• The U.S. has officially recorded more than 100 million confirmed Covid cases, but the actual number is probably at least twice as high.
• As the U.S. enters the fourth year of the pandemic, the virus keeps mutating into more transmissible variants, making it even more difficult to control.
• About 400 people a day are still dying from the virus and about 5,000 are being admitted to the hospital daily.

The U.S. recorded more than 100 million formally diagnosed and reported Covid-19 cases this week, but the number of Americans who've actually had the virus since the beginning of the pandemic is probably more than twice as high.

Covid-19 has easily infected more than 200 million in the U.S. alone since the beginning of the pandemic — some people more than once. The virus continues to evolve into more transmissible variants that dodge immunity from vaccination and prior infection, making transmission incredibly difficult to control as we go into the fourth year of the pandemic.

The U.S. officially recorded more than 100 million cases as of Tuesday, just under one-third of the total population, according to data from the Centers for Disease Control and Prevention. The data isn't perfect and likely a huge undercount of the actual number of infections, scientists say. While it counts people who've tested positive more than once or caught Covid multiple times, it doesn't capture the number of Covid patients who were asymptomatic and never test or tested at home and didn't report it.

Dr. Tom Frieden, former CDC director under the Obama administration, estimates that the reported data reflects less than half of the actual total.

"There are have been at least 200 million infections in the U.S., so this is a small portion of them," Frieden said. "The question really is will we be better prepared for Covid and other health threats going forward, and the jury is very much still out on that," he said.

The CDC estimated last spring that nearly 187 million people in the U.S. had caught Covid at least once through February 2022, more than double the number of officially reported cases at the time. The estimate was based on a survey of commercial lab data that found about 58% of Americans had antibodies as a result of a Covid infection. The survey did not account for reinfections or antibodies from vaccination.

The CDC has subsequently recorded more than 21 million confirmed cases from March through Dec. 21 of this year, although this is an underestimate because people who use rapid tests at home are not picked up in the data.

The more than 21 million additional confirmed cases on top of the CDC's February estimate of about 187 million total infections gives a low-end estimate of more than 208 million infections since the pandemic began.

"It's really hard to stop this virus, and that's one of the reasons why we've shifted the focus to hospitalizations and deaths and not just counting cases," said Jennifer Nuzzo, an epidemiologist and director of the Pandemic Center at Brown University School of Public Health.

The U.S. has made significant progress since the darkest days of the pandemic. Deaths have dropped about 90% from the pandemic peak in January 2021 when more than 3,000 people were succumbing to the virus daily before widespread vaccination. Daily hospital admissions are down 77% from a peak of more than 21,000 in January 2022 during the massive omicron surge.

Despite this progress, deaths and hospitalizations remain stubbornly high given the widespread availability of vaccines and treatments. About 400 people are still dying a day from the virus and about 5,000 are admitted to the hospital daily. The virus is still circulating at what would have been considered a high level earlier in the pandemic, with nearly 70,000 confirmed cases reported a day on average, a significant undercount due to testing at home.

More than a million people have died in the U.S. from Covid since the pandemic began, more than any another country in the world.

"I think people have gotten hardened to it," Frieden said of Covid's toll. "Covid is a new bad thing in our environment, and it's likely to be here for the long term. We don't know how this will evolve, whether it will get less virulent, more virulent — have years that get better and worse."

White House chief medical advisor Dr. Anthony Fauci, who is stepping down this month, has said the U.S. can consider the pandemic over when Covid hospitalizations and deaths decline to a level similar to the burden from the flu.

For the first, the two viruses are circulating simultaneously at high levels. From October through the first week of December, flu killed 12,000 people while Covid took more than 27,000 lives during that period.

"We're still in the middle of this — it is not over," Fauci told the radio show "Conversations on Health Care" in November. "Four hundred deaths per day is not an acceptable level. We want to get it much lower than that."

Frieden said 95% of people who are dying from Covid aren't up to date on their shots and 75% of people who would benefit from the antiviral Paxlovid are not receiving it.

"We should celebrate these great tools we have, but we're not doing a good job of getting getting them into people and that would not just save lives, but reduce the disruption from from Covid," he said.

Dr. Ashish Jha, the White House Covid task force coordinator, has said people who are up to date on their vaccines and get treated when they have a breakthrough infection face almost no risk of dying from Covid at this point in the pandemic. Jha has called on the older Americans in particular, who are more vulnerable to severe illness, to get boosted so they have more protection during the holidays.

"There are still too many older Americans who have not gotten their immunity updated who have not gotten themselves protected," Jha told reporters at the White House last week.

Michael Osterholm, a leading epidemiologist, said new Covid variants will pose the biggest threat to progress the U.S. has made in 2023.

China has eased its stringent zero-Covid policy, which sought to crush outbreaks of the virus, in response to widespread social unrest during the fall. Infections are now soaring in the country, raising concern that Covid now has even more space to mutate.

The virus has continued to mutate into ever more transmissible versions of omicron over the past year, at the same time that immunity from vaccination or prior infection has waned off.

"We want to believe that after three years of activity, all the immunity that we should have acquired through either vaccination or previous infection should protect us," said Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. "But with waning immunity and the variants — we can't say that."