Its easy to assume that if one spouse or partner gets COVID-19 , the other is all but fated to get it, too.

But thats not always true. While studies have shown that the transmission risk of COVID from an infected person to a household contact is common, the risk varies widely. A recent report from the Centers for Disease Control and Prevention showed secondary transmission among close household contacts was 53%. Thats a high rate of transmission, but it also means that almost half of household contacts did not get COVID-19.

Even if the couple is exposed to the same sick person, one might dodge the infection entirely, or may be completely asymptomatic . While health experts are still trying to figure out why some are more susceptible to the virus, there are a few common reasons for this difference in experience.

First, the viral load for exposure was likely higher for the person who is sick, compared to the person who is not, said William W. Li , a physician and disease researcher.

Viral load refers to the total amount of virus a person has in their body. In theory, the higher the viral load, the more infectious someone is likely to be.

Lets say a couple threw caution to the wind and went to a social gathering that was also attended by a COVID-positive person.

Even if a couple were in the same room with the person, their levels of exposure may differ. One partner may have chatted with the person without a mask for more than 15 minutes the CDCs definition of exposure while the other may have exchanged greetings and kept their distance for the rest of the night. One may have washed their hands thoroughly while the other didnt. One might have been wearing a mask, while the other pulled theirs down to talk.

Each of these independent variables determines the likelihood of developing COVID after exposure, Li said.

Secondly, the partners both may be infected by the virus, but one may have an easier time fighting it off thanks to their immune system.

In this case, the infected but asymptomatic partner may have a more highly powered immune system that is able to battle the virus at the front gate in the body, and keep viral levels low enough so there is not enough to make the person sick, Li said.