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The nation's top health officials testified before Congress Thursday as the U.S. enters a critical phase in its battle to emerge from the Covid pandemic.

White House health advisor Anthony Fauci, Centers for Disease Control and Prevention Director Rochelle Walensky, and the Biden administration Covid response chief science officer David Kessler faced at times heated questions before the House Select Subcommittee on the Coronavirus Crisis.

Their testimony comes after the Food and Drug Administration earlier this week recommended that states pause the use of Johnson & Johnson's one-shot vaccine after six women reported blood clots and one died.

The call to press pause on J&J vaccinations comes ahead of a crucial milestone in the country's immunization campaign, with nearly 50% of the U.S. adult population having received at least one vaccine dose. The U.S. is currently administering 3.3 million shots a day on average.

Walensky said the CDC is committed to transparency as it investigates the blood clot cases and will provide updates as they become available. Fauci indicated that a decision on whether to recommend resuming J&J vaccinations could come soon.

Fauci repeatedly clashed with GOP Rep. Jim Jordan on when life can return to normal. The White House health advisor said new infections need to fall well below 10,000 cases a day.

Fauci also said that the medical and scientific communities hope to develop a universal coronavirus vaccine that can cover all possible variants.

You can watch the testimony below:

Here are the key highlights from the hearing:

• Fauci: Universal Covid vaccine is the endgame
• Americans should expect a Covid booster shot, Kessler says
• CDC committed to transparency on J&J vaccine, Walensky says
• Fauci pushes back on study that found Pfizer, Moderna, AstraZeneca recipients had same rate of blood clots
• Fauci and Jordan clash over Covid health precautions

Clyburn tells members of Congress to lead by example in fight against Covid

Rep. James Clyburn, D-S.C., ended Thursday's hearing on the pandemic by encouraging his colleagues in Congress to keep adhering to social distancing guidelines.

"We've heard today what we must do to save lives," said Clyburn, chairman of the Select Subcommittee on the Coronavirus Crisis. "We must continue to wear masks and avoid crowds until all Americans have had an opportunity to be fully vaccinated."

"And we must overcome vaccine hesitancy so that all Americans benefit from these life-saving scientific breakthroughs — including those of us who the American people have given leadership positions, by their actions," Clyburn said.

"We ought to lead not by our words but by our deeds. Not just by precepts, but by examples. We ought to be an example."

Before adjourning, Clyburn said he would allow members five more days to submit additional questions to the health experts who appeared as witnesses.

— Kevin Breuninger

Fauci says the ultimate endgame is a universal coronavirus vaccine

Responding to Democrat Congressman Bill Foster's question about the next generation of vaccines, Dr. Fauci said that the ultimate endgame is a universal coronavirus vaccine.

Booster shots against dangerous variants like the one first discovered in South Africa are already being tested, but beyond that, Fauci says a universal coronavirus vaccine is the ultimate goal.

"There are a number of ways of doing that, we have important and new platform technologies and we believe for example that we can apply the mRNA technology to get to that goal of getting a broad response against all possible variants."

Fauci then said that these are activities that have already started with the help of funding from Congress.

—Rich Mendez

Fauci anticipates decision soon on J&J vaccine, calls shot very effective

Dr. Anthony Fauci defended the decision to recommend pausing the use of Johnson & Johnson's single-dose vaccine, and signaled that that halt may soon be lifted.

"Hopefully, we'll get a decision quite soon as to whether or not we can get back on track with this very effective vaccine," said Fauci, the nation's top infectious disease expert.

The Food and Drug Administration and the Centers for Disease Control and Prevention on Tuesday recommended that vaccine providers temporarily stop using J&J's shot, citing reports that six women developed a rare blood clotting disorder after their inoculations.

Experts raised concerns that the pause would make some people less likely to get vaccinated, which would slow the overall global efforts to fight the pandemic.

Fauci noted in his testimony before the House Covid subcommittee that a "relatively small number" of cases have been reported, compared with the nearly 7 million J&J doses that have so far been administered.

"The number as of now would be, like, less than one per million," he said.

But Fauci said the recommendation was made out of "an abundance of caution," partly in order to examine the cases more carefully and see if there are others out there. He said the pause was also advised in order to alert physicians, and potentially prevent them from treat patients incorrectly.

The approach to the blood-clotting disorder is often to use a certain anti-coagulant drug, but in this instance that drug might make the problem worse, Fauci said.

— Kevin Breuninger

'You're ranting again' — Fauci pushes back against Jordan grilling

Dr. Anthony Fauci once again clashed with Rep. Jim Jordan after the Ohio Republican asked the infectious disease expert when Americans should expect life to return to "normal."

Fauci told the committee life could return to normal for many Americans once new Covid-19 cases fall "well below" 10,000 per day, adding cases should begin to decline once more people get vaccinated.

Jordan quickly shot back at Fauci, saying the White House health advisor failed to give a proper timeframe of when a return to normalcy could happen.

"You didn't give us a time. Are we going to be here two years from now wearing masks?"

Fauci responded, "you're ranting again."

Jordan then said, "here's how it works Dr. Fauci, I get to ask you the questions."

"You're the highest paid official in the United States government," he continued. "You've given us your advice on baseball on dating apps on cruise ships. You told us zero masks, one mask, two masks, now back to one mask. I'm just asking you when is it going to end?"

Fauci said officials expect the pandemic to improve by mid-summer.

–Berkeley Lovelace Jr.

GOP Rep. Scalise repeatedly steers Covid hearing toward challenges at southern border

Rep. Steve Scalise, R-La., repeatedly turned the conversation on Covid toward the Biden administration's immigration challenges at the U.S.-Mexico border.

Scalise, the top Republican on the House subcommittee on the coronavirus, contrasted the administration's social-distancing recommendations with images of border facilities that are being overcrowded with migrant children.

Scalise held up photos showing tight-packed crowds of children seated on hard floors, which he said were taken inside those detention facilities.

He asked Dr. Anthony Fauci if, hypothetically, he heard about "4,000 people in a restaurant that's set for 250-person capacity ... would you consider that a major concern?"

"It would be a major concern, yes," Fauci replied.

Scalise said that those figures applied to a facility in Donna, Texas, that he and other Republicans visited within the past week.

Fauci said he considered that a major concern, too.

— Kevin Breuninger

Americans should expect booster shots to protect against variants, Kessler says

The Biden administration's Covid response chief science officer David Kessler said Americans should expect to receive booster shots to protect against coronavirus variants.

Kessler said currently authorized vaccines are highly protective but noted new variants could "challenge" the effectiveness of the shots.

"We don't know everything at this moment," he told the committee. "We are studying the durability of the antibody response. It seems strong but there is some waning of that and no doubt the variants challenge ... they make these vaccines work harder. So I think for planning purposes, planning purposes only, I think we should expect that we may have to boost." 

Late last month, the National Institutes of Health started testing a new vaccine from Moderna designed to protect against a problematic variant first found in South Africa.

In February, Pfizer and BioNTech said they were testing a third dose of their Covid-19 vaccine to better understand the immune response against new variants of the virus.

–Berkley Lovelace Jr.

Fauci locks horns with Rep. Jim Jordan: 'You're making this a personal thing'

Things turned personal as Fauci pushed back on a grilling from Rep. Jim Jordan, R-Ohio, about when Americans will be able to stop taking public health precautions, such as wearing masks and social distancing.

Jordan, who is known to take an aggressive stance in public hearings, pushed Fauci, the nation's top infectious disease expert, to be more specific about when people in the U.S. will "get their freedom back."

Fauci, noting the high rate of Covid infections occurring in numerous states, said, "my message, Congressman Jordan, is to get as may people vaccinated as quickly as we possibly can to get the level of infection in this country low that it is no longer a threat."

The two men quickly locked horns over the way the argument was being framed.

"You're indicating liberty and freedom," Fauci said. "I look at it as a public health measure to prevent people from dying and going to the hospital."

Jordan responded that Americans' freedoms have "been assaulted" during the pandemic.

"I don't look at this as a liberty thing," Fauci said. "I disagree with you on that completely."

"Well that's obvious!" Jordan shot back. He listed a number of lockdown restrictions that states put in place at various stages of the crisis, holding them up as examples of constitutional infringements.

The back-and-forth only grew more heated, as Fauci accused Jordan of "making this a personal thing, and it isn't."

"It's not a personal thing," Jordan said.

"You are. That is exactly what you're doing," Fauci replied. — Kevin Breuninger

Fauci downplays study that finds Pfizer, Moderna, AstraZeneca vaccines show blood clots at same rate

White House chief medical officer Dr. Anthony Fauci downplayed a study by researchers at the University of Oxford that found rare blood clots showed up in Pfizer and Moderna Covid-19 vaccine recipients at about the same rate as AstraZeneca.

Researchers at Oxford, which helped developed AstraZeneca's vaccine, said they found rare blood clotting known as cerebral venous sinus thrombosis, or CVST, occurred in four in a million people receiving the Pfizer and Moderna vaccines, compared to five in a million for the AstraZeneca vaccine.

The study has not yet been peer-reviewed.

Fauci said the study's conclusion was flawed, saying the researchers extrapolated data that wasn't in the study, thus making it appear the risk of blood clots was similar for each of the vaccines.

"It is impossible the way this study was designed and conducted to make that determination," he told the committee. "I believe the paper, which is in a preprint server, gets submitted to the classical scientific journals and undergoes a peer review that that confusion will be straightened out."

–Berkeley Lovelace Jr.

'We need to confront the reality of vaccine hesitancy,' top Covid expert says

David Kessler, the chief science officer working on the Biden administration's Covid response, emphasized the need to address vaccine hesitancy.

"The point that I want to stress is that nothing, nothing should detract from the fact that Americans need to get vaccinated," Kessler said in his opening statement to the House coronavirus subcommittee.

Kessler said he's prepared to discuss the Food and Drug Administration's recommendation this week that states temporarily stop using Johnson & Johnson's Covid shot. Experts fear that move will exacerbate vaccine-skeptical attitudes and possibly slow down the push toward herd immunity.

"I hope we can all agree that it's important that our fellow citizens get vaccinated and that we help ease the minds of those who are considering getting vaccinated," Kessler told the committee, but "we need to confront the reality of vaccine hesitancy."

The best way to help people overcome their concerns, he said, "is to be transparent with them about the safety about these products."

— Kevin Breuninger

CDC Director Walensky says transparency top priority as J&J vaccine on pause

CDC Director Rochelle Walensky said the agency is committed to safety and transparency in reviewing data on Johnson & Johnson's single-shot vaccine after six women developed blood clots and one died.

"Vaccine safety is a top priority and we take all reports of adverse events following Covid-19 vaccinations seriously," Walensky said.

The CDC and FDA recently recommended a pause in administering the Johnson & Johnson vaccine while the agencies review data and assess significance around adverse events. Dr. Fauci recently said that health regulators plan to thoroughly investigate and "find some common denominators among the women who were involved."

"CDC and FDA are committed to remaining transparent through this process and will provide updates as they are available," she said. Walensky added that the CDC and FDA is working to "build trust in the vaccine, the vaccinator and the vaccination system."

—Rich Mendez

Fauci says most prevalent Covid variant in U.S. is 'well covered' by vaccines

Dr. Anthony Fauci said Covid vaccines are effective against strains of the virus that are spreading in the U.S.

Fauci, in his opening remarks, stressed that "we are in a race between vaccinating as many people as quickly and as expeditiously as we possibly can, and the threat of the resurgence of viruses in our country."

But the "good news," he said, is that the highly contagious B.1.1.7 variant, now the most common Covid strain in the U.S., is "very well covered by the vaccines that we are using."

Even with other variants, "if the vaccination doesn't protect against initial infection, it protects against severe disease," Fauci added.

— Kevin Breuninger

GOP Rep. Steve Scalise criticizes 'ineffective' lockdowns

GOP Rep. Steve Scalise criticized the lockdowns put in place last year to curb the spread of the virus, saying the actions by federal and state officials caused children to miss school and businesses to permanently close.

"Far too many Americans have been thrown out of work because of selective, ineffective lockdowns," said Scalise, a representative for Louisiana and the ranking member on the committee.

He also praised former President Donald Trump's vaccine program Operation Warp Speed and the pharmaceutical industry for "delivering the fastest vaccine in history."

"Through President Trump's leadership and his refusal to be told no, that led to extraordinary speed, warp speed to use his term in getting vaccines in the lab and into the arms of over 100 million Americans," he added.

–Berkeley Lovelace Jr.

Clyburn to hearing participants: Mask up or shut up

House Majority Whip James Clyburn, D-S.C., the chairman of the Covid panel, issued a warning at the start of the hearing: Anyone attending in person has to mask up if they want to speak.

The hearing on U.S. vaccination progress is being conducted in a "hybrid" setting, with some participants appearing in person at a congressional hearing room in Washington, and others speaking via videoconference.

"Since some members are appearing in person, let me first remind everyone that pursuant to the guidance from the House attendant physicians, all individuals who are attending this hearing in person must wear a face covering," Clyburn said.

"Members who are not wearing a face covering are not permitted to remain in the hearing room and will not be recognized to speak," he said.

In addition to examining the Biden administration's vaccination efforts, the hearing is also set to focus on the need for people to wear masks and follow social distancing measures.

— Kevin Breuninger

U.S. averaging 3 million shots per day pace as nearly half of adults have received at least one dose

The U.S. is averaging 3.3 million daily vaccine doses reported administered over the past week, according to data from the Centers for Disease Control and Prevention. The country has maintained a daily average above 3 million for eight straight days.

About 37% of the total population, and 48% of those aged 18 and older, have received at least one dose of a Covid vaccine.

U.S. officials say the halt in use of Johnson & Johnson's vaccine will not slow down the country's vaccine rollout, noting there is enough supply from Moderna and Pfizer to continue the current vaccination pace.

The Johnson & Johnson vaccine makes up about 7.5 million of the 195 million total shots given to Americans thus far, according to the CDC. Roughly 10% of the more than 76 million people who are fully vaccinated have received the single-shot J&J vaccine.

The country is reporting about 71,200 daily new Covid cases, based on a seven-day average of data from Johns Hopkins University. That is far below the nation's winter peak but similar to levels seen during the summer surge, when average daily cases topped out at more than 67,000.

—Nate Rattner

More young people are ending up in the hospital as variants spread

Doctors told CNBC they are seeing a rise in the number of young people admitted to the hospital with Covid-19. They attributed the worrying trend, in part, to the highly contagious B.1.1.7 variant.

Young people are "getting infected more frequently because of the contagiousness" of the strain, said Dr. Paul Offit, a physician at Children's Hospital of Philadelphia.

CDC Director Dr. Rochelle Walensky said last week B.1.1.7 variant, the strain first identified in the U.K., is now the most common Covid strain circulating in the U.S.

The U.K. identified B.1.1.7, which appears to be more deadly and spread more easily than other strains, last fall. It has since spread to other parts of the globe, including the United States, which has identified 20,915 cases across 52 jurisdictions as of last week, according to the CDC. However, health experts say that number is likely much higher.

Even as the pace of vaccinations picks up, the highly contagious variants could potentially stall the nation's recovery from the pandemic, U.S. health officials have warned.

Additionally, young adults, some of whom have not been vaccinated yet, may be at risk of more severe cases. Hospitals are seeing more and more younger adults in their 30s and 40s admitted with severe cases of Covid-19, Walensky said. "Data suggests this is all happening as we are seeing increasing prevalence of variants, with 52 jurisdictions now reporting cases of variants of concern."

Walensky previously warned that traveling for spring break could lead to another rise in cases, especially in Florida where the variant was rapidly spreading.

"I'm pleading with you, for the sake of our nation's health," Walensky said at a briefing last month. "Cases climbed last spring, they climbed again in the summer, they will climb now if we stop taking precautions when we continue to get more and more people vaccinated."

– Berkeley Lovelace Jr.

J&J vaccine remains on pause after CDC panel says it needs more data

A Centers for Disease Control and Prevention advisory panel on Wednesday decided to postpone a decision on the use of Johnson & Johnson's Covid-19 vaccine while officials investigate six cases of women developing a rare but potentially life-threatening blood-clotting disorder.

The CDC's Advisory Committee on Immunization Practices voted unanimously to reconvene in a week, when it will decide what it will recommend to the CDC on J&J's vaccine.

A day earlier, the Food and Drug Administration and the CDC advised states to temporarily stop using the single-shot vaccine "out of an abundance of caution" after six women developed cerebral venous sinus thrombosis, or CVST. One of the women has died.

The postponement means the pause on J&J's vaccine will remain in effect.

U.S. health officials will likely though face questions from lawmakers on the J&J shot. Earlier this week, health officials had said the pause on the use of the vaccine might last only a matter of days, depending on what they learn in their investigation of the cases.

CVST is a rare form of a stroke that happens when a blood clot forms in the brain's venous sinuses. It can eventually leak blood into the brain tissues and cause a hemorrhage.

White House chief medical advisor Dr. Anthony Fauci said Tuesday the pause would give U.S. health regulators the time they need to thoroughly investigate the cases and "find some common denominators among the women who were involved."

–Berkeley Lovelace Jr.