By Bill Shields

BOSTON (CBS) — Why is it that when some healthy people get COVID-19, they end up in the hospital, while other healthy people feel absolutely no symptoms?

“We don’t really know,” said Dr. Helen Boucher of Tufts Medical Center, “Maybe there’s something in the immune system, there’s a difference we can’t identify.”

Scientists around the world are trying to figure it out and so is Bryan O’Neil, a healthy Cambridge firefighter who got the virus about three weeks ago but whose symptoms were very mild.

“I never had a fever, never had a cough,” he said. “Why are my symptoms so mild, and other people are dying for whatever reason. A different strain or antibodies?”

Dr. Boucher said the immune system is key to unlocking the mysteries of COVID-19.

“We’re very hopeful that by fall, when we see another wave of this, that we’ll have therapeutic options before a vaccine,” she said.

Bill Shields