COVID-19 cases are on the rise nationally, and new, more contagious variants of the virus are beginning to make up a larger share of those cases. The variants have been found here in Massachusetts. GBH News' Craig LeMoult discussed what we know about their local presence with GBH All Things Considered host Arun Rath. This transcript has been edited for clarity.

Arun Rath: What variants have been detected in Massachusetts already? And do we know how prevalent they are?

Craig LeMoult: There are several different strains that have been found here. The one we're seeing the most of is called B.1.1.7. That's the variant that was first detected in the U.K. Right now, health officials are estimating that's making up between six and seven percent of the total cases in the state that we're seeing. The CDC is also reporting 58 cases of the P.1 variant. That's the one that comes from Brazil. There are also 12 cases of the South Africa variant as well. But especially in those cases, the actual number of those cases could be far higher, health officials say, based on our limited ability to detect them.

Rath: So how are we detecting them or estimating them?

LeMoult: When someone tests positive for COVID, they can't just tell right away which variant they have. It just says they got COVID. To understand which variant they have, you have to search for the changes in the genetic sequence of the virus, and that's a much more complicated test. The state is now working with the Broad Institute to do those genomic tests, but right now they're only able to check about one percent of all of the positive COVID tests in the state. That's apparently enough for them to make that estimate that right now, between six and seven percent of current cases are the B.1.1.7 variant. I talked with Dr. Bronwyn MacInnis. She's the director of Pathogen Genomics Surveillance at the Broad Institute, and she says they're scaling up their testing and hope to be able to do genomic sequencing on five percent of the positive tests by May.

"We are just beginning to get a sense of what's out there and how big of a threat this is," MacInnis said. "And that comes at a time when we know that these variants of concern are finding their way into our community and they very well may be creeping up. So we're finally able to see them at the most critical time."

Now, there is another way that scientists have confirmed the presence of the B.1.1.7 variant in Massachusetts. There's a company called Biobot that's been taking samples of wastewater to test for COVID, and they have started checking in that wastewater to see if the U.K. variant is in there. And sure enough, the wastewater in the towns that get their water from the MWRA, where the testing is happening, they started testing positive for the variant on and off over this past month.

Rath: We know these variants are in the state. Do we know where in the state they are, if they're concentrated in particular areas?

LeMoult: The MWRA wastewater doesn't let us zoom in to where the virus is. It just says it's there, we know it's present. We do know from genomic testing that an outbreak on the Cape, for example, in Barnstable County, is the P.1 variant, the Brazilian one. We also do have some information about the variants specifically in Chelsea. I spoke with Cris Alonso. She recently got her PhD from Harvard after doing her dissertation on COVID in Chelsea. She's now working with the Chelsea nonprofit La Colaborativa and with the Center for Complex Interventions. They have Biobot sampling wastewater specifically in Chelsea, in different spots around the city. She says they detected B.1.1.7 in four wastewater sites around Chelsea on March 23rd and then again on March 30th.

"What that tells us is that B.1.1.7 is present in Chelsea," Alonso said. "What that tells us is that it's going to continue to transmit throughout the Boston area and beyond. And what that tells us is that it's time to take prevention measures seriously before we can all get vaccinated."

Rath: You and I both know Chelsea has been hit pretty hard by the pandemic.

LeMoult: It really has, and that has these public health experts particularly concerned. Again, these B.1.1.7 strains are 50 percent more infectious than the old virus that we got to know. And Chelsea is a is a very densely populated city. Oftentimes, many people are living in homes together, multigenerational families. Many of the people in those homes are frontline workers. So there's a serious risk, especially in a community like Chelsea. Groups like La Colaborativa have been trying to get the message out in Chelsea to people that they need to be extra cautious, that this variant is in the community, and they're offering free COVID testing and really trying to reach out and make sure that people are aware of this. But it's important to stress —The risk is not just in places like Chelsea. I talked with Dr. Regina LaRocque. She's an infectious disease physician at Mass. General and an associate professor at Harvard Medical School.

"Those variants have an advantage," LaRocque said. "And so as long as the circumstances are such that there is viral transmission happening at relatively high rates like we have now in Massachusetts, those variants are going to become the predominant strains of the virus in Massachusetts."

Rath: The rise in these more contagious variants and the virus overall — I feel like I'm saying this every day this week — that rise is correlating with loosening restrictions in the state and the rolling back of restrictions. Today is opening day for the Red Sox, with fans in the stands.

LeMoult: Yeah, absolutely, and that is just a serious source of concern for all of the health experts that I spoke with. Gov. Charlie Baker was asked about the variants earlier this week when he did a press conference with the CDC director, Rochelle Walensky. She's been trying to raise the alarm about these new variants recently. Baker acknowledged it is an issue here in Massachusetts.

"That is very much present here, and it's very contagious," Baker said. "And it's why people can't let down their guard, even when they are in informal settings."

But a lot of the infectious disease experts and the public health experts I've been speaking with say, you know, it's not just about personal choice. They say, basically what we have right now is a race between vaccination and between these new variants, and it's going to take a while for enough people to be vaccinated. And not only does the relaxing of restrictions mean more people interacting with one another, they say it's also leading to a false sense of safety exactly as the virus becomes more contagious.