Editor's Note: For the latest updates on the 2020 coronavirus outbreak, see our news coverage.

Feb. 26, 2020 -- Viruses can strike one group more severely than another. The 1918 flu, which claimed 50 million lives worldwide, particularly affected young adults. The Zika outbreak that raged through Brazil in 2015-2016 had an especially devastating effect on pregnant women, attacking the brains of the fetuses they carried.

COVID-19, the disease caused by the new coronavirus that originated in China, appears to get more dangerous with age, says Michael Mina, MD, PhD, an assistant professor of epidemiology at the Harvard T.H. Chan School of Public Health.

“There seems to be this threshold -- below [age] 35 we’re seeing practically zero [cases],” he says. “As people increase in age from their 40s to 80s, we’re seeing mortality increase.”

The virus, which erupted late last year, now counts more than 80,000 cases and 2,700 deaths, the majority of them in China.

A study published Monday in The Journal of the American Medical Associationthat examined the first 45,000 cases in China found that 80% of the reported cases appear to be mild. The other 20% of those diagnosed had moderate, severe, or critical symptoms, including a hard time breathing, pneumonia, and organ failure. About 2.3% of overall infections have been lethal. Severe acute respiratory syndrome (SARS), a similar virus that started in China in 2002, also hit people over 60 the hardest. More than 8,000 people contracted the virus over 8 months, nearly 10% of whom died.

With COVID-19, so far children ages 1-9 account for just 1% of all Chinese infections, and none of the deaths, according to the JAMA study. Another 1% were ages 10-19.

Of people in their 70s who got the virus, 8% died, the study found, along with nearly 15% of those 80 and older. “Someone in their 80s has a pretty high risk of not leaving the hospital” if treated for COVID-19, Mina says.

Early data suggested that men were more vulnerable, as they accounted for just more than half the cases, according to the Chinese Center for Disease Control and Prevention. Infected men died twice as often as infected women. Mina says men might account for more cases because they were tested more often, but the “evidence is not strong to make any good conclusions.”