Health Care

Limited breakthrough stats show heightened threat of Delta variant

Throughout the recent surge in Covid-19 cases, health officials have worked to make two points clear: The available vaccines are extremely effective at preventing severe illness from the coronavirus, and the more contagious Delta variant merits caution.

New data from the Vermont Department of Health drives both points home.

Cases have appeared in just 0.14% of the vaccinated population, one indicator of the overall effectiveness of vaccination. But that rate has dramatically increased as the Delta variant has spread.

According to past health department reports, the share of vaccinated Vermonters with “breakthrough infections” hovered at 0.06% throughout the spring and early summer, when the Alpha (B.1.1.7) variant was dominant. In a report on July 30, that rate increased to 0.08%. 

As of Friday, the rate has risen to 0.14% — more than twice the rate reported a month ago. 

The hospitalization rate among vaccinated Vermonters appears to be rising as well, but experts warn that those numbers are still too small to draw clear conclusions. 

As of Friday, six of the 23 people reported hospitalized in Vermont were fully vaccinated, including four who were in intensive care, according to health department spokesperson Ben Truman.

Truman stressed the small overall percentage of breakthrough cases, adding that instances of vaccinated people being hospitalized due to Covid-19 “tend to happen in people with underlying conditions.” Vaccinated Vermonters are statistically more likely to be older and therefore more likely to have other health issues.

Unvaccinated people remain at the highest risk of catching and spreading the coronavirus, data shows. According to the health department’s latest report, unvaccinated Vermonters have this year accounted for: 

  • 98% of all Covid-19 cases
  • 93% of deaths
  • 96% of hospitalizations

Recent multi-state analyses have emphasized the low overall rates of infections and hospitalizations among vaccinated people. But some experts this week have argued that those statistics, dating back to January, may undersell the more recent elevated risks from the Delta variant.

According to CDC estimates, Delta became the dominant strain in the northeastern U.S. around the middle of July. Genome sequencing data from the Vermont Department of Health showed Delta becoming dominant in the state in the weeks leading up to July 20.

More recent data is critical for understanding how Delta behaves differently from previous strains, according to experts surveyed by The Atlantic. Though breakthrough cases are still rare, the rising rate bolsters the argument that a layered approach to mitigation — including robust masking guidance — may be needed to supplement the protection offered by vaccines.

Fully vaccinated people with breakthrough infections can now also contribute to spreading the virus, according to the CDC. Recent studies show that, unlike previous variants, Delta produces the same amount of virus in infected people whether they are vaccinated or unvaccinated.

However, vaccination appears to suppress the virus more quickly, making vaccinated people contagious for less time, the CDC said. Plus, experts note, vaccinated people remain far less likely to get infected in the first place, diminishing their overall contribution to community spread.

Cases and outbreaks on the rise

Mark Levine. Photo by Mike Dougherty/VTDigger

The health department snapshot, published every other week, is the only data the state makes regularly available about the vaccination status of new cases. (Limited numbers are also provided at Gov. Phil Scott’s weekly press conference.)

Health Commissioner Mark Levine said Tuesday that the recent focus on breakthrough cases is misplaced. He suggested that some are mistakenly interpreting those numbers as evidence that the vaccines are less effective than previously thought. 

“If you look at news of the so-called breakthrough cases as a reason to not get vaccinated, take my reassurance that this is completely unjustified,” Levine said. 

Some misinterpretation of breakthrough data may be due to the ever-expanding population of vaccinated people. As a larger percentage of the state becomes fully vaccinated, a larger percentage of new cases will necessarily crop up among fully vaccinated people. (Experts say to imagine that Vermont had a 100% vaccination rate, in which case every new infection would then be considered a breakthrough.)

The number of breakthrough cases is also bound to rise as overall cases continue to spike. Vermont reported 166 new cases Thursday, the highest one-day total so far in the latest surge of the pandemic. State officials expect cases to remain elevated through mid-September, according to modeling data presented earlier this week.

The health department data summary also provides a glimpse at the rising number of outbreaks in Vermont. There are 19 active outbreaks, up from eight in the reporting period ending July 30.

New cases associated with outbreaks were reported in four types of settings:

  • Congregate care: 14 new among residents, four new among staff
  • Health care: five new
  • Schools and child care: 41 new among children and staff
  • Workplaces or businesses: 45 new

Levine said Tuesday that most current outbreaks are small, thanks to widespread vaccination, and they’re occurring in the same types of settings as in previous stages of the pandemic. 

As of Friday, 84.6% of Vermonters age 12 and over have gotten at least one dose of the Covid-19 vaccine.

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Mike Dougherty

About Mike

Mike Dougherty is VTDigger’s digital editor. He is a DC-area native and studied journalism and music at New York University. Prior to joining VTDigger, Mike spent two years as a program coordinator for the Vermont Humanities Council. Before moving to Vermont in 2015, he spent seven years managing recording operations for the oral history nonprofit StoryCorps, assisted Magnum photographer Susan Meiselas, and contributed to the Brooklyn-based alt-weekly L Magazine.

Email: [email protected]

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