In-Depth: Why can some people dodge COVID when others in their household fall ill?

Posted at 5:00 PM, Feb 08, 2022
and last updated 2022-02-14 16:59:10-05

SAN DIEGO (KGTV) – Scientists are unraveling some of the mysteries into why some people unexpectedly dodge COVID while others around them fall ill.

It happened to Carl Goldman and his wife Jeri back in January 2020. They were on the Diamond Princess cruise ship, the site of the first large COVID-19 outbreak outside of China, when Carl became sick.

He spent nearly a month in the hospital, chronicling his experience in a series of blogs. Jeri repeatedly tested negative, even though she was also exposed to several other infected passengers.

“It’s totally weird. I don’t know how she didn’t get it,” Carl said in an interview in 2020. When reached by phone this week, he said Jeri continues to test negative to this day.

Jeri and Carl Goldman are what scientists call a discordant couple: when two people share extended close contact but only one falls ill.

“Understanding why someone doesn't get infected or doesn't get sick is ultimately powerful,” said Dr. Alessandro Sette, a professor at the La Jolla Institute for Immunology.

Dr. Sette’s team is collecting blood samples from discordant couples to identify the mechanisms of this resistance.

This approach has been successful in the development of treatments for HIV. By studying long-term nonprogressors, the small group of people whose bodies can keep HIV under control without drugs, scientists were able to develop a class of HIV-blocking therapies called CCR5 antagonists.

There are several theories about the mechanisms underlying discordant couples, but the most active areas of research involve genetics and pre-exposure to another virus.

Last month, the journal Nature published a study that examined 52 household contacts in the U.K. The researchers found that people with high levels of pre-existing immune cells, called T cells, were less likely to get infected after an exposure.

These T cells are generated by the body after infections with other coronaviruses like the ones that cause the common cold.

The strength of the protection appears modest. The study found having these pre-existing T cells reduced the risk of infection by 6 percent, but research by Dr. Sette’s team shows these cells have a secondary benefit on vaccination.

“People that had this pre-existing T cell reactivity reacted faster and better to vaccination,” he said.

Other researchers have identified certain genes that may be protective against COVID, like the gene responsible for Type O blood. The effect is also small: the risk of infection dropped 12 percent in one study.

“It's quite possible it's going to be a mixed bag with more than one thing that is contributing to this phenomenon,” Dr. Sette said.

There are other potential explanations for a discordant couple. It might be the result of vaccine timing and the effects of waning immunity. If one person was vaccinated more recently than another, the former might have slightly more protection, Sette said.

Another theory has to do with asymptomatic infection. Perhaps one person was infected several weeks before their partner and didn’t know it, allowing them to build direct immunity against the virus.

Finding a way to leverage the immune cells or genes that drive natural resistance could help scientists develop a pan-coronavirus vaccine or other treatments, Dr. Sette said.

“That could be a broad-spectrum anti-coronavirus weapon,” he said.