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NEW YORK — It is the worst of times in New York, but it is not so bad in San Francisco.

They are the two densest cities in America in terms of population. Yet, the disparate impact coronavirus has had on them this year is shocking.

As of May 10th, there were 14,753 confirmed deaths from COVID-19 in New York City, according to the NYC Health Department, and another 5,178 who probably died of the virus. That’s a total of 19,931 people dead from COVID-19 in New York City.

San Francisco has had 33.

That’s not a mistake. Since the COVID-19 pandemic began, the total number of deaths in San Francisco is 33. That is .165 % of New York’s total.

How is that kind of disparity possible?

“We’re scratching our heads,” Dr. Yvonne Maldonado told PIX11. “I just think that maybe it’s easier to distance here than it is New York.”

Dr. Maldonado is a professor of Pediatrics – Infectious Diseases at Stanford University whose research is focused on epidemiological virus vaccines.

“No one knows for sure,” said Dr. Thomas Giordano, the Chief of the Section of Infectious Diseases at the Baylor College of Medicine in Houston. But he pointed out there are some theories. “The size of the population is so much greater in New York. It had more opportunity to magnify because sheer numbers are larger there.”

New York City has about 8.4 million people — 18.8 million in the metro area and its density is 27,711 people per square mile — compared to San Francisco’s population of 896,000 — 3.3 million in the metro area) and 19,103 people per square mile.

NYC is far larger, far more populated and much denser than San Francisco. And San Francisco doesn’t have the same level of crowded mass transit. But that doesn’t explain the almost incomprehensible difference in COVID-19 deaths.

Epidemiologists have suggested that the fact San Francisco implemented social distancing sooner than New York may be a big factor, but it only was a matter of a few days.

Six Counties in the San Francisco Bay Area began so-called “sheltering in place” on March 17. California Gov. Gavin Newsom ordered it statewide on March 19. Gov. Andrew Cuomo issued a similar order for New York on March 20, taking effect on March 22. That’s only a five-day difference, but it may have been significant.

“Once it (COVID-19) gets in and it starts magnifying exponentially, a small difference at the beginning can translate into a huge difference days and weeks and months after,” said Dr. Giordano.

Giordano underscored that problem, noting that COVID-19 may have had many more entry points (more people) bringing it into New York than to San Francisco.

New York Gov. Andrew Cuomo made a similar point at his daily briefing on Monday.

“We had the virus that attacked us from Europe,” Cuomo said. “Nobody knew the virus was coming from Europe. Everybody is looking at China and the virus is coming from Europe. Why? Because by the time we moved the virus had traveled from China to Europe. And then people are getting on flights coming from Europe to New York.”

Cuomo said that meant 2 million travelers potentially brought the virus to the New York city area.

So, we wondered, did New York do anything “wrong?” “I don’t think so,” Dr. Maldonado said. “We think that there was early introduction here…I mean I really think it wasn’t a matter of wrong…It’ the nature of the density. It’s the type of work.”

She pointed out that San Francisco has a big tech industry. Those are mostly people who can work from home and a lot of companies implemented that process early on. Also important, with much less disease in the Bay Area, that means medical workers aren’t overloaded and so heavily exposed to the virus.

Dr. Maldonado said she believes there’s also been an impact because of West Coast sensibilities. “I think we just follow the rule out here. I think people are very careful about following the rules.”

Dr. Giordano suggested that social and income levels also may play a role. “Once a virus gets into the population it can take root there and grow, but it doesn’t get into all populations evenly. If it hits a different population in one city than the other and one population is less able to social distance, that could explain part of it…It didn’t get into San Francisco to the same extent. It hasn’t exploded there.”

“The introduction that came into New York was from the Milan, Italy-China connection which was later – much later – than what happened out here,” according to Stanford’s Dr. Maldonado. The question is, “Well, was the virus more virulent? But these viruses don’t look that different.”

But on April 30, a study was published on, a website run by the Cold Spring Harbor Laboratory where scientists can put out their work before it’s officially published so they can get feedback and criticism. The study found mutations in the COVID-19 virus since its initial spread from Wuhan, China.

It found one of the mutations “of urgent concern.” It’s a stronger form of the virus that began spreading in Europe in February and quickly became the dominant strain. In other words, the virus became more infectious and more dangerous.

So, PIX11 asked Dr. Maldonado, is it possible San Francisco got hit with the weaker form of the virus and the new stronger strain never took hold there? Meaning perhaps a stronger form overwhelmed New York? Could that explain the great difference between the way the cities were hit by COVID-19?

“It is possible, but this paper has not yet been peer-reviewed,” Dr. Maldonado told PIX11 in an email. “This new mutation may just represent a new circulating strain, but the clinical and immunology implications are still unknown.”

Where do we go from here and will we ever know why New York was hit so hard and San Francisco spared?

“You have to do genetic analyses of the different isolated strains and really in-depth analysis,” advised Baylor’s Dr. Giordano, who has been a leader in fighting the AIDS virus.

Dr. Maldonado said we can’t wait for a vaccine. It’s important to develop therapies to treat people with milder forms of the disease and keep them from spreading it or being hospitalized. “This is the cold virus, one of the cold viruses, that just happens to be lethal,” she tells PIX11.

“I think we need to learn more about what this virus can do,” Dr. Maldonado warned, “because we’re going to see it again.”

After all, Dr. Giordano said, “No one wants to be New York City as we move forward.”