Will the BA.5 COVID strain force new mask mandates?

The new COVID-19 variant, called BA.5, has been rapidly spreading across the country and is now estimated to make up more than 60% of new cases, according to the CDC. It is highly transmissible, compared to previous variants, and seemingly more resistant to prior vaccinations and immunities.

These factors are making people think differently about wearing masks, which experts say are still an effective way to curb the spread of the virus. Los Angeles County, for example, will likely reinstate an indoor mask mandate at the end of the month due to rising COVID-19 cases.

ABC News’ “Start Here” podcast spoke on Monday with John Brownstein, Chief Innovation Officer at Boston's Children's Hospital, professor at Harvard Medical School and ABC News Medical contributor, about best practices for protecting people against this latest variant.

START HERE: John, the mask debate has been with us as long as COVID. Los Angeles County is talking about reinstating mask rules. How effective are masks against this super contagious subvariant BA.5?

BROWNSTEIN: You know, Michelle, there is nothing as contentious as the mask debate of anything that we've dealt with with the pandemic. And it's very surprising as a scientist, because a layer between you and others that protects you from transmission, it seems like very basic science.

But also at the community level, when you take on masks at the community level, you will see transmission go down. And that is why communities like L.A. are deciding to take on masking, because they're looking at their particular context, seeing a surge and ultimately applying correct interventions to help reduce risk and ultimately not allowing for further transmission. That would ultimately create a surge in our hospitals and a capacity concern.

And so masking makes sense, but in a highly targeted way. That's why we have to be very specific in the timing of masking. You're pre-surge in the community. You're seeing cases go up. That's when you want to bring in masks to help reduce transmission, help reduce the risk to our health systems.

But these are not broad scale mask mandates across the country for undefined amounts of time. These are very targeted and this is why it's done at the local public health level. They can look at the data and make these decisions and have people engage in a very important intervention to reduce the risk to the community.

START HERE: In terms of vaccination….we are in a much better place than last year. More Americans are vaccinated, boosted. There are treatments to help with symptoms. But how is this latest subvariant throwing a wrench into all the tools we have at our disposal?

BROWNSTEIN: Well, first, it's really important to note that the tools that we have still work. If you're fully up to date with your vaccines, especially if you're on that booster and that second booster, if eligible, it dramatically reduces your risk of severe illness and death. So that's point No. 1. Testing still works. Masking still works. So all the tools still work.

The issue is that this new variant is highly transmissible. It's immune evasive in the sense that if you are exposed to this variant, your previous immunity from vaccination and potentially other variants, likely non-human variants, doesn't necessarily protect you in the same way as previous infections. And so we're going to see increased amounts of breakthrough infections.

Many of those will not turn, of course, into severe illness, but they're turning into infections that ultimately lead to more transmission. And then we'll see the impact in our most vulnerable communities, those that are elderly, immunocompromised, and we'll see history repeating itself. And that's the real concern we have with this new immune evasive variant.

START HERE: And how does testing factor in -- should Americans be testing regularly at home?

BROWNSTEIN: Yeah, testing is such an important first line of defense. It's been the cornerstone of our response. We've seen testing dramatically reduce. People are not going to get PCRs and even home testing is declining.

And that's a problem because if people don't have awareness of their infection, they are not necessarily isolating and potentially creating risk into the community. And that leads, of course, to these surges that we're seeing. And so I advocate, you know, the testing. It's simple. You know, there's so much availability. There's free home tests that the Biden administration is offering. Please use those because that really will have such an impact on the course of this BA.5 surge.

START HERE: Health experts say they are focusing on a booster for adults this fall -- a new one targeting the latest subvariants? But should the government be expanding access to the second booster we have now for all adults?

BROWNSTEIN: Well, you know, it's a very complicated answer because the data isn't absolutely clear about this for young, healthy adults, for older Americans. Those compromised. The risk is significant and getting that second booster is clear. I think we're still waiting for compelling data at the same time. There should be broad availability. You know, there is plenty of supply out there. So if someone feels, based on their own risk tolerance, that they want that second booster, there's really no downside.

So it makes sense to expand that availability. But we have to be very careful here because the messaging on boosters has been complicated. We don't want to create vaccine fatigue, and we especially want to make sure that we have compelling reasons to get people boosters in the fall when we have this new variant specific bivalent vaccine. So I think making sure that we can make it available to as many people [who] will want it without sort of undermining a potential fall vaccination strategy.

START HERE: All right. That is John Brownstein with Boston Children’s Hospital. Thank you.

BROWNSTEIN: Thanks, Michelle.