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Why New York’s Last COVID Surge Was Far Less Deadly Than Its First

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For those who find themselves stuck inside worrying about the new variants of COVID-19 going around, the second wave of the virus in New York City might feel like deja vu.

Yet in some ways, this new surge has been much milder than the first. Far fewer New Yorkers have been hospitalized or died from COVID-19 this fall and winter than last spring, even though the number of total cases over the last three months was 40% more than the opening stanza of the pandemic. As the winter wave overwhelmed hospitals nationwide and thrust America’s death toll toward 500,000, medical centers in New York have been able to handle the surge.

So, what has changed? The fact that severe outcomes are less common raises thoughts of the city nearing herd immunity, but hospital leaders and infectious disease experts say the life-saving switch is due to more testing, better knowledge of the disease, and stronger preparation.

Better Medicine

“We look at it in our breakdown of data as three phases,” said Dr. David Reich, president and chief operating officer of Mount Sinai Hospital. Spring saw a massive surge of COVID-19 patients before cases slowed–but didn’t cease–over the summer. October ushered in a second flood of cases that began cresting in early January.

But mortality rates in New York City steadily declined after peaking in May at 11%. The case-fatality rate kept dropping even during the last surge, and by early February, was down to 4%.

“There are a few possible reasons for that,” Reich said. “The first is that in the spring there was just nothing in the way of therapeutics and we had no idea what to do. People were given drugs that turned out to be useless like hydroxychloroquine and azithromycin and a few others.”

Now, Reich said, health care providers have a better sense of what works, even though research on certain practices and medicines remain ongoing. For instance, Mount Sinai has started giving some patients blood thinners because its staff observed clotting in a portion of COVID-19 patients.

“Even though the literature is still evolving, it looks like at least a subset of patients do better with anticoagulation,” Reich said. Similarly, he said, “The drugs people commonly refer to as steroids…seem to be effective to a certain extent in patients who are more advanced in the disease.”

Better Preparation

Another factor in improved outcomes is that hospitals are less overwhelmed this time around because they are better prepared.

Per state criteria, hospitals had to maintain a certain number of empty beds in order to have surge capacity for a second wave. And hospital systems have also implemented new plans for moving patients between facilities in order to balance the patient load.

NYC Health + Hospitals, the city’s public hospital system, transferred nearly 500 patients among its 11 hospitals between November and the end of January.

This “steady movement of patients has helped the system manage capacity as facilities convert units to COVID-19-only units or move into the additional surge spaces that are part of our plan,” Dr. Mitchell Katz, President and CEO of NYC Health + Hospitals, wrote in a January 28th report to the hospital system’s Board of Directors.

“[In the spring], there weren’t enough critical care facilities in many circumstances to take care of acutely ill patients, so on top of everything else, the overwhelming of the hospital system was one of the contributing factors [in patient outcomes],” Reich said.

Katz noted that the city health system didn’t see the same spike in COVID-19 patients as it did in the spring, but rather a steady increase over recent months, which “has made this surge much different and more manageable.”

Patients arriving at the hospital are also generally less sick than they were at the start of the pandemic, Katz said. He noted that this, “combined with new therapeutics and other interventions, has reduced mortality significantly.”

Widely available testing for COVID-19 has likely made a difference in transmission and hospitalization rates.

“It’s the first step to actually interrupting further spread,” Dr. David Chokshi, the city health commissioner, said in December, adding, “Once someone tests positive, we very quickly help them isolate.”

A much smaller share of COVID-19 tests are coming back positive now than in the spring, although that figure is impacted by the fact that, early on, the few tests that were available were primarily given to people who were already experiencing severe COVID-19 symptoms.

Herd Immunity? Not quite yet.

Fewer positive tests and lower rates of severe symptoms raise the question of whether the New York region is close to achieving herd immunity. The more immune systems build defenses against COVID-19, the closer a community comes to interrupting the coronavirus’s ability to cause worse outcomes or spread from person to person. The vaccine campaign is aiding this quest, but a number of New Yorkers gained immunity last spring when the virus swept through essentially unimpeded.

“If there were no immunity by natural infection, we would be seeing a lot more people who have already been infected getting infected again,” said Jeffrey Shaman, an infectious disease specialist at Columbia University.

It’s still unclear exactly how much natural immunity comes with a coronavirus infection, or how long that immunity lasts. But so far, reinfections have been extremely rare, with one recent large-scale study of U.K health care workers reporting a rate of 1%. Among this group, the researchers estimated that prior infection reduced the odds of a second bout by 83%. While there have been documented instances of people getting reinfected with COVID-19, for the most part people getting sick now did not have it before, experts say.

As of February 19th, about 684,630 people have had confirmed cases of COVID-19 in New York City, but Shaman and other infectious disease experts say these diagnostic tests likely only capture a fraction of total cases. Based on a predictive model Shaman developed with other researchers at Columbia University, the total number of cases in New York City may be five times that amount.

That would mean some 2.8 million people in the city, or about a third of the population, have already been infected. Viviana Simon, a professor of microbiology at the Icahn School of Medicine at Mount Sinai, says her research lab also reports an estimate in that ballpark, with between 20% and 25% of city residents infected. Add another 400,000 city residents who’ve been fully vaccinated as of February 22nd, and you’re only tacking on another 3 percent or so.

“That’s not enough for herd immunity. It needs to be at least 75% to 80% for herd immunity, so vaccines will be essential for us,” Simon said.

Simon and Shaman attribute the milder second surge primarily to an increased volume of testing, meaning cases can be caught earlier before the disease spreads, and clinical interventions at hospitals. Better compliance with measures like social distancing and mask wearing may also have made a difference.

“The problem is that in winter the virus is more transmissible,” Shaman said. “It innately appears to transmit more efficiently in drier, colder air and people are indoors more and may be more complacent with controls.”

He said it’s still unclear whether COVID-19 will end up being a seasonal virus like the flu or follow another pattern.

Reich said that while the second wave hasn’t been as bad and Mount Sinai’s surge has already plateaued, it hasn’t been a picnic either. He added that more research on effective treatments is still needed because it is “still a scary disease” that kills one of every 10 hospitalized patients. “I wouldn’t want to take those odds for anyone I love,” Reich added.

“It’s hard on staff because it’s just such a long marathon for them,” he said. “There’s no light at the end of the tunnel just yet.”


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