Illustration: Annelise Capossela/Axios

More young people are being infected with the coronavirus, and even though they're less likely to die from it, experts warn the virus' spread among young adults may further fuel outbreaks across the United States.

Why it matters: Some people in their 20s and 30s face serious health complications from COVID-19, and a surge in cases among young people gives the virus a bigger foothold, increasing the risk of infection for more vulnerable people.

  • "We may see a pattern of younger people being affected initially, but then, in a number of weeks from now, we’re going to see a more deadly pandemic spreading to elderly people," says Alison Galvani, an epidemiologist at Yale University.

People can transmit the virus without knowing they have it, and younger people, in particular, could be unknowingly spreading the disease.

  • A study in Italy, yet to be peer reviewed, found the probability of having symptoms increased with age and that among 20–39-year-olds only about 22% had a fever or respiratory symptoms (compared to about 35% of 60–79-year-olds).
  • About half of the clusters in a study in Japan were traced back to people ages 20–39 at karaoke bars, offices and restaurants — and 41% of them did not have symptoms at the time.
  • "Younger people are at lower risk for serious COVID outcomes but are disproportionately responsible for asymptomatic transmission," says Galvani, who published a study earlier this week that found the majority of COVID-19 transmission is from silent carriers who are pre-symptomatic or asymptomatic.

By the numbers: From Arizona to Allegheny County, Pa., young people increasingly account for COVID-19 cases.

  • In the county of Los Angeles, nearly 50% of cases are now in people under 40 (compared to about 30% in April), per the LA Times.
  • In Harris County, Texas, home to Houston, 43% of the 40,000 cases are in people ages 20–39, as of yesterday.
  • In Florida, the median age of confirmed cases is hovering in the mid- to late-30s, compared to age 65 in March.

And the proportion of young people hospitalized for COVID-19 has also grown.

  • 40% of hospitalizations for COVID-19 at the end of June were for people 18–49-years-old, compared to 26% at the end of March, according to the COVID-NET database of hospitalizations in 14 states that represent about 10% of the U.S. population.

Between the lines: Yes, young people are going to bars and parties — but also to work.

  • 42% of people ages 18–39 said they had socialized without social distancing compared to 26% of people over 40, in a survey last month from the Democracy Fund + UCLA Nationscape.
  • 64% of frontline workers (grocery store clerks, health care workers, delivery drivers and other essential workers) are under 50.
  • There's a need for better education so that young people choose to take steps to prevent infection, says Lauren Ancel Meyers, a mathematical epidemiologist at UT Austin.
  • "But it also might come down to policies or regulations that get employers to ensure they are providing a safe workplace or resources to protect 20, 30 and other age groups that are working for them."

Where it stands: Young people are still much less likely to be hospitalized or die from the virus than people older than 60.

  • Yes, but: They can and do get very sick with the disease — from dangerous blood clots in their lungs to inflammation of the heart, lungs and even brain.
  • And the long-term consequences are unknown.
  • The risk is higher for young people of color: For example, the majority of coronavirus hospitalizations among Latino/Hispanic Americans are in people ages 18–49, my Axios colleague Caitlin Owens reported.
"The death rate among the young is not zero, and it is particularly not zero for people who have at least one co-morbid condition. This is not a completely benign disease of the young."
— Joshua Schiffer, of the Fred Hutchinson Cancer Center

What to watch: "If hospitals are strained now dealing with younger cases, they are going to be all the more taxed when the age distribution of infections shifts to the elderly," Galvani says.

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