A lot went wrong during the coronavirus pandemic as the virus tore through a polarized nation and public health leaders, policymakers and elected officials struggled to respond.

Chronic underinvestment in public health at the federal, state and local levels only made things worse. All told, more than 1.1 million people have died of COVID-19 in the United States, and more than 1,000 are still dying each week.

More than three years after the Trump administration declared the virus a public health emergency in January 2020, the government's pandemic response is now entering a new phase. On Thursday, the Biden administration will allow the emergency declaration to expire, offering a moment to take stock of how the nation responded to the worst public health crisis in a century.

Here are some lessons from the country's fight against the virus.

Get the messaging right.

Public health experts say that when managing an infectious disease outbreak, communication is not part of the response. It is the response.

The coronavirus pandemic showed that confusing messaging can worsen the spread of disease and erode faith in public health institutions. But messaging during a pandemic is a tricky business. The science is often changing, sometimes day by day, and instructions from public health officials — to mask or not to mask? — must change as well, which can create confusion and a lack of trust.

The key, experts say, is for public health leaders to bring their audience along with them by explaining that the guidance they are giving today may change tomorrow — and then acknowledging that what they said yesterday might have been wrong.

"When you're in a daily conversation with the public, you can explain those mistakes, what you've learned from them," said Dr. Richard Besser, a former acting director of the Centers for Disease Control and Prevention during the Obama administration. "You can own them."

Make it easy to share data.

The CDC was hamstrung during the pandemic by antiquated data systems and inconsistent data sharing between the federal government, states and health providers. And unlike Britain and Israel, which have national health care systems, the United States has no mechanism for a free flow of data among public health agencies and private providers.

Responding to a quickly mutating virus that poses different risks to different populations requires better and faster data, experts said.

"We were in the embarrassing position of having to call up the U.K. and Israel or South Africa to find out was going on — how many people were getting infected with this new infection, what the variant was," said Dr. Anthony Fauci, who helped lead the pandemic response under both the Trump and Biden administrations. "How many people were getting vaccinated, and what was the effect of those data? We literally had to wait months instead of getting it in real time."

Michael Osterholm, the director of the Center for Infectious Disease Research and Policy at the University of Minnesota, cited school closures as an example where real-time data would have helped.

Some coronavirus variants were more lethal to children than others, he said, adding that if officials had had access to timely data on the effects of the virus on children, they might have been able to tailor school closures to when students were most at risk.

"We need instantaneous data to know what's going on," said Osterholm, who advised President Joe Biden's transition team. "And as conditions change, we have to change."

Think carefully about school closures.

School closures have been a particularly contentious topic, but many experts now agree that some schools were closed for too long and that abruptly removing millions of children from U.S. classrooms has had harmful effects on their emotional and intellectual health.

Both Fauci and Dr. Ezekiel Emanuel, a professor of medical ethics and health policy at the University of Pennsylvania, said the pandemic had shown that officials should think carefully about school closures and keep them as limited as possible. Both said better indoor air circulation might be one way to safely keep schools open.

"One of the things we've learned is that we closed schools much longer than other countries, and we've had this terrible impact on educational attainment, and we have seen the test scores go down," said Emanuel, who also advised Biden's transition team.

Fauci said that early in the pandemic, "at a point when the hospitals were literally a day or two from being overrun," closing public places such as restaurants, bars and schools was important for keeping health care systems operating by slowing the spread of the virus.

"But once you put a damper on the acceleration," he said, "then you need to really examine how we keep the kids in school safely."

Stockpile vital supplies.

In the early months of the pandemic, front-line health workers faced dramatic supply shortages, forcing them to reuse face masks, wear ill-fitting personal protective gear or go without such equipment altogether.

The federal government has substantially expanded its reserve of pandemic supplies since, giving it a head start in responding to another devastating coronavirus wave or a different viral outbreak that would require similar resources.

Before the pandemic, government purchases for the Strategic National Stockpile were heavily weighted toward protecting against bioterror agents like anthrax. In March 2020, the stockpile had 13 million N95 masks. As of early this month, it had 352 million. In the same period, the number of ventilators grew to about 150,000 from 12,700.

Invest in vaccines early.

As a model for responding to future pandemics, experts point to Operation Warp Speed, the Trump administration's coronavirus vaccine development program. The initiative brought effective vaccines to Americans in record time — in part, Fauci said, because the federal government had spent years investing in basic scientific research.

Federal officials in the Warp Speed program made enormous bulk purchases of shots that were still in development. The federal government funded or supported clinical trials run by Moderna and Pfizer, the manufacturers of the two widely used coronavirus shots. And it lent expertise to the companies with clinical trial specialists, public health researchers and budget experts.

Quickly set up large randomized trials.

Early treatments for the virus such as hydroxychloroquine and convalescent plasma were authorized by the Food and Drug Administration without strong data from large randomized controlled trials — considered the gold standard of evidence used by regulators to clear drugs and vaccines.

Trials for treatments stalled because of a lack of funding or participants. Scientists, physicians and federal regulators relied on foreign data, such as a British study on dexamethasone, a steroid used to treat COVID-19.

"Britain set up large randomized trials with very loose entry criteria, thousands of patients," Emanuel said. "Within 30 to 60 days, we learned that steroids actually saved people who were hospitalized or very sick."

Dr. Walid Gellad, a drug safety expert at the University of Pittsburgh, pointed to a current trial being conducted by British researchers that he said would soon deliver results on the effectiveness of Paxlovid, Pfizer's antiviral drug for COVID-19 that is widely used in the United States.

"We didn't have the infrastructure to collect data we needed to make decisions," he said of the U.S. pandemic response.

But don't rely only on vaccines.

Vaccines proved to be the most effective bulwark against hospitalization and death from COVID-19. But attention to vaccination often overshadowed efforts to develop and deliver treatments, public health experts said. Antibody medications critical for immunocompromised Americans are no longer cleared for use by the FDA, and experts say more antiviral drugs are needed.

The Biden administration has focused heavily on deploying booster shots, which have had steadily fewer takers since an initial round was authorized in autumn 2021. But other strategies meant to prevent the spread of the virus, such as improving indoor air quality, have received comparatively modest attention.

"The myopic focus on vaccines alone at the exclusion of other areas that are really low-hanging fruit for a much superior response. It's like saying you're going to build a house with one wall or without a roof," said Dr. Luciana Borio, a former acting chief scientist at the FDA who advised Biden's transition team.