In the 15 months since Covid-19 was first detected on Martha’s Vineyard, more than 1,400 Island residents have tested positive for the virus, more than a dozen have been hospitalized and at least four have been transferred off-Island for medical care.

But none of the Island’s nearly 20,000 year-round residents have died of the disease that has killed more than 3.5 million people worldwide.

An epidemiologist and public health researcher at Georgetown University and the Harvard T.H. Chan School of Public Health who has been studying the spread of the virus on Martha’s Vineyard believes that number — zero — is miraculous, considering all the other ones mentioned before it.

“I think it’s quite remarkable [that the Island has not experienced a death],” said Dr. Michael Stoto, also Vineyard Haven summer resident, who has been working with Island health agents throughout the pandemic on a variety of projects, including school testing. “And there’s more going on than just that.”

Dr. Stoto, who plans to author a paper closely analyzing the Island’s Covid-19 numbers, wrote a commentary for the Gazette this week expounding on the Island’s unique relationship with the virus. In a telephone interview this week, he said state and national death tallies suggest the Vineyard has been extremely lucky — and that its low death tally is more than a statistical anomaly.

In the United States, which has a population of 331 million, there have been 589,000 deaths as of the third week in May. That equates to a death rate of 178 per 100,000 residents. In Massachusetts, which saw a case spike at the beginning of the pandemic when

testing was scarce, the death rate was higher: about 240 per 100,000 residents.

Part data scientist, part public health expert, Dr. Stoto used those proportions to calculate the Island’s expected death toll: 36 on the low end, 52 on the high end. Chilmark health agent Marina Lent, who worked with Dr. Stoto, used a more conservative number, calculating the state death rate from November onward — a period in which Island case rates have largely aligned with the rest of the commonwealth. That would have put the expected number of Island deaths around 27.

But the Vineyard has had none.

Even Nantucket has lost five residents to the virus — including a woman in her 50s who died on April 7.

“Let’s not exaggerate it, because it is already miraculous enough,” Ms. Lent said. “It points to something that can’t be easily explained by sheer luck. But the [lack of deaths] is a manifest fact. And it is fair to wonder why.”

Dr. Stoto has his theories. One of them involves an iceberg — or more literally, the notion that only a fraction of cases that occur are reported. During the beginning of the pandemic in New York city, epidemiologists suspected there were 10 times as many actual cases as reported cases. They now put that number at approximately four times the reported case load nationally.

But on the Vineyard, where asymptomatic virus testing has been widely available since last June, Dr. Stoto estimates that number is less than two times the reported case load. Although the Island’s positive case rate is disproportionately high relative to the mainland, it has a small underwater iceberg that at least partly explaining the lower death rate.

“My guess is that when we know about 1,500 cases reported, there probably hasn’t been that many more than 2,000 infections,” Dr. Stoto said. “And the reason for that is the people doing the contact tracing on the Island have been so good at it. Testing was heavily promoted here. And I don’t think we’ve ever had a serious situation with respect to Covid denialism.”

He also said widely available testing allowed health officials to detect the virus early and often, halting a large amount of asymptomatic spread. And he championed the ability of health officials to come together on public safety measures, like mask mandates and construction bans, filling a leadership vacuum left by the Island’s six balkanized townships.

He said the hospital and governor telling seasonal residents to stay home probably didn’t hurt, either. “We did a couple things right. We quickly developed a common operating procedure, and a situational awareness of what was going on,” Dr. Soto said. “Talking to each other about cases, and testing operations — that doesn’t happen automatically. Places have literally torn themselves apart fighting about masks and things like that. And the fact that they did not do it here is the real story.” Ms. Lent pointed to other subtle underlying factors. She said Dukes County has low rates of obesity and heart disease compared to other places in the country — both important factors for the rate of Covid-19 morbidity. More importantly, she said the Island has had a surprisingly small proportion of elderly people test positive for the virus, especially considering the Island’s demographics. While 17 per cent of the Island is 70 or older, only three per cent, or 49 of the 1,473 positive cases on the Vineyard, have been among the most high-risk age group. “Older people have taken it seriously and have clearly protected themselves through their conduct over the months like January, March and April where we had real transmission,” Ms. Lent said. “That demographic has not entered into the Covid picture in any significant way.” Nevertheless, the Vineyard has faced its share of challenges over the past 15 months. While the Island almost inexplicably saw no Covid spread during the summer, when the population ballooned, cases have spiked at least three times since the fall, with community spread still prevalent among year-round populations. Ms. Lent and Edgartown health agent Matt Poole said multiple residents became very sick from the virus — and both extended sympathies to people on the mainland who had lost loved ones to Covid-19.

“This is not something that should be taken for granted,” Ms. Lent said. “There are a number of cases I can point to that could have been losses.”

Dr. Stoto explained the seeming incongruity in summer versus winter cases by noting that almost all summer cases were connected to off-Island travel. When temperatures dropped and people spent more time indoors, the virus began to spread among the year-round community. The Island is also far from homogeneous, he said, with certain subgroups hit particularly hard, including tradespeople, immigrant communities and young people that work and live in large groups, while others remained far less touched.

Viral spread among young people also meant an increase in asymptomatic spread, and variants that infected entire households.

“All of those things came together,” Dr. Stoto said. “Despite that, I still think we managed to get a reasonable balance [of public health measures] right . . . We had to do them. If we had had the Ag Fair, how different would it have been from Sturgis? . . . And we could have done more, but it wouldn’t have been that much more effective. It would have been far more devastating in terms of the economy.”

As the Island vaccination rate continues to climb over 80 per cent and Islanders look to the summer, Dr. Stoto and Ms. Lent advised a healthy dose of caution. While a 90 per cent Island vaccination rate will protect most Vineyarders, there are still subgroups in which the rate will be much lower.

“The more people we have vaccinated the better off we are, but herd immunity is not a magic curtain,” Dr. Stoto said.

He was also quick to note that outdoor spread was never a serious risk, and that normalcy remains on the horizon. “Between vaccinations and reasonable things, like wearing masks indoors in shops, people will be able to enjoy a reasonable proximity of a Vineyard summer,” he predicted.

But Dr. Stoto — whose career is grounded in quantitative analysis — felt compelled to move beyond the numbers, pointing to a more intangible asset when explaining the Island’s ability to effectively fight the virus. It isn’t s

heer luck, he said, but something more intangible.

“It doesn’t happen naturally that everybody comes together and makes a shared sacrifice,” he said. “I call it the Island spirit . . . We found solidarity here. And I think that goes back to the sheer love that people have for this Island.”