The seven-day average of daily cases as of Monday was 172,000, its highest level of this surge even as the growth rate is slowing and cases are headed down in most states, according to data compiled by the Covid Act Now tracker.
But more than 1,800 people are still dying a day, and over 100,000 remain hospitalized with severe Covid -- a grim reminder of the challenges authorities have faced in getting enough Americans vaccinated in the face of misinformation and a polarized political climate.
Bhakti Hansoti, an associate professor in emergency medicine at John Hopkins University and expert in Covid critical care, told she saw the US following a similar trajectory to India.
Countries in western Europe have also seen similar downturns in their Delta surges. But while Hansoti breathed a sigh of relief when the spring wave ended, "I'm a little hesitant this time around," she admitted.
The possible emergence of newer variants of concern and the advent of colder weather leading to more socialization indoors could lead to a rebound, "unless we learn from the lessons of the fourth wave."
Angela Rasmussen, a virologist at University of Saskatchewan in Canada, added she was not certain the fourth wave was over. "If you look at the fall-winter wave, there were periods in which there was a steep exponential increase, and then it looked like it was falling -- and then there would be another increase."
To ensure gains are sustained, rapidly increasing the number of people vaccinated is vital. Currently 63.1 percent of the eligible population over-12 are fully vaccinated, or 54 percent of the total population.
This places the United States well behind global leaders like Portugal and the UAE (81 and 79 percent fully vaccinated), despite its abundance of shots. The administration of President Joe Biden last week announced a number of new measures to ramp up the immunization campaign, including new vaccine requirements on companies of over 100 employees, but the impact is yet to be clearly seen.
Beyond vaccinations, experts want to see other interventions continue. Thomas Tsai, a surgeon and health policy researcher at Harvard, said hotspots need to follow through on masking, adding that the US should also look to other countries that have adopted widespread rapid testing for schools and businesses.
Such tests are available either for free or at a very nominal cost in Germany, Britain and Canada but remain around $25 for a two-pack in the US, despite the Biden administration's efforts to drive costs down through a deal with retailers.
Of course, the impact of all measures depends on their uptake, and in this regard, a clear and consistent pattern has emerged of two Americas: liberal-leaning regions are far more compliant than conservative.
Prior to the Delta wave, some experts declared that, between the percent of people vaccinated and those who had gained immunity through natural infection, the country was approaching the point of herd immunity.
Rasmussen said those predictions had proven incorrect and it remained too early to say when this threshold would be reached. "There are still parts of the country where the adult vaccination rate is less than 50 percent," she noted.
Though Delta has out-competed all previous variants and is currently dominant, SARS-CoV-2 continues to evolve rapidly and virologists fear that more dangerous variants might emerge.
"I don't want to be a doomsayer, but I also want to have some humility, because I don't think we know a lot about the basic function of many of these mutations," said Rasmussen.
Still, experts are hopeful that vaccines will continue to blunt the worst outcomes for most people and look forward to their authorization in children under-12 in the months to come.
It's expected that certain populations like the elderly and those with weakened immune systems may need boosters as well as high community vaccination rates to protect them.
Rather than eradication, the goal has shifted toward taming the virus for vaccinated people such that in rare cases of breakthrough infections, the disease is more flu-like.
However, uncertainties remain: for instance, people with breakthrough Covid infections might still get long Covid.
Greg Poland, an infectious diseases expert at Mayo Clinic, predicted humanity would be dealing with Covid "well past the lifespan of the next many generations."
"We are still immunizing against aspects of the 1918 influenza virus," he said.