The highly contagious omicron variant is likely already in Maine even as delta continues to drive rising infections and hospitalizations, the state’s top health official said Thursday.

“Though we have not confirmed the omicron variant in Maine, the Maine CDC believes it is here,” Dr. Nirav Shah, director of the Maine Center for Disease Control and Prevention, said during a media briefing. Thirty-six states as of Thursday, including New Hampshire, had detected the omicron variant, according to federal and state statistics.

Meanwhile, the delta variant that arrived in the summer continues to overwhelm Maine hospitals with record numbers of  patients, most of whom are not vaccinated.

Maine reported 1,286 new cases of COVID-19 and 27 additional deaths Thursday. And a record 381 patients were in Maine hospitals, the CDC reported.

Public health experts predict the more contagious omicron variant could soon be the dominant strain of the disease in the United States. Omicron may cause less severe illness than the delta variant that has fueled the fall surge, but officials say it may add to the burden hospitals are facing because it spreads more easily.

Preliminary studies are showing waning vaccine effectiveness against omicron over time. But they also indicate that booster shots provide similar protection against omicron compared to a fully vaccinated – but non-boosted – person against delta and previous variants.

“Boosters were important before. They are more important now,” Shah said. Maine is now administering about 10,000 shots per day – levels not seen since the spring – with about seven out of every 10 shots being booster shots.

Despite the omicron variant potentially causing another wave of cases, the Mills administration is not considering re-imposing restrictions such as limits on gathering sizes, mask mandates or requiring proof of vaccination to attend indoor events, officials said Thursday. Nine states, including California, have re-imposed mask mandates, and some jurisdictions, such as New York City, now require proof of vaccination to attend many indoor activities.

Jeanne Lambrew, Maine’s health and human services commissioner, said there are “no plans at this time” to bring back any of the pandemic restrictions.

“We do know vaccines appear to be effective against omicron,” Lambrew said. “Our first line of defense is vaccination.”

The omicron variant accounts for about 3 percent of all cases in the United States. But based on how the variant has spread in South Africa and other countries, it has “an extraordinary ability” to transmit quickly, said Dr. Anthony Fauci, White House medical advisor, in an appearance on “Good Morning America” on Thursday.

“It has what we call a doubling time of about three days, and if you do the math on that, if you have just a couple of percentage of the isolates being omicron – very soon it’s going to be the dominant variant,” Fauci said.

Even though illnesses from omicron may be less severe than delta, Shah said, its higher transmissibility means more people may get sick, further overwhelming hospitals.

“When it comes to assessing a variant, contagiousness ranks higher than severity,” Shah said.

Meanwhile, unvaccinated patients sick with COVID-19 continue to strain hospital systems in Maine.

Maine Medical Center in Portland, the state’s largest hospital, is experiencing the largest wave of COVID-19 patients it has seen since the pandemic began.

The 615-bed hospital cared for an average of 52.3 confirmed COVID-19 inpatients each day for the week ending Thursday, up from its previous record set last week of 45.9 per day. On Thursday, it was caring for 58 such patients, just one shy of the all-time single-hospital record of 59 set at Bangor’s Eastern Maine Medical Center in late September.

As has been the case throughout the pandemic, the vast majority of those hospitalized as of Thursday are not fully vaccinated.

There are 381 people in Maine hospitals being treated for COVID-19, with 114 in intensive care and 66 on ventilators, the CDC reported Thursday. It was yet another new pandemic high and marked the 11th consecutive day of at least 350 COVID-19 patients, a trend that has forced many hospitals to postpone elective surgeries such as knee and hip replacements.

MaineHealth, the 10-hospital network that includes Maine Med, reported that only 4 of the 42 COVID-19 patients in intensive care across its system were fully vaccinated against the disease. Only 21 of the 82 inpatients being cared for outside the ICUs were fully vaccinated.

Dr. Joel Botler, Maine Med’s chief medical officer, said the spike is largely due to the growing number of acute COVID-19 patients statewide needing specialized care available only at the Portland hospital, including special oxygenation interventions for people no longer getting enough oxygen while on ventilators.

“With COVID, when people get very ill it is a multi-system illness, not simply a respiratory one, and as that complexity increases, at a certain level they need to come to (Maine Med),” Botler said.

Botler noted the hospital had 19 COVID-19 patients on ventilators at one point Thursday, the highest during the pandemic.

Jennifer McCarthy, Maine Med’s chief operating officer, said capacity at the hospital was incredibly tight, and that cancer and orthopedic patients who would normally be in operating rooms were having to wait many weeks because of the COVID-19 surge.

“We are committed to taking care of the sickest people in the state of Maine, so as people get sicker and the COVID needs increase, we meet that demand by dialing back on anything that can wait a period of time,” McCarthy said.

Other hospitals across the state reported very high numbers of COVID-19 inpatients. Inland Hospital, a 36-bed facility in Waterville, had 6.4 per day, up from its previous record of 6.1 set last week. Mercy Hospital in Portland, Mid Coast Hospital in Brunswick, MaineGeneral Medical Center in Augusta, and Central Maine Medical Center in Lewiston all reported near-record levels of patients.

The high number of deaths reported Thursday includes 20 deaths that were identified through a periodic review of death certificates, in this case in November, according to the Maine CDC. Some of the new infections also occurred over the past week or so but were not immediately processed because of a flood of positive tests.

Several hospitals across the state are getting help this week from the Maine Army National Guard, which deployed 38 Guard members to non-clinical roles. Maine Medical Center in Portland also has been approved to receive a “surge response team” of 15 clinicians from the U.S. Department of Health and Human Services and Central Maine Medical Center in Lewiston hopes to gain approval for a team this week as well.

One of the areas the National Guard will assist with is monoclonal antibodies, which are used to treat COVID-19 patients.

Since the pandemic began, Maine has recorded 134,170 cases of COVID-19 and 1,405 deaths. The seven-day average of daily new cases stood at 1,047 on Thursday, compared with 769 a week ago and 532 a month ago.

On the vaccination front, 945,794 people have received their final dose of COVID-19 vaccine, representing 70.36 percent of Maine’s 1.3 million population. Nearly 400,000 Mainers have received their booster shot.

But there’s a wide disparity in vaccination uptake among counties, and areas with low vaccination rates are fueling the surge. Cumberland County, the most-vaccinated in Maine, is reporting 80.7 percent of its residents are fully vaccinated, compared with lower-vaccination counties like Somerset, Piscataquis and Franklin, which are recording vaccination rates of less than 60 percent.