51成人动漫

Are we in a second "wave" of COVID-19 or still in the first wave? Even now, epidemiologists aren't entirely sure.

The 1918 H1N1 "Spanish flu" pandemic is described as having but Stephen Morse, PhD, of Columbia University Mailman School of Public Health in New York City told 51成人动漫 that a "wave" is a biological phenomenon, and it's not clear how to determine if a wave has transpired.

"When we talk about waves of pandemics of influenza, it meant something fairly specific," he said, explaining how the virus swept around the globe, infecting the population, "then quiets down for a little while," before coming back again.

Julie Fischer, PhD, of Georgetown University in Washington D.C. agreed, telling 51成人动漫 there have been so few pandemics, so "it's not like we have tons of hard data and this happens all the time."

She added it's surprising how much we don't understand about seasonality of viruses, such as seasonal influenza that pops up in the winter: we can predict it will occur, but "we're not really good at understanding why the pattern happens."

"It's not geography per se, but has to do with the way human beings move around and interact with animals and other carriers in our environment that transmit viruses to us," Fischer said. "We have assumptions, but we don't have concrete data."

As there was no biological evidence available in 1918, Morse cited the 1957 flu pandemic, saying there was "good supposition that it may have undergone mutations that made it possible to infect populations it hadn't before."

The theory, he said, was that the infected population develops "some degree of herd immunity" to the existing virus, which then undergoes a minor genetic change that allows it to recirculate and reinfect the population.

But critical to the theory of "waves" is a "pause" in infections, where the virus dies down. And that hasn't happened yet to any notable extent with COVID-19, Morse noted.

"It's not relevant here, because I think we're still in the first wave," he said, adding that there are still plenty of susceptible people that have yet to be infected, and that any "pause" in the pandemic has been through measures "artificially designed to slow it down."

"If I go out on the street ... and I get infected, that's simply because I'm still susceptible. I see that as more of a reintroduction, more cases coming in from somewhere else ... rather than another wave," Morse said. "If it continues to go on, as it has, what you're doing is slowing it down and there will be more susceptible people."

Morse highlighted what happened in San Francisco in 1918, which implemented all the control measures the U.S. is using now for the COVID pandemic, such as wearing masks.

"When the first wave ended and they saw there were no new cases, they thought they had 'escaped.' They had mask-burning parties. To their great surprise, a few months later, the next wave comes by," he said.

And even if SARS-CoV-2 is mutating, he said, such changes appear to be happening regularly and are "not biologically significant." Morse pointed to the D614G mutation, which seems to make SARS-CoV-2 more transmissible, but it remains unclear "whether it's more virulent" or makes any difference in the disease that would be "significant."

Fischer said she thought the different peaks in cases had to do more with behavior rather than anything biological related to the virus, with no data yet to show "a huge biological change" in SARS-CoV-2.

"Kids go back to school, people move indoors and spend time in indoor spaces again. People are exhausted and fatigued of being disciplined about maintaining physical distance," she said. "The whole point of lockdown was initially thought to reduce rapid transmission of the virus so we didn't overwhelm the healthcare system. But the time wasn't well-used" to ramp up public health interventions, she said.

"If there's no better protection for [people] than to just wait ... that is a very, very frustrating experience for everyone living with these restrictions," Fischer said.

She pointed to the lack of diagnostic testing and contact tracing efforts, which would "let us manage what is clearly a months-long effort at a better pace."

Morse agreed that the COVID-19 diagnostics "haven't been very useful," nor have they been "appropriately scaled up or deployed." And despite all our technological advances from the beginning of the last century, masks and social distancing are still the main ways to control transmission.

"We're fighting the first major pandemic of the 21st century with the tools of 1918," he said.

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