| Deliberately infecting healthy young adults with SARS-CoV-2 sounded like a risky proposition when researchers in the UK began their so-called human challenge study in early 2021, a bid to better understand how the virus affects people. The controversial probe, however, has revealed unique and fascinating insights into the pandemic pathogen. This includes the identification of "super spreaders," how the nose is a key portal for transmission, and why some people — including Covid-19 super-dodgers or "Novids" — manage to boot the virus out of their bodies before it can ever cause illness. In the latest research, 16 volunteers who hadn't been previously had Covid-19 or even vaccinated against it were nasally administered a low dose of a pre-Alpha SARS-CoV-2 strain in a London hospital. Scientists then studied each participant, all of whom were 18 to 30 years old, for up to four weeks. Only six of the 16 had a sustained infection. Three were infected intermittently, and seven never tested positive at all because their immune systems rapidly eliminated the virus. By studying the respiratory and immune cells of each participant at specific time points, researchers could view different reactions to the virus in slow motion, unraveling key features associated with either susceptibility or resistance to Covid. One finding was that transiently-infected participants activated a swift antiviral mechanism in the mucosal tissue lining the nose, producing an immune signaling protein called type I interferon a day after infection. Interferon helps orchestrate the body's defense against viral pathogens and can be infused to treat conditions such as infectious hepatitis. In participants who had a sustained infection, type I interferon took five days to kick in, indicating a sluggish immune reaction at the precise location where the coronavirus likes to invade and replicate in a human host. The discovery fits with patterns of immune impairment that doctors linked to severe Covid cases months into the pandemic. And it supports research published in April that found the generic and widely available ointment Neosporin applied inside the nostrils could stimulate an interferon response to shield against SARS-CoV-2, flu and other airborne viral invaders. Akiko Iwasaki, a professor of immunobiology at the Yale School of Medicine, and her colleagues say this simple strategy could potentially be deployed in resource-limited countries to combat respiratory viral diseases. "This is an exciting finding, that a cheap over-the-counter antibiotic ointment can stimulate the human body to activate an antiviral response," she said. —Jason Gale | 
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