A family member tests positive for COVID-19. The rest of the household develops classic symptoms of infection, but several rounds of testing result in negative results. It's a scenario that's become more common, leaving people with questions about whether they actually have COVID-19 or are infected with another virus.
In a June 2 piece for The New York Times, science journalist Melinda Wenner Moyer interviewed experts in immunology, microbiology and virology after this situation happened in her family: Her daughter contracted COVID-19 and after seven consecutive days of testing, no one else in her household tested positive, despite developing telltale symptoms.
The short answer as to why no one tested positive despite very close contact is that vaccines are doing their job. Vaccines slow down the virus' ability to replicate, and the immune system "keeps the viral load below the level of detection," Juliet Morrison, PhD, a microbiologist at the University of California in Riverside, told the Times.
"It's possible, then, that my husband and son did catch COVID-19, but their vaccinated immune systems fended off the infection so well that they never had enough viral proteins in their nose or throat to test positive. And their continual negative tests probably meant that they were never that contagious," Ms. Moyer hypothesized, based on her conversations with experts.
Ms. Moyer also wondered what explained the moderate symptoms if the viral load was so low. Experts said even without much virus in the body, powerful symptoms can still surface because many are a result of the immune system's response to the virus, rather than the virus itself.
While her son and husband developed classic COVID-19 symptoms, Ms. Moyer herself never did. That could be because her immune system "fought off the incoming virus so quickly that I didn't even have a chance to feel sick," Dr. Morrison told her.
Still, these are just possibilities, and "there are so many open questions" regarding how COVID-19 affects an individual's body, Raul Andino, PhD, a virologist at the University of California in San Francisco, told Ms. Moyer. He and his colleagues are now researching cases in which they repeatedly test households after one person tests positive.
"What we see is exactly what you described — that some people in the household don't test positive," despite symptoms, Dr. Andino said.