With surges in Covid-19 cases driven by the Delta variant, most Americans are now being advised to wear masks indoors — regardless of vaccination — by the US Centers for Disease Control and Prevention.
Since CDC guidelines updated Tuesday, we have learned more about the science that motivated these changes, both from a leaked agency document and a study published Friday by the agency. The new research reinforces the ongoing need for everyone who can get vaccinated to get vaccinated. Here are five key takeaways: Delta is super transmissible We knew Delta was spreading fast. In the United States and around the world, it swiftly overtook another variant, Alpha, that was already more transmissible than earlier strains. New research from Helix, a company whose Covid-19 tests have helped track a number of variants, shows how quickly that happened: Alpha made up 67% of cases in mid-May. Ten weeks later, it was down to just 2.3% — replaced by Delta, estimated around 90% of cases. „It’s one of the most transmissible viruses we know about. Measles, chickenpox, this — they’re all up there,“ Walensky told CNN Thursday. In terms of how quickly they spread, early strains of the coronavirus were similar to the common cold, according to an internal CDC document. Left unchecked, an infected person may have transmitted the virus to two or three people, on average, early in the outbreak. But now, with Delta, that number could be five to nine. This may be partly explained by Delta’s ability to „replicate faster and lead to higher viral loads earlier in infection compared to other variants,“ according to the preprint study from Helix. The CDC document also notes that Delta is „likely more severe“ than what came before it. Breakthrough infections may be contagious, but spread is driven by the unvaccinated Prior to Delta, even if you developed a breakthrough infection, you’d likely have less virus in your airways. Thus, you might be less likely to infect someone else if you were vaccinated. Experts say that vaccination still makes it less likely that you’ll catch Covid-19 in the first place — but for those who do, new data suggests that Delta causes similar viral loads in both vaccinated and unvaccinated people. The data is based on an outbreak investigation in Massachusetts in which nearly three-quarters of infected people had been fully vaccinated. Of them,8 in 10 developed symptoms, but only a few were hospitalized and none died. „The idea that someone could still test positive and still develop enough virus in their nose and mouth to transmit is really what this data is showing,“ explains CNN’s Chief Medical Correspondent Dr.
