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Significance of spike in percentage of region's breakthrough cases unclear

As the number of coronavirus cases in the region has grown the last couple of months, the percentage of the hospitalized who have been fully vaccinated against the virus has climbed, too.

But that increase may not be as worrisome as numbers reported this week suggest. It may be as much about the math as the medicine.

During a news briefing Tuesday, Yale New Haven Health officials reported that 37 of the 137 COVID-19 patients being treated in the system’s five hospitals, including Lawrence + Memorial Hospital in New London and Westerly Hospital, had been fully vaccinated. At 27%, that was a markedly higher percentage of so-called breakthrough cases than some expected.

On Thursday, the system had 142 COVID-19 patients, 45 of whom were fully vaccinated — nearly a third. At L+M, four of 13 patients were vaccinated and at Westerly, four of eight were vaccinated.

Hartford HealthCare, which includes Backus Hospital in Norwich, reported a similar percentage of breakthroughs.

“About 25 to 30 percent of patients hospitalized with COVID-19 have been vaccinated,” Dr. Ajay Kumar, the seven-hospital system’s chief clinical officer, said Thursday. “These tend to be older and immunocompromised individuals.”

Kumar said at Backus, which had 21 COVID-19 patients, the percentage vaccinated was consistent with the health system as a whole.

“We can be looking at numbers that are not statistically significant,” Dr. Oliver Mayorga, L+M’s chief medical officer, cautioned. “We’d want to have a much larger data set before we make any assumptions.”

Still, small samples can fuel speculation.

“We knew you can still contract COVID despite being fully vaccinated, and we knew from the start it could be as much as 20% or even 30%,” Mayorga said. “When we see this difference in the proportion (of the vaccinated) who are getting the disease, we can assume it has something to do with delta.”

Delta, the coronavirus variant that’s now accounting for virtually all cases of the disease, is more contagious and virulent than other variants. While some of the vaccinated who contracted the virus remained asymptomatic, those exposed to the delta variant may be more likely to become sick enough to require hospitalization.

Another possible explanation for the increase in breakthroughs is that the effect of the vaccines wanes over time.

“For those vaccinated in January, there perhaps is an increased risk (of catching COVID-19)," Mayorga said. “That’s why the talk of boosters.”

Dr. Richard Martinello, an infectious-disease expert at the Yale School of Medicine, said the U.S. Centers for Disease Control and Prevention initially reported the COVID-19 vaccines’ effectiveness was in the 90% range. He said new research suggests the rate may be substantially lower.

Martinello said he expects the CDC to go forward with a booster program, probably by following the strategy it advocated in rolling out the vaccine. Health care workers, the elderly and those at greatest risk of become seriously ill or dying of COVID-19 could be the first eligible for a third dose.

The Wall Street Journal reported this week that federal regulators are likely to approve booster shots for vaccinated adults starting at least six months after their previous dose. Previously, the plan had been to begin boosters after a gap of at least eight months. 

Connecticut data

The Connecticut Department of Public Health reported that as of Wednesday, 7,121 cases of the coronavirus have been identified among fully vaccinated people in the state. Of the more than 2.2 million people who have been fully vaccinated, less than 0.32% have contracted the virus.

Fifty-three deaths linked to COVID-19 have occurred among the fully vaccinated, representing 5.8% of all COVID-19 deaths since Feb. 9, 2021.

The department reported that the unvaccinated, compared to the vaccinated, face five times the risk of contracting the virus; five times the risk of dying of COVID-19; and 16 times the risk of being hospitalized with COVID-19.

Gov. Ned Lamont’s office reported Thursday that 788 new COVID-19 cases were detected in the state since the previous day, and that 21,649 new test results were collected, a one-day positivity rate of 3.64%. Hospitalizations increased by two to 380.

Twenty-five more deaths had been linked to the disease since the previous Thursday, pushing the state’s toll since the pandemic began in March 2020 to 8,355.

b.hallenbeck@theday.com

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