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September 23, 2021

Is the worst of the delta surge over? Why some experts are cautiously optimistic.

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    A new analysis from modelers at the Covid-19 Scenario Modeling Hub predicts the country will see a steady decline in new coronavirus cases through next March, Rob Stein and Carmel Wroth report for NPR's "Shots"—a scenario that suggests the worst of the delta surge may be over.

    How much worse will the 'delta surge' get? Watch these 7 factors.

    Covid-19 cases could decline steadily through March

    According to Stein and Wroth, the new analysis from the Covid-19 Scenario Modeling Hub, whose researchers advise CDC, suggests the delta surge may be peaking nationally, and that new cases and deaths will likely begin decreasing steadily through March 2022.

    In the analysis—which combined nine mathematical models from different research groups—modelers developed four potential scenarios for the next six months. These scenarios take into account varying potential levels of childhood vaccinations and whether a new, more infectious variant will emerge.

    According to Justin Lessler, a researcher at the University of North Carolina who helps run the Modeling Hub, the most likely scenario is that children get vaccinated and a new superspreading variant does not emerge.

    In this scenario, the combined model predicts new cases will slowly, but steadily, decrease from current levels of 140,000 daily cases to around 9,000 daily cases by next March. In addition, deaths from Covid-19 would decrease from around 1,500 a day to fewer than 100 a day by the same time. Researchers also predict that there will not be a winter surge in cases, as was seen in 2020.

    According to Stein and Wroth, the model's projected case and mortality rates are similar to those seen in late March 2020 when the pandemic first began to surge in the United States.

    Regional variation, late surges still possible

    However, Lessler noted there is a "wide range of uncertainty" in the models.

    While the most likely scenario predicts there will not be a winter surge in cases, another surge—including one where cases continue to rise to as many as 232,000 a day before declining—is possible.

    In addition, the emergence of a new, more contagious variant could lead to far worse case numbers, Stein and Wroth report, with the Modeling Hub predicting just under 50,000 cases a day by next March if this happens.

    "We have to be cautious because the virus has shown us time and time again that new variants or people loosening up on how careful they're being can lead things to come roaring back," Lessler said.

    William Hanage, an epidemiologist at the T.H. Chan School of Public Health at Harvard University, agreed the models show a "fair amount" of uncertainty and said he would be "concerned about interpreting these in an overly optimistic fashion for the country as a whole."

    In particular, Hanage noted that the worst surge of Covid-19 cases in the United States last year occurred midwinter, when cold weather led to more people spending time indoors. According to Stein and Wroth, both Hanage and Lessler said there will likely be regional variation in Covid-19 cases.

    For example, some states could continue experiencing surges for a few more weeks, while places with cold winter weather may be at risk of seeing increases in cases later in the year. "If you look at the seasonal dynamics of coronaviruses, they usually peak in early January. And in fact, last year we saw a peak like that with SARS-CoV-2," Hanage said.

    Researchers are cautiously optimistic

    Despite the uncertainty in the models, Lessler said he is hopeful the most optimistic prediction will be the most likely.

    "I think a lot of people have been tending to think that with this surge, it just is never going to get better. And so maybe I just need to stop worrying about it and take risks," he said. "But I think these projections show us there is a light at the end of the tunnel."

    According to Lessler, there should be enough immunity in the United States—from both vaccination and exposure to the coronavirus—that cases should not continue to surge.

    "The biggest driver is immunity," Lessler said. "We've seen really big delta waves. The virus has eaten up the susceptible people. So there are less people out there to infect." And while the virus is still fighting back, "immunity always wins out eventually," he said.

    However, coronavirus transmission will continue to be high for a while, Stein and Wroth report, so safety measures are still necessary until the number of new cases decreases to moderate levels.

    According to Natalie Dean, an assistant professor of biostatistics at Emory University, there will still be "a lot of cases and death," even if a decline is seen in the coming months. This means that it is necessary to vaccinate everyone who is eligible to prevent further deaths, Stein and Wroth report.

    "Any of us who have been following this closely, given what happened with delta, are going to be really cautious about too much optimism," Lessler said. "But I do think that the trajectory is towards improvement for most of the country." (Stein/Wroth, "Shots," NPR, 9/22)

    How much worse will the 'delta surge' get? Watch these 7 factors.

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