Health Care

‘Breakthrough gap’ is narrowing, but don’t panic. Here’s what the data says.

Note: This story is more than a week old. Given how quickly the Covid-19 pandemic is evolving, we recommend that you read our latest coverage here.

Vermont has reported a steep rise in Covid-19 cases, nearly doubling from 90 weekly cases to 171 over the past week, according to a report Tuesday from the state Department of Financial Regulation.

It’s clear that Vermont has been affected by the recent rise in cases throughout the country, led by the spread of the Delta variant. 

“About five weeks ago, Covid-19 cases started to rise in the United States; about four weeks ago, cases started to rise here in the Northeast; and then about three weeks ago, they started to rise here in Vermont, reminding us, again, that Vermont is not an island,” said Mike Pieciak, commissioner of the state financial regulation department.

Vermont’s high vaccination rates — 83.6% of eligible Vermonters as of Tuesday — “have helped keep cases lower and have kept severe outcomes to a minimum,” Pieciak said. Vermont remains the best in the nation in terms of the percentage of the population that has received at least one dose of the vaccine. 

But headlines have recently emphasized the risk of the variant, even for vaccinated people. Some early research shows vaccines are less effective against the Delta variant than earlier versions of Covid-19, and vaccinated Vermonters that have become “breakthrough cases” — contracting the virus despite being fully vaccinated — have expressed concern that Vermont guidance doesn’t go far enough.

VTDigger reviewed Pieciak’s weekly report and Department of Health data to ask: Are breakthrough cases rising in Vermont? And is the gap between unvaccinated and vaccinated cases narrowing?

The answer to both questions is: Yes, but that doesn’t undermine the protective factor of vaccines. Even data from the most recent wave of the Delta variant shows that vaccinated Vermonters are at less risk of contracting the virus, and are probably at less risk of hospitalization and death, than unvaccinated people.

Data from July shows that the number of breakthrough cases per day ranged from zero to 10, with a single exception of 17 cases on July 21.

In comparison, cases per day among unvaccinated or partially vaccinated Vermonters increased from less than 10 a day early in July up to 10 to 20 per day in the past week. 

That’s true even though the pool has shrunk: Less than 17% of eligible Vermonters are not yet vaccinated. (A few cases were among out-of-state residents whose vaccine status could not be confirmed.)

The gap between vaccinated and unvaccinated Vermonters gets even wider when the size of both populations are taken into account. Fully vaccinated Vermonters were roughly two-thirds of the population in July, yet accounted for only 30% of reported cases. 

According to a chart from the Department of Financial Regulation, while the rate of cases among vaccinated Vermonters has risen in recent weeks, it’s still far below unvaccinated Vermonters. And both populations are far below Covid’s peak in April.

That may be why the gap between the unvaccinated and vaccinated population has narrowed. Last week, Mark Levine, the state health commissioner, said unvaccinated Vermonters were 12 times more likely to get Covid than vaccinated Vermonters, but so far in July, it’s more like three to four times more likely.

It’s worth noting that the lower overall number of cases in July, compared to April, means there’s a smaller sample size to compare rates. And Vermont, in itself, has smaller numbers compared to the rest of the nation. Research studies that look directly at a controlled sample of vaccine recipients are the most reliable way to determine the effectiveness of vaccines.

Although the state did not provide data this week on breakthrough hospitalizations and deaths, Isaac Dayno, a state spokesperson, said collection and analysis of that data was “in motion” and the results may be presented at the Covid press conference next week.

Pieciak said Tuesday that Vermont’s relatively low hospitalization rate and death rate are a sign that vaccines are preventing the worst outcomes of Covid.

Vermont currently has an average of three hospitalizations per day, and has reported one death so far in July.

“If someone decides not to be vaccinated, they are choosing not only to endanger themselves, but those who they live with, work with and socialize with, and ultimately are helping prolong the pandemic,” Pieciak said.

Correction: An earlier version of this story misstated the rise in Covid-19 cases over the past week.

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Erin Petenko

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