Connecticut has seen an “extremely concerning” rise in COVID-19 hospitalizations in recent weeks, health officials said, as the number of cases also continues to trend up.

The state health department reported at least 500 hospitalizations on both Monday and Tuesday, marking a roughly 80% increase in the past two weeks — and the highest numbers since April.

“To go from 300 hospitalizations to 500 hospitalizations in such a short period of time is extremely concerning,” Dr. Manisha Juthani, commissioner of the Connecticut Department of Public Health, told ABC New Haven affiliate WTNH Tuesday.

The state also reported an 8.3% COVID-19 test positivity rate Tuesday, up from 5.8% the day before, an increase that Connecticut Gov. Ned Lamont called “distressing.” Though the governor said he is not so much concerned with the infection rate as he is hospitalizations.

“We have over 500 folks in the hospitals now, so that’s triple where we were a few weeks ago,” Lamont said on the Connecticut Public Radio show “Where We Live” Tuesday morning. “[It’s] one-quarter of where we were a year-and-a-half ago, but it still is reason to be cautious.”

The state’s COVID-19 test positivity rate, which is the highest it’s been in nearly a year, may be elevated due to the use of at-home tests, Juthani said. Negative tests may go unreported, leading to fewer tests overall being factored into the positivity rate. But there is still cause for concern, she said.

“What we can be explicitly clear about is that this is a concerning trajectory that we are headed on in terms of the number of cases we have in our state,” Juthani told WTNH.

The health commissioner attributed several reasons to the recent increase in transmission in Connecticut — and the region in general — including colder weather, waning immunity among vaccinated residents and indoor gatherings, including holiday celebrations.

“You put all of these factors together, and it is not surprising that we see a rise in cases,” she told WTNH. “This virus is equal opportunity, and this virus finds the unvaccinated, primarily, but we do know that breakthrough cases can happen also.”

Over 85% of the state’s population has gotten at least one dose of the COVID-19 vaccine, according to federal data. The “overwhelming majority” of those who are getting infected are unvaccinated, Lamont said. More severe cases are also largely in those who are unvaccinated; of those currently hospitalized, over 76% are not fully vaccinated, according to state data.

“We need to focus on those that are not vaccinated,” Patrick Charmel, president and CEO of Griffin Hospital in New Haven County, told reporters Monday during a press event encouraging vaccination and boosters. “We need folks to go out and protect themselves, because they are protecting the community, but they’re also preserving our capacity to take care of sick people.”

Amid concerns about the new omicron variant, which has been detected in at least two Connecticut residents, Charmel said the predominant delta variant has been contributing to the current surge in hospitalizations in the state.

“What we are seeing right in, in the increase in hospitalizations over the last two weeks … that’s not because of omicron. That’s because of the delta variant that’s still with us,” he said.

Charmel said Monday that 91% of hospital beds in New Haven County were full, leaving 200 available. Influenza cases are also starting to add another “layer” of strain on hospitalizations in the region, and he urged people to get the flu vaccine as well.

“There isn’t the capacity to handle what could come if we don’t do the responsible thing,” Charmel said.

As cases have gone up in recent weeks, Lamont said he isn’t considering implementing any new COVID-19 health orders, such as a universal indoor mask mandate. Currently, only unvaccinated people in the state are required to wear masks while indoors in public spaces. The governor has urged people to avoid large crowds, be cautious and get vaccinated or boosted. He told reporters Tuesday that he is “hopeful” that residents will “continue to do the right thing.”

Juthani has also encouraged people to get their boosters to help reduce transmission. About a quarter of eligible residents have gotten their boosters so far, federal data shows.

“Do not let your guard down,” she said. “This virus is not done with us, even if we’re done with it.”