Jayson Molina Majano, 17, of Freeport, is administered a vaccine...

Jayson Molina Majano, 17, of Freeport, is administered a vaccine by nurse Tricia O'Brien on Thursday at Freeport High School. Credit: Newsday/Steve Pfost

People who are not vaccinated against the coronavirus are "at very high risk" of getting infected, experts say, as the highly contagious delta variant continues to cause a spike in COVID-19 cases.

In New York, the percentage of coronavirus tests coming back positive has tripled in just over three weeks, from 0.35% on June 23 to 1.09% on Thursday, and the number of cases increased from 343 to 981.

What to know

The number of COVID-19 cases continues to climb in New York as the highly contagious delta variant spreads. New York's seven-day positivity rate has more than tripled in the past three weeks.

Experts urged unvaccinated people to get inoculated. Until they do, they should wear masks, practice social distancing and avoid crowds, especially indoors.

Vaccinated people face far less risk. They’re less likely to get infected and, even if they do, the vaccines offer almost complete protection against severe illness or death, experts say.

"What we know for sure about the delta variant is it is highly transmissible, which means someone who is unvaccinated is at very high risk, is extremely vulnerable, if they come in contact with someone with delta," said Dr. Wafaa El-Sadr, a professor of epidemiology and medicine at the Mailman School of Public Health at Columbia University.

Dr. Bettina Fries, chief of infectious diseases at Stony Brook Medicine, said that when she visits hospital patients, she is "really astonished how many people are not vaccinated. People for whom it doesn’t make any sense: They’re obese, they have underlying disease, they have every risk factor."

Fries said her first advice to unvaccinated people is to get the shot. For those who don’t, they must take precautions such as wearing a mask and practicing social distancing, she said. The large number of unvaccinated people not wearing masks is a key reason the delta variant is spreading so quickly, she said.

"If you’re not vaccinated, you are really playing with fire if you don’t wear a mask right now," she said.

The worrisome numbers may underplay how widely the delta variant is spreading, because positive test results generally reflect the number of infections that were occurring about two weeks before, because of the incubation period of the virus and other factors, said Dr. Bruce Hirsch, an infectious disease specialist at North Shore University Hospital in Manhasset and Long Island Jewish Medical Center in New Hyde Park.

"We can’t really say what exactly is happening at this moment," he said.

The number of people hospitalized for COVID-19 statewide rose on Thursday by 20 patients, to 360. But hospitalizations have remained roughly level — between 330 and 370 — since June 26, state Health Department data shows.

Yet just as positive test results lag infections, hospitalizations lag test results by about two weeks, so the effect of the surge in cases is still unclear, Hirsch said.

Dr. Aaron Glatt, chairman of medicine and chief of infectious diseases at Mount Sinai South Nassau hospital in Oceanside, said hospitalizations likely won’t rise as sharply as new cases, because the people most vulnerable to severe illness or death — such as older adults — are more likely to be vaccinated than young people.

"We will probably see increases in hospitalizations, ICUs [intensive-care patients] and deaths, but probably not paralleling exactly the increases in cases, because more of these cases are in relatively healthy, younger people," he said.

In New York, 84% of those 65 to 74 are fully vaccinated, compared with only 48% of people 16 to 25, according to the state Health Department.

Doctor: Avoid large, indoor gatherings

Vaccinated people have much less to worry about than the unvaccinated, health officials say. More than 99% of COVID-19 deaths are in unvaccinated people, Dr. Anthony Fauci, chief medical adviser to President Joe Biden, said Sunday.

"The risk is not zero," El-Sadr said. "But what’s reassuring is this vaccine appears to protect against severe illness even with the delta variant, which means for an individual who is vaccinated, even if they get infected, they’re likely to not get very sick."

Even so, El-Sadr said, vaccinated people should consider avoiding large, indoor gatherings, and, if they’re indoors, to wear a mask, to reduce the risk further.

Los Angeles County officials Thursday announced that, because of rapidly increasing caseloads there, they would reinstitute indoor mask mandates for everyone, vaccinated and unvaccinated.

Hirsch said that, in New York, rates are not high enough yet to reimpose mask, capacity and other restrictions. But, he said, if the upward trend continues, "We’ll have to do the same thing we did last spring when the rates were very high — mask mandates, avoiding crowded indoor places."

In addition, he said, "I would hope there would be some way to check vaccine status. I would be much more comfortable going to a restaurant, a play or concert if there’s a vaccine requirement."

Fries predicted rates would indeed climb higher, especially in the fall, as cooler weather pushes more activities indoors. COVID-19 cases rose last autumn as well, but this year, with the lack of mask and other restrictions, and with many people returning to workplaces, universities and public transportation, "The virus will spread rapidly, faster than last year, because last year people were running around with a mask."

Fries said mutations like the delta variant develop because of the large number of unvaccinated people.

"If we want to break this vicious cycle, we all just need to step up to the plate and get vaccinated," she said. "You don’t only get vaccinated for your own safety. You get vaccinated to stop the pandemic. You get vaccinated so you don’t become a vehicle of this virus. Even if you don’t get sick, you don’t want to transmit it to anybody."

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