2020 vs. 2021: These charts show the similarities in Massachusetts’ COVID-19 surges

Ryan Huddle

It’s kind of eerie, really, and the numbers seem hard to believe. But COVID-19 cases in Massachusetts have been surging upward at almost exactly the same pace as this time last year.

Experts say it’s a coincidence that the numbers are so similar, given the millions of vaccinated — and now boosted — residents in Massachusetts. But, there’s also much more to the story.

Taken as a whole and balancing the rapidly rising number of infections against, for example, the lower number of hospitalizations and deaths, the data paint a picture of progress against the pandemic, they say.

Granted, that progress is precarious. But the hope is that it will continue, while scientists race to assess the threat of the new Omicron variant.

The trendlines in COVID cases in 2020 and in 2021 in Massachusetts began looking remarkably similar in late October. In late November, after dipping in tandem around Thanksgiving, they began to mirror each other. As of Dec. 3, the seven-day average of daily coronavirus cases was 4,303, remarkably close to the seven-day average of 4,462 on Dec. 3, 2020, according to Department of Public Health data.

Dr. Shira Doron, an infectious disease physician who is the hospital epidemiologist at Tufts Medical Center, said cases are going up again this year because the coronavirus appears to be “settling into a seasonal pattern.”

Seasonality of viruses, however, is not well understood by scientists, she noted. Is the coronavirus on the rise because people are gathering indoors? Or is it due to how the virus responds to colder weather? Or, even because of winter’s effect on the body’s susceptibility to the virus itself?

It could well be “some difficult-to-understand combination of those things,” she said.

Why is the rise in cases almost exactly the same this December as in December 2020? Experts said it appeared to be a statistical fluke, with the forces driving higher caseloads — such as the high transmissibility of the Delta variant and the lowering of coronavirus restrictions — on one side, and the high level of vaccinations in Massachusetts on the other.

“Last year schools were mostly closed, elderly people were not visiting relatives, no one was vaccinated,” said Andrew Lover, an assistant professor of epidemiology in the School of Public Health and Health Sciences at UMass Amherst. This year, schools are open, “everyone is mixing a lot more,” and a relatively high number of people are vaccinated.

“It’s just kind of by chance those two things have balanced out,” he said.

Dr. Scott Dryden-Peterson, an infectious disease physician at Brigham and Women’s Hospital, said cool weather and Thanksgiving probably contributed to the similar pattern in cases, but it was “unexpected” that the numbers would match up so closely.

“The benefits of widespread vaccination are apparently being offset by the added risk of a more infectious virus and more time spent together without masks,” he said.

Matthew Fox, a professor of epidemiology and global health at Boston University School of Public Health, said, “To a certain extent, waves follow a very similar pattern,” but “my hunch is that it’s a bit of a coincidence for sure.”

Meanwhile, while hospitalizations are steadily rising, the numbers are lower than last year. The number of people hospitalized as of Dec. 7 was 1,115, compared with 1,413 on Dec. 7, 2020.

Doron said the lagging hospitalization numbers this year were a sign of the “decoupling” experts had hoped for between the number of COVID cases and the number of hospitalizations and deaths. Still, it was “not as much as we would like to see.”

Lover also feels the hospitalization numbers are disappointing, especially coming as hospital systems are grappling with crowded conditions and staffing shortages.

“Everyone was certainly hoping the hospitalizations would be much lower,” Lover said. “The same numbers we saw last year may be more serious this year in terms of hospital capacity.”

Fox suggested the hospitalization numbers may be less worrisome than they seem. It might be that people hospitalized during this surge are less likely to take a turn for the worse, he said, because they’re vaccinated or because they’re younger.

Doron said she thinks the hospitalization data may include a number of people who didn’t come to the hospital because they were sick from COVID-19, but came for some other reason. They discovered they had COVID-19 only when they were tested at the hospital.

As for deaths, the numbers have been well below levels at the same time last year, which experts said was a tribute to vaccinations.

The seven-day average of daily coronavirus deaths as of Dec. 3 was 18, while the number was 40 at the same point last year. The numbers have only recently ticked up from the low teens to the high teens.

“If you look at the ratio of hospitalizations to deaths, we’re in much better shape than we were a year ago, which is what we were hoping the vaccinations would do all along,” said Lover.

More than 4.9 million of the state’s 7 million residents have been fully vaccinated, and among them, more than 1.5 million have received booster shots to shore up their waning immunity.

“Certainly, that is our ultimate goal: to keep mortality to a minimum,” Lover said, though he also noted that COVID-19 can have serious long-term effects on people who survive it.

Doron said another factor in lower death rates is treatments available in the hospital, including oxygen, intubation, the steroid dexamethasone, and the antiviral remdesivir. “We’re definitely keeping people alive in the hospital and getting them out of the hospital more” than earlier in the pandemic, she said.

But Lover cautioned that the increase in the number of deaths was still worrisome.

For this story, the Globe looked at data on COVID-19 positive tests and deaths as of the day they occurred, rather than on the day they were reported, and excluded the most recent days since the data are incomplete for them. The reported death numbers, which the DPH releases daily, have been ticking up in recent days, including a single-day total of 51 on Tuesday.

“That’s definitely creeping up more than we had hoped,” Lover said.

He and others are worried coronavirus cases will continue to climb well into January. The hope is that hospitalizations and deaths continue to lag cases.

What happens if the Omicron variant spreads widely in the state remains a major question, experts said. Scientists are investigating whether Omicron might be more transmissible, cause more severe disease, or be more successful than Delta at evading the protection provided by vaccines and prior infections.

“Omicron is definitely a wild card right now,” said Lover. “It could fizzle out and just not be very competitive and just disappear. But all signs are that it will probably be the main virus circulating sometime this winter.”

He noted that there are some early indications that Omicron causes less severe disease. But if it doesn’t and it spreads widely, “we’re in for a really challenging winter,” Lover said.

Even if Omicron is not more severe, a more transmissible variant could cause a larger overall number of cases and further stress hospital systems, Fox said.

“We don’t know what’s going to happen with Omicron,” he said. “I’m hopeful and I continue to remain optimistic that we’re not looking at a more severe variant.”

Both the Delta surge and the threat posed by Omicron underline the need for people to get vaccinated; get booster shots; get tested, including by rapid, at-home tests; and take precautions such as masking in indoor public spaces, experts say.

“If we all collectively take moderate steps, we can potentially avoid the worst of it,” Fox said.