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Why Some People Are Still Getting Sick–but Not with COVID

On September 18 Orianna Carvalho woke up at 3 A.M. with a sore throat and the sniffles. At first she thought her symptoms were caused by allergies. But as the minutes ticked by, she began to worry they were caused by COVID-19. The following morning, Carvalho got tested at the University of Rhode Island, where she is a first-year doctoral student. Over the next few hours she developed a fever, and the catastrophizing began in earnest. When Carvalho finally learned that the cause of her misery was not COVID but the common cold, she was relieved but also surprised. “I have been so careful—wearing a mask every time I go somewhere, keeping at least six feet away from other people, using hand sanitizer and washing my hands,” she says. “I don’t know how I got sick.”

Carvalho is not alone. Many Americans have been puzzled to find that their best efforts to avoid COVID-19 have not always protected them from less troubling infections such as colds, stomach bugs and strep throat. How have other pathogens slipped through our anti-COVID defenses? There are no clear-cut answers, but the work of infectious disease specialists, virologists and epidemiologists—much of it conducted decades before the current pandemic—provides some clues. Their research shows that many microbes are more numerous, hardy and contagious than SARS-CoV-2, the virus that causes COVID-19. And for many of us, even our best efforts are not good enough.

The public health measures taken to stem the spread of SARS-CoV-2, which has been responsible for the deaths of more than 207,000 people in the U.S. to date, have also affected the prevalence of other respiratory viruses. This year the Southern Hemisphere essentially skipped flu season, which typically hits countries such as Australia, Chile and South Africa in May or June. Data from Australia suggest that although pandemic restrictions pushed many non-flu viruses out of circulation, a group of cold-causing pathogens known as rhinoviruses stuck around. A similar trend could be in store for the U.S., according to researchers who are tracking transmission of respiratory viruses in New York State, Washington State and Texas. Pedro Piedra, a pediatric infectious disease specialist at Baylor College of Medicine, says that although he has seen a significant decrease in many common respiratory viruses during the pandemic, he has noticed an uptick in rhinoviruses this fall.

Some virologists believe that the sheer number of viruses that cause the common cold can make it exceedingly difficult to avoid catching one: there are around 200 different pathogens. These include four coronaviruses (the group that includes SARS-CoV-2); four parainfluenza viruses (which, despite their name, bear no relation to influenza viruses); respiratory syncytial virus; and 160 different rhinoviruses. Viral censuses have revealed that dozens of these rhinoviruses circulate in any one place at a given time. “You might be immune to the flu, but you are not going to be immune to all those rhinoviruses,” says James Gern, a rhinovirus researcher at the University of Wisconsin–Madison. “That’s one unique feature of