(CNN)Dr. Joseph Varon hasn't taken a day off in 214 days.
"It's not that I don't want to. But the patients keep on coming," said Varon, a critical care doctor and chief of staff at United Memorial Medical Center in Houston.
It used to be worse. After Covid-19 crushed the hospital earlier this year, his team juggled as many as 88 patients at once with the disease. But in the last few weeks, as few as 10 coronavirus patients needed their care.
"Then the last five days have been hell. We're getting a lot of patients. And the patients are coming in very, very ill."
The fall Covid-19 surge is gripping the US, and doctors expect the next few months to be the worst period yet.
Seven months into the pandemic, doctors and scientists have made major strides in learning how to better treat patients of this still-new disease. And that knowledge is a huge advantage.
For example, ventilators -- once widely used early in the pandemic -- are now used less frequently, as doctors have learned how they may injure Covid-19 lungs.
But in some places, nurses still don't have enough protective equipment. People keep flouting masks and social distancing. And rapid, at-home testing remains a pipe dream.
Here's where experts say the US stands as it enters the next phase of the Covid-19 pandemic.
Many Covid-19 patients who entered hospitals earlier this year did not make it out alive.
Since then, "the death rate per case ... has definitely dropped. And that's a tribute to modern medicine," epidemiologist Dr. Larry Brilliant said.
"We have tools in our arsenal now. We have ... dexamethasone, which we know works. We have convalescent plasma, which we believe works," he said.But as more patients survive, many are also stuck at the hospital with long-term complications.
"Before, people would come in when they were just dying. Now, we keep them alive. But many of them have very bad lung disease, and they will require long-term care," Varon said.
He said some treatments can work well, such as convalescent plasma therapy or remdesivir.
Convalescent plasma is a blood product that is taken from volunteers who have recovered from an illness such as Covid-19. That plasma has antibodies that can help stimulate an immune response in someone who is currently sick.
"The evidence on convalescent plasma as a treatment for severe cases of COVID-19 is promising but incomplete," Dr. Francis Collins, director of the National Institutes of Health, said in a written statement last month.
For now, the NIH treatment guidelines don't recommend for or against using convalescent plasma to treat Covid-19.
Remdesivir was found to speed recovery in moderately ill patients with pneumonia from Covid-19, according to Phase 3 clinical trial results published in August in the medical journal JAMA.
But this month, the World Health Organization said remdesivir has "little or no effect on mortality" for patients hospitalized with Covid-19 and it doesn't seem to help patients recover any faster, either.
Despite the ever-evolving research, "we have learned a lot," Varon said. "What I do today is not what I was doing three, four months ago."
Blood thinners reduce deaths among coronavirus patients, study finds
Why ventilators might be bad for Covid-19
While states were scrambling to find ventilators earlier this year, Varon and other doctors now only use ventilators as a last resort when treating Covid-19 patients.
With many patients, "we learned that putting somebody on a ventilator is basically signing their death sentence," Varon said.
"We learned the hard way that putting pressure into your lungs in somebody that has damaged lungs, like Covid patients, was creating more injury than benefit."
Brilliant said it's "good news" that hospitals aren't using ventilators as much on Covid-19 patients.
"Doctors are not shoving ventilators down people's throats quite as quickly. That's a wonderful thing," he said.
Now, doctors like Varon sometimes allow a concept known as "permissive hypoxemia." The NIH says hypoxemia, or a low level of oxygen in the blood, is common in Covid-19 patients.
"You know how everybody thinks that an oxygen (level) of more than 90% is good, and that's where you need to stay? We learned that because we were causing so much damage (with ventilators), maybe we should tolerate a little lower oxygen. So if it came down to 85%, we probably would be OK."
That's different from his previous methods with non-coronavirus patients, in which those with "85% (oxygen) gets a (breathing) tube. 89% gets a tube. So we learned that we can actually allow lower oxygen concentrations."
Doctors have also learned that laying patients facedown on their stomachs can help increase the amount of oxygen that's getting to their lungs.
The technique is called proning. Critical care specialists say lying on the belly seems help because it allows oxygen to get into the lungs more easily.
"We're saving lives with this," Dr. Mangala Narasimhan, regional director for critical care at Northwell Health in New York, said in April.
"It's such a simple thing to do, and we've seen remarkable improvement. We can see it for every single patient."
When patients lie on their backs, the weight of the body effectively squishes some parts of the lungs.
But "by putting them on their stomachs, we're opening up parts of the lung that weren't open before," said Dr. Kathryn Hibbert, director of the medical ICU at Massachusetts General Hospital.
While it's great that doctors can save more lives, "we're seeing the long-term effects of Covid," Varon said.
"We are now recognizing that they end up having some chronic lung issues. Their lung capacity is not what it used to be," he said. "The heart may or may not have issues. There's so many things, it's not even funny."