Long Island residents under age 30 represented the largest share of new coronavirus cases since June — more than 40% — as many young people attended more social events and let down their guard against the virus, according to county health officials and data.
In Suffolk, people under 30 accounted for 46.7% of coronavirus cases reported between June 20 and Sept. 21, county health department data shows. The average age of people who tested positive for the virus in September was 32, compared with 42 in June, the data shows.
In Nassau, people under 30 were responsible for 38.8% of new cases between May 29 and Sept. 21, according to the Nassau County health department.
Among all age groups the rate of new infections in Nassau and Suffolk is about 1%, officials said.
The data showing the rising number of cases among young people comes as many of them return to schools, universities and workplaces after shutdowns that began in the spring. Concerns about positive cases have led to some temporary school closures on Long Island and remote learning at many universities around the country.
The demographic shift in cases runs counter to hypotheses early in the pandemic that young people weren't as susceptible to infection as older people.
At the beginning of the outbreak in New York, 83% of COVID-19 deaths were among people over age 60, and 73% of hospitalized patients were more than 51 years old, according to state health department data released in April and May.
Daniel Griffin, infectious disease chief for ProHEALTH Care, a private health care provider, said young people likely had less exposure to the virus early in the pandemic because schools were closed, although that has changed as many have resumed socializing.
"Hopefully, now it’s clear younger individuals can get the virus and spread the virus," said Griffin, a physician.
"And when that happens, people who are at risk will get the virus and we’re going to see the consequences," Griffin said.
Publication of the Nassau and Suffolk case data, compiled by Newsday from public records from both county health departments, comes after a summer in which local officials tried to clamp down on large gatherings that drew complaints from the public.
Such events included a July 25 concert by the EDM duo the Chainsmokers in Water Mill and July 4th weekend parties on Fire Island.
But neither of those events led to confirmed virus cases, Suffolk County Health Commissioner Gregson Piggott said.
Nor did outdoor protests that drew thousands of people after the death of George Floyd on May 25 in Minneapolis, said Piggott, a physician.
"Everybody was looking for the big superspreader event, but that's not what played out," Piggott said.
Instead, most new coronavirus cases were traced to backyard barbecues and graduation parties with 20 people or fewer, he said. On average, four attendees of individual events tested positive afterward, Piggott said.
In Nassau, health officials linked transmission to large parties, outdoor and indoor, and travelers returning from areas with more cases, county spokeswoman Christine Geed said.
At events with family and friends, adherence to protective guidelines to wear masks and practice distancing often "deteriorated" as people felt safer together, said ProHEALTH urgent care chief Bonnie Simmons, a physician.
Photos on social media sometimes showed "50 children together cheek-to-cheek" without masks, Griffin said.
"They want to have fun and they're young, but it's still dangerous," Simmons said.
People under 30 account for only .4% of COVID-19 fatalities in New York, state data shows. While young people may be more likely to experience mild symptoms or be asymptomatic, COVID-19 can be dangerous for all age groups, health officials warned.
"It is pretty clear while young people are not immune to the disease, they have an easier time fighting it off," although "that’s not universal," said Dr. David Battinelli, Northwell Health's chief medical officer.
The fact that young people represent an increasing share of new coronavirus cases on Long Island has caused concern among local officials as students, teachers, professors and staff begin returning to schools and colleges.
Suffolk County Legis. William Spencer (D-Centerport) and Deputy Presiding Officer Kara Hahn (D-Setauket) said they expected to see an increase in cases from schools this fall, especially as students get used to being together again.
Hahn said parents may start allowing their kids to hang out with friends again because they see them during school anyway.
"It’s a domino effect on all the different things that start to open up as a result of schools opening up," Hahn said.
Battinelli said he was less concerned about kids returning to local schools while cases overall are low in the area. But sending students back to college with people from areas with higher infection rates is "riskier," he said.
Health officials urged people to limit the size of gatherings of younger people, ensure there is adult supervision for children and to follow other health guidelines, even with friends and family they see frequently.
"The issue is pretty clear and that is, if you don’t mask, maintain social distance and pay attention to careful hand hygiene, you're at risk," Battinelli said.
Suffolk cases by age between June 20 and Sep. 10, according to county health department data:
Total cases: 4,710
Under age 20: 882
Ages 20-29: 1,242
Ages 30-39: 610
Ages 40-49: 518
Ages 50-59: 703
Over 60: 766