February 26, 2024

What Ms. Burkett and Ms. Miller experienced was not the norm. Many of the conditions that can increase a person’s risk for severe Covid – obesity, heart disease, diabetes, smoking – are heavily influenced by the environment and behavior, not just genetics. A person’s history of fighting off other coronaviruses such as those that lead to colds can also affect their likelihood of developing a serious case of Covid.

Some researchers have also suggested that the amount of coronavirus a person ingests could have an impact on the severity of the condition, a trend that has been documented in other infections.


Jan. 18, 2021, 8:28 ET

“It makes the difference if your immune system is actually able to suppress the infection or if it is much more difficult to fight it when all of your cells are infected at the same time,” said Juliet Morrison, a virologist at the University of California in Riverside.

Michael Russell, 29, wonders if he tracked down more of the virus in the days after meeting his family on July 4 than his twin brother Steven did this summer.

Both brothers began to develop symptoms shortly after the celebration ended, around the time Steven returned to his home in Arlington, Virginia. The virus saddled Steven with a sore throat and a headache – a “mild, cold-like” illness, he said.

A few days later, Michael, who lived at home with his parents, had much more severe symptoms: a sore throat, chills, shortness of breath and fatigue, which banished him to his bed for a whole day. About two weeks passed before he could smell or taste the cinnamon-dusted popcorn that he regularly consumes.

The twins’ parents also had bad Covid symptoms, so Michael had to isolate himself with two other infected adults. Sitting together in the same house could have exposed him to a larger dose of the virus, the brothers said. But they added, that’s just a guess.