As the United States heads into flu season, Americans can't let up in the fight against the ongoing coronavirus pandemic, Dr. Anthony Fauci said Thursday.
Although the number of new daily cases of coronavirus in the U.S. has slowly been declining over the last two weeks, the country is still closing in on 200,000 deaths from COVID-19 and more than 6 million confirmed infections.
“We need to hunker down and get through this fall and winter because it’s not going to be easy,” Fauci said during a panel of doctors from Harvard Medical School.
Fauci, director of the National Institute of Allergies and Infectious Diseases, also spoke about the COVID-19 vaccine trials and the possibility of post-Labor Day surges, noting that as one region in the U.S. gets it under control, another hot spot emerges — and that spikes inevitably appear whenever states lift social distancing restrictions.
“It’s really quite frankly depressing to see that because you know what's ahead,” he said.
Fauci, one of the world's leading AIDS researchers since the 1980s, warned about the dangers of underestimating the virus. He compared the pandemic it to the early days of HIV when the epidemic started with a few gay men to decades later with tens of millions of deaths and more than 70 million people who have been infected.
“We've been through this before,” he said. “Don't ever, ever underestimate the potential of the pandemic. And don't try and look at the rosy side of things."
Fauci’s sobering comments about the need for doctors and scientists to approach COVID-19 with “humility” came a day after President Donald Trump was heard in an audio clip acknowledging in February that he had minimized the seriousness of the pandemic.
“I still like playing it down because I don’t want to create a panic,” Trump said a month later in a call with the journalist Bob Woodward, according to the clip on The Washington Post’s website. Trump has been criticized for his response to the virus.
Fauci didn't mention the president but did reflect on lessons learned.
"We've really got to realize that from Day One, you don't know it all," he said. "And you've got to be flexible enough to change your recommendations, your guidelines, your policies, depending upon the information."
Fauci said the vaccine trials are “progressing very well” and repeated his cautious optimism for a possible vaccine by the end of the year. He didn’t comment on the University of Oxford’s vaccine trial, which was paused this week after a participant in the U.K. developed a spinal cord issue.
When asked about the likelihood of a second wave of cases in the U.S., Fauci responded, “I don't talk about second surges because we're still in the first surge.”
While there are fears that influenza season, which begins in October, could overwhelm the nation's health care system, there is some optimism about the flu in Australia so far. Australia has experienced the “lightest influenza season in memory” due to social distancing measures that have been put in place for COVID-19, Fauci said.
But it’s unclear whether the U.S. will have similar luck.
“I don't know what's going to happen, and I'm not predicting,” Fauci said.
A version of this story originally appeared on NBCNews.com.