Some people don't get COVID despite being exposed to the virus — a mystery researchers are trying to unravel. Why it matters: Understanding the small cohort of "never COVID" people could lead to new vaccine targets or other protections as the world enters the third year of the pandemic. Various possibilities for how these people are protected are being tested: immune defenses stemming from other infections, human genetics, viral load or environmental factors. And then there's simple luck. The idea of resistant people may be "very intriguing," but "we don't know very often why someone did or did not get infected in sufficient detail to nail it," John Brooks, chief medical officer for the CDC’s COVID-19 Response Team, tells Axios.
Driving the news: Using a highly debated method called a human challenge study, a British trial deliberately exposed people who were unvaccinated and had no evidence of prior infection by placing a droplet of SARS-CoV-2 in their nose. They found 16 out of 34 participants did not get infected, according to the pre-print paper posted recently.
The latest: Researchers are now trying to zero in on that question. 1. Cross-immunity from the four endemic human coronaviruses is one hypothesis. Those other coronaviruses cause many of the colds people catch and could prime B-cell and T-cell response to this new coronavirus in some people. There's no compelling evidence one way or the other yet, Brooks says. But, infectious diseases often prompt some longer-term immune memory that can provide some assistance, he adds. It's also possible people didn't realize they had a prior asymptomatic COVID infection and gained enough immune cell memory to offer some protection.
2. Multiple genetic variations may make someone's immune system more or less susceptible to the virus. "I think there's probably something approaching 20 different genes already described that affect the likelihood of developing severe infection," Openshaw says. A genetic predisposition to not getting infected "is seen in other diseases where people have one or multiple factors that interfere with the virus binding to cells or being transported within," says Gigi Gronvall, an immunologist and senior scholar at the Johns Hopkins Center for Health Security. This rapidly evolving field offers promising research but "really isn't ready for prime time yet," Brooks says.
3. Mucosal immunity may play an underrecognized role in mounting a defense. 4. Where the virus settled on the human body, how large the particle was, the amount and length of exposure, how good the ventilation was and other environmental circumstances may also play a role, Openshaw says. https://www.yahoo.com/news/unlocking-mystery-never-covid-cohort-201849942.html - https://www.yahoo.com/news/unlocking-mystery-never-covid-cohort-201849942.html Safety, tolerability and viral kinetics during SARS-CoV-2 human challenge To establish a novel SARS-CoV-2 human challenge model, 36 volunteers aged 18-29 years without evidence of previous infection or vaccination were inoculated with 10 TCID50 of a wild-type virus (SARS-CoV-2/human/GBR/484861/2020) intranasally. Two participants were excluded from per protocol analysis due to seroconversion between screening and inoculation. Eighteen (~53%) became infected, with viral load (VL) rising steeply and peaking at ~5 days post-inoculation. Virus was first detected in the throat but rose to significantly higher levels in the nose, peaking at ~8.87 log10 copies/ml (median, 95% CI [8.41,9.53). Viable virus was recoverable from the nose up to ~10 days post-inoculation, on average. There were no serious adverse events. Mild-to-moderate symptoms were reported by 16 (89%) infected individuals, beginning 2-4 days post-inoculation. Anosmia/dysosmia developed more gradually in 12 (67%) participants. No quantitative correlation was noted between VL and symptoms, with high VLs even in asymptomatic infection, followed by the development of serum spike-specific and neutralising antibodies. However, lateral flow results were strongly associated with viable virus and modelling showed that twice-weekly rapid tests could diagnose infection before 70-80% of viable virus had been generated. Thus, in this first SARS-CoV-2 human challenge study, no serious safety signals were detected and the detailed characteristics of early infection and their public health implications were shown. ClinicalTrials.gov identifier: NCT04865237. https://www.researchsquare.com/article/rs-1121993/v1 - https://www.researchsquare.com/article/rs-1121993/v1
------------- "Facts don't care about your feelings" I'M A UNVAXXED DEVIL so kiss my rebel ass.
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