A report by the U.S. Centers for Disease Control and Prevention says emergency room visits for non-coronavirus illnesses plummeted in April at the peak of the pandemic.

The agency released an analysis Wednesday that the declines were greatest among children 14 years old and younger, women and for people living in the U.S. northeast region. The CDC noted a steep drop in the number of people seeking emergency care for chest pain, including heart attack, along with declines in children needing help for conditions like asthma.

The United States has the world's largest number of confirmed COVID-19 cases with more than 1.8 million infections, with the death toll now topping 107,175.

The New York Times reports the Trump administration has selected five companies as the most likely candidates to produce a coronavirus vaccine. The companies have been identified as Massachusetts-based Moderna; AstraZeneca, which is partnering with Oxford University; and the pharmaceutical giants Johnson & Johnson, Merck and Pfizer.

The Times quotes a government official as saying the White House will announce the decision in the next few weeks.

Dr. Anthony Fauci, the country's top infectious disease expert and the head of the National Institute of Allergy and Infectious Diseases, told the Journal of the American Medical Association (JAMA) Tuesday he is "cautiously optimistic" that scientists will come up with an effective vaccine by the start of 2021, saying he hopes to have "hundreds of millions of doses." But he added, "there's never a guarantee."

"It could take months and months and months" before researchers find out if a vaccine works, Fauci said.

Fauci also warned that a new vaccine may not provide long-term immunity against COVID-19, the disease caused by the coronavirus.

"When you look at the history of coronaviruses, the common coronaviruses that cause the common cold ... the durability of immunity that's protective ranges from three to six months to almost always less than a year," he said. "That's not a lot of durability and protection."

Meanwhile, researchers at the University of Minnesota say hydroxychloroquine, the treatment that President Donald Trump highly touts as an effective COVID-19 treatment, does not keep healthy people exposed to the virus from getting sick.

The report in The New England Journal of Medicine says the drug was no more effective than a placebo in clinical trials.

The scientists carried out their tests on 800 people exposed to someone with the coronavirus.

Hydroxychloroquine is a drug used to treat malaria, which Trump called a "game-changer" in the fight against COVID-19. He claims to have taken the drug himself.

But some doctors say the drug could have serious side effects, including heart rhythm problems or even death.

The World Health Organization has suspended the use of hydroxychloroquine in tests for a coronavirus treatment. France has outlawed its use altogether.