gold standard” of safety, to avoid feeding into vaccine hesitancy.

“I think it’s a very strong argument for safety actually,” Fauci said.

White House coronavirus coordinator Jeff Zients added that the pause by the agencies “should reassure the American public that they will be very diligent and conservative about how they approach the vaccines.”

They argued the pause proved the prudence of Biden’s cautious approach to promises around vaccine supply and delivery, as well as his administration’s reluctance to make commitments to share excess vaccine with the world because of concerns about potential setbacks such as this.

“They’re clearly trying to reassure people there will be supply, and it will be safe,” said former White House communications director Jennifer Palmieri. “You don’t want this to have happened, but in terms of what are your tools when it does, they used their best ones — the president, the most senior person who has credibility and the top experts — to do it.”

Due to supply issues, the J&J shot reflects just a small share of doses being administered, though it had been one of the most promising vaccines given its ease of administration and distribution. Zients said the U.S. still expects to take delivery of enough doses of the other two approved vaccines for every adult American to get their shots by the end of May. Moderna and Pfizer this week are delivering 28 million doses to the federal government — enough to exceed even the current 3 million shot-per-day pace.

Zients acknowledged that some states may have been caught off guard by Tuesday’s announcement but said that reflected the speed with which officials moved to address the safety concerns. He added it was proof of Biden’s commitment to “follow the science” in responding to the pandemic.

“We want the science agencies to lead with science,” Zients said, saying no one at the White House was involved in the decision to call for the pause. “There’s no reason for us to be involved in any of the scientific decisions, we bring nothing to the table.”

The agencies said Tuesday they were investigating unusual clots that occurred in six women, of the more than 7.2 million adults who’ve received the shot. One of the patients died and another remains hospitalized in serious condition.

Officials said the delay had as much to do with educating physicians about the unique way the clots have to be treated as their desire to study the exceedingly rare side effect. The usual treatment, with the blood thinner heparin, could lead to dangerous patient outcomes, they said.

Fauci, speaking at the White House, advised those who had recently gotten J&J shots not to “get an anxiety reaction, because remember it’s less than one in a million.” He added, “However, having said that, pay attention” to potential symptoms of the clot including severe headaches, abdominal or leg pain, and shortness of breath.

Dr. Mati Hlatshwayo Davis, an infectious disease physician at the John Cochran VA Medical Center and St. Louis Board of Health, said the J&J pause might affect overall vaccine confidence but the transparency was critical to boosting confidence in minority communities that have some of the lowest uptake of the shots.

“Today was such a sign of strength and of leadership and of improved direction toward rebuilding trust in these communities,” she said of the Biden administration’s forthrightness about the issue. “They came to us as soon as this information became available knowing what was at stake.”

“They’re trusting the American public, and this gives these communities a reason to trust them,” she said.