The highly transmissible delta variant of the coronavirus is spreading like wildfire throughout the US, raising further concern for areas with low vaccination rates and renewing scrutiny of federal mask guidance.

The delta variant, first identified in India, now makes up more than 20 percent of cases in the US, with some estimates rising to at least 37 percent in recent days. The variant is rapidly overtaking the previously predominant variant in the US, Alpha, which was first identified in the UK and dominated the US in a matter of months this past spring. Scientists estimate that the alpha variant is around 50 percent more contagious than the original SARS-CoV-2 virus that exploded out of Wuhan, China.

Delta, on the other hand, is estimated to be 50 percent to 60 percent more contagious than Alpha. That is, it may be more than twice as contagious as the original virus.

COVID-19 vaccines are, fortunately, still effective against the delta variant, but many experts are extremely anxious about the risk the variant poses to areas with low vaccination rates. Already, some of the states with low vaccination rates and high transmission rates are seeing cases of delta take off.

Nevada and Missouri, for instance, have the nation’s highest rate of new cases per day (15 and 13.8 new cases per day per 100,000 people, respectively) and relatively low vaccination rates, with around 40 percent of their populations fully vaccinated. Both states have some of the highest estimates for delta’s prevalence, with current estimates around 70 percent—though the numbers are still shaky given data limitations.

In an interview with CNN Tuesday, top infectious disease expert Anthony Fauci laid out the concern, saying: “When you have such a low level of vaccination superimposed upon a variant that has a high degree of efficiency of spread, what you are going to see among undervaccinated regions—be that states, cities or counties—you’re going to see these individual types of blips. It’s almost like it’s going to be two Americas.”

Dr. Fauci previously called delta “the greatest threat in the US to our attempt to eliminate COVID-19.”

Guidance rift

But the unvaccinated aren’t the only people threatened by delta’s frenetic spread. Some experts point out that, although vaccines are still highly effective at preventing death and disease, they’re not 100 percent effective overall. There’s still a small chance that fully vaccinated people can get infected, and—although any such infections would very likely be asymptomatic or cause only mild disease—those fully vaccinated people could still help the highly contagious variant spread onward.

This is creating a rift among experts on what precautions fully vaccinated people should take. Those at the US Centers for Disease Control and Prevention argue that the risk of spread—to and from—fully vaccinated people is very low. As such, the agency continues to say that fully vaccinated people can shed their masks and walk among crowds. Other experts, including experts at the World Health Organization, are more precautious.

“We still live in a world that is only partially vaccinated, that has a lot of susceptibility, a lot of vulnerability,” Bruce Aylward, a senior advisor for the World Health Organization’s director-general, said in a press briefing last week. “So, what we’re saying is: once you’ve been fully vaccinated, continue to play it safe, because you could end up as part of a transmission chain.”

Aylward and several other WHO experts reiterated their long-standing position that everyone—even those fully vaccinated—should continue to do everything they can to reduce transmission, particularly as the delta variant spreads.

“The delta variant is a dangerous virus,” WHO’s technical lead on COVID-19, Maria Van Kerkhove, said in the briefing. “It is more transmissible than the alpha variant, which was extremely transmissible across Europe, across any country that it entered. The delta variant is even more transmissible… We are seeing trajectories of incidence that are almost vertical in a number of countries around the world.” Van Kerkhove encouraged people to continue to use masks consistently, stay in ventilated spaces, practice good hand hygiene and respiratory etiquette, continue to physical distance, and avoid crowds. “Please, do what you can to keep yourself safe,” she said.

“Maximum protection”

Mariângela Simão, WHO’s Assistant Director-General of Access to Medicines and Health Products, further emphasized the point, saying: “This is super-important: vaccine alone won’t stop the community transmission and we need to ensure that people follow the public health measures that Dr. Maria Van Kerkhove was speaking [of] today.”

The re-emphasis on distancing and masks for fully vaccinated people freshens scrutiny of the CDC’s stance, which was abruptly changed in mid-May. The agency announced with little warning that fully vaccinated people can largely stop distancing and shed their masks in nearly all indoor and outdoor settings, crowded or uncrowded. Exceptions include healthcare settings and mass transit.

Experts were quick to criticize the timing and manner of the announcement, saying the agency should have provided more warning to state and local health officials, as well as offer more nuanced recommendations for mask use in different settings, such as retail stores. And some experts at the time argued that the CDC should have offered thresholds. That is, they should have suggested cutoffs for when local vaccination levels are high enough and/or when transmission rates are low enough that it’s deemed safe to step down health measures.

As The New York Times, notes, Saskatchewan, Canada, has such thresholds, with phased reopening linked to vaccination rates. That “makes a lot more sense than just saying, ‘If you’re fully vaccinated, go ahead and take off your mask,'” virologist Angela Rasmussen told the outlet.

Though the CDC hasn’t made any movement on its guidance, health officials in other countries and local US officials have begun reinstating masking and other measures. For instance, Israel, one of the most highly vaccinated countries in the world, reinstated an indoor mask mandate this week. And on Monday, Los Angeles County Department of Public Health urged people to mask up in indoor settings, regardless of vaccination status.

“Until we better understand how and to who the delta variant is spreading, everyone should focus on maximum protection with minimum interruption to routine as all businesses operate without other restrictions, like physical distancing and capacity limits,” the department wrote in a statement.

https://arstechnica.com/?p=1777452