It’s been nearly three months since the first coronavirus variant case was confirmed in Massachusetts, and variants have been spreading insidiously through the state since.
The B.117 variant from Great Britain, which the US Centers for Disease Control and Prevention says is now the most common in the United States, has been detected in hundreds of Massachusetts samples. The P.1 variant that rampaged through Brazil was recently connected to a cluster of cases on Cape Cod. The B.1.351 variant that emerged in South Africa has also been found here.
The rise of the variants is troubling, epidemiologists say, given that they can be more infectious and more deadly. The variants are believed to be one of the possible reasons for a concerning uptick in the state’s coronavirus cases.
But how much exactly should we worry, given that so many in this state have already been vaccinated or are on the cusp of eligibility? The truth is, it’s hard to tell, even for the experts.
For now, the best we can do is assess the data we have on the variants. Here’s a quick look at some of what we know.
First, let’s look at the number of cases of coronavirus involving the variants in Massachusetts detected so far. The CDC and state say 977 cases of the British variant, 82 cases of the Brazilian variant, and 12 cases of the South African variant have been found. The numbers have been growing since the state’s first case, a British variant, was announced on Jan. 17.
The British variant totals are the fourth highest in the United States, while the Brazilian variant totals are the second highest.
Here’s a county-by-county map from the state Department of Public Health of where the cases have been found.
An important caveat: This data doesn’t represent the real number of variant cases. The genomic sequencing needed to look for variants is done only on a limited number of tests. The numbers are “based on a sampling of SARS-CoV-2-positive specimens and do not represent the total number of ... cases that may be circulating,” the CDC says.
Next, let’s look at the proportion of various variants in the state. Data from CDC suggests that the British variant, as of mid-March, was accounting for nearly a fifth of cases in the state, while two other official variants of concern, the B.1.427 and B.1.429, or California variants, are second most prevalent.
Again, the data from a limited number of tests comes with a caveat. The CDC notes, “Proportions of variants do not represent the total number that may be circulating.”
Data from a much different source provides another warning sign that variants are lurking in Massachusetts. The Massachusetts Water Resources Authority has found the British variant in the wastewater at the Deer Island treatment plant.
Biobot Analytics of Cambridge, the company that does the testing for the MWRA, says its testing has always been able to pick up coronaviruses, no matter what the variant. But recently, the company announced it has added the capability of specifically distinguishing when its sampling has picked up the British variant. The days that variant was detected are shown in green on the chart.
The focus on the British variant is understandable, given its predominance among the variants. It is also about 60 percent more contagious and 67 percent more deadly than the original form of the coronavirus, according to the most recent estimates.
On the national level, the CDC also reports the number of variant cases by state, broken down by the three best-known variants of concern.
The same caveats about limited testing apply.
Using data gleaned from genomic sequencing tests, scientists at Scripps Research Institute have calculated a national-level estimate of the proportion of coronavirus cases caused by variants of concern and variants of interest, a less worrisome category.
This chart suggests that variants of concern were involved in about a third of all current coronavirus cases nationally as of mid-March.
The CDC’s efforts to track the spread of coronavirus variants came under fire early this year. But they have substantially improved in recent weeks and are expected to continue to improve, in large part because of the $1.75 billion in funds for genomic sequencing in the stimulus package.
Still, the testing for the variants needs to be more systematic, more extensive, and more nuanced, said Dr. Thomas Tsai, an assistant professor at the Harvard T.H. Chan School of Public Health.
The general picture that emerges is clear, however. The British, South African, and Brazilian variants, are gaining ground in the United States, which underlines the need for people to continue taking precautions to prevent the spread, he said.
“The top-line message is fairly consistent. There’s a growing prevalence of the variants of concern. And that argues for continued vigilance over the next several weeks even as the vaccine rollout is proceeding ahead of schedule,” Tsai said. “We’ve come a long way, but we’re still not out of the woods.”
Amanda Kaufman of the Globe staff contributed to this report. Material from Globe wire services was used in this report.
Martin Finucane can be reached at firstname.lastname@example.org. Vince can be reached at email@example.com. Follow him on Twitter @vince_dixon_.