Uptick in COVID-19 cases has U.S. talking about second wave. Here's what experts say.

For a few weeks in May the coronavirus seemed to be finally waning: the national case numbers, which had increased astronomically in the spring, had leveled off. The states had started the process of reopening.
Cases are now increasing again, raising concerns that a second wave has hit the United States.
NBC News contacted several experts who are investigating clinical pictures. Everyone agreed: No, this is not a second wave.
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A second wave of the coronavirus indicates that the first wave has come and gone. That didn't happen.
"We never made it out of the first wave," said Dr. David Weber, medical director for hospital epidemiology at the University of North Carolina medical center at Chapel Hill.
What is a wave?
Weber compared waves of infectious diseases to ocean waves. "When you're 10 feet on the shore and the wave hits you, it goes all the way back," he said. "Now you're on dry land with no puddle underneath."
But with COVID-19, he said, "We still have a big puddle there."
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The word "wave" comes from the curve that represents the number of people infected during an outbreak. As more people get sick every day, the curve increases. If fewer people get sick every day, the curve drops.
"Flattening the curve" - ​​that is, stopping the increase in the number of new daily cases and causing them to flatten but not necessarily to decrease - is important because it enables health systems to distribute resources so that they can don't be overwhelmed. The US as a whole sits there - on a plateau of new daily cases - while companies start to reopen.
"A second wave implies that the first wave has disappeared and reappeared," said Loren Lipworth, an epidemiologist at Vanderbilt University Medical Center. "I don't think we see that here in the United States."
Instead, the US appears to be going through a constant chain of smaller peaks. Lipworth referred to them as "waves of infection" rather than a big wave that has come and gone.
While cases have declined significantly in the hardest hit states of New York and New Jersey, they are increasing in states like Arkansas, Arizona and South Carolina.
These states "did not have much disease activity at the beginning of the pandemic, but are now experiencing an upswing," said Caitlin Rivers, epidemiologist at the Johns Hopkins Center for Health Security. In other words, their first waves are just beginning.
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Another way to test whether an area has survived the first wave of an infectious disease is to examine the spread of the community or the transmission of the virus, which cannot be attributed to a source.
Only if areas could get through a week or two without spreading the community would they qualify as the first wave, Weber said. In fact, community is still spreading across much of the country.
COVID-19 in the fall
It is possible that the current plateau will stay on the same course in summer without decreasing significantly, and then continue to rise this autumn when schools reopen and the annual flu season begins. This is not necessarily a "second wave", but an even bigger increase compared to the current series of smaller crests.
"There is a possibility that we will revive in the fall," said Rivers. "But there are many unanswered questions because we have never seen this virus before."
Scientists can only base predictions on previous pandemics such as the 1918 influenza pandemic.
The first wave of this infection was in July, when influenza viruses are generally not well transmitted due to higher temperatures and because people generally spend more time outdoors.
This wave largely subsided in August and September, but in a second wave the cases increased significantly in October and November 1918. The return of the disease was largely attributed to the fact that the authorities downplayed the importance of the virus and continued large public gatherings, particularly in Philadelphia.
As a result, 12,000 people died in Philadelphia. In contrast, immediate social distancing in St. Louis resulted in only 1,700 deaths.
In fact, the potential for a larger increase in COVID-19 will also depend on people's actions. In contrast to the actual ocean, there are ways to slow down the waves of the virus or at least to minimize its risks.
"If people are less compliant with physical distance and masks," said Weber, "we'll see more cases."
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