after a brutal summer surge the coronavirus is in retreat heres why rising immunity and modest changes in behavior may explain why cases are declining but much remains unknown scientists saycreditmike kai chen for the new york timesoct 14 2021after a brutal summer surge driven by the highly contagious delta variant the coronavirus is again in retreatthe united states is recording roughly 90000 new infections a day down more than 40 percent since august hospitalizations and deaths are falling toothe crisis is not over everywhere the situation in alaska is particularly dire but nationally the trend is clear and hopes are rising that the worst is finally behind usagainover the past two years the pandemic has crashed over the country in waves inundating hospitals and then receding only to return after americans let their guard downit is difficult to tease apart the reasons that the virus ebbs and flows in this way and harder still to predict the futurebut as winter looms there are real reasons for optimism nearly 70 percent of adults are fully vaccinated and many children under 12 are likely to be eligible for their shots in a matter of weeks federal regulators could soon authorize the first antiviral pill for covid19we are definitely without a doubt handsdown in a better place this year than we were last year said dr nahid bhadelia director of the center for emerging infectious diseases policy and research at boston universitybut the pandemic is not over yet scientists cautioned nearly 2000 americans are still dying every day and another winter surge is plausible given how many americans remain unvaccinated and how much remains unknown it is too soon to abandon basic precautions they saidweve done this again and again where we let the foot off the pedal too early dr bhadelia said it behooves us to be a bit more cautious as were trying to get to that finish linecrushing the curveimagecreditruth fremsonthe new york timeswhen the first wave of cases hit the united states in early 2020 there was no covid vaccine and essentially no one was immune to the virus the only way to flatten the proverbial curve was to change individual behaviorthat is what the first round of stayathome orders business closures mask mandates and bans on large gatherings aimed to do there is still debate over which of these measures were most effective but numerous studies suggest that collectively they made a difference keeping people at home and curbing the growth of case numbersthese policies combined with voluntary social distancing most likely helped bring the early surges to an end researchers saidand then the measures would be lifted maybe memories would fade said jennifer nuzzo an epidemiologist at johns hopkins universityeventually cases would rise again and similar patterns would play out businesses and local governments would reimplement restrictions while people who had begun venturing out into the world again would hunker down and mask upduring last winters surge for instance the percentage of americans who reported going