Maine’s case counts, hospitalizations and deaths from COVID-19 continue to plummet at the same time the rollout of the state’s vaccination program is accelerating.

The two trends may be related. Or not.

Dr. Nirav Shah, director of the Maine Center for Disease Control and Prevention, said Wednesday that it’s plausible vaccination is already reducing COVID-19 infections, based on the number of Mainers who have received at least one shot, combined with the estimated number who have had the disease and acquired some level of immunity.

“That is one hypothesis for why case numbers may be declining,” Shah said in an interview. “We’re getting to the point where it is becoming biologically possible.”

But other public health experts are skeptical of the vaccine’s role in reducing transmission – at least at this point in the pandemic, with about 15 percent or less of the population in most states having received one dose. In Maine, just over 14 percent of the population has received at least one dose.

More than 180,465 people had received a first dose of vaccine in Maine by Wednesday, and the Maine CDC has recorded nearly 43,000 cases of COVID-19. But the number of people infected with the disease who were not tested, and therefore not included in official case counts, is likely much higher.

Based on some scientists’ estimates, the number for Maine could be in the 100,000 to 300,000 range or even higher. That’s because many people with mild or no symptoms are not tested for COVID-19 and don’t realize they have contracted the virus. Asymptomatic cases are common, especially in young people,  representing about 30 to 40 percent of all cases.

Some research suggests the number of people who have had COVID-19 is five times higher than official statistics, while other studies point to perhaps 10 times more cases than reported.

If 400,000 to 500,000 or more Maine people have been vaccinated or have natural immunity because they’ve been infected, that is approaching the 30 to 50 percent range of the state’s 1.3 million population that experts believe may be the point where immunity starts to slow virus transmission, Shah said.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told reporters Wednesday that early research is indicating the COVID-19 vaccines currently in use – developed by Pfizer and Moderna – are not only preventing people from getting the disease, but also are keeping people from transmitting the virus.

When the vaccines were approved late last year, clinical trials proved that they prevented disease, but it was unknown if the vaccines also stopped people from infecting others.

Shah said there may be multiple explanations for why cases are starting to decline in Maine.

“Could it be seasonality (of the virus)?” Shah said. “Could it be people adhering to masking? Could it be that there haven’t been holiday gatherings recently? Yes.”

When identifying causes for trends in pubic health, he said, the explanation often involves a number of contributing factors as opposed to one dominant reason.

The seven-day average of daily new cases continues to nosedive in Maine and stood at 145 on Wednesday. That’s four times lower than the peak seven-day average of 625 daily new cases reported on Jan. 15. Hospitalizations and deaths also are declining.

Nationally, cases also are plummeting, with the seven-day average of new cases at about 81,000 on Feb. 16, compared to a peak of about 250,000 in mid-January, according to the U.S. CDC.

Joshua Michaud, associate director of global health policy for the Kaiser Family Foundation, a national health policy research center, said in an interview that it’s unlikely that current case trends in Maine and nationally are caused by increased vaccination, although immunizations will drive down cases eventually.

“We can be fairly definitive that vaccines are not the reason why we are seeing declines in cases,” Michaud said. He said one reason is that most of the virus transmission is occurring in people 20 to 50, which is generally not the age group that is being vaccinated. Maine, for instance, is prioritizing those 70 and older, although younger health care workers and public safety workers have also been part of the first wave of vaccination.

Those 70 and older make up about 45 percent of those who have received at least the first dose of the vaccine in Maine, and that group is less likely to come in contact with others, Michaud said, when compared to young people.

He pointed to other potential reasons, such as virus seasonality, people gathering less after New Year’s, and the surge in cases in late December and January scaring people into more closely following physical distancing and masking protocols.

“When we see a spike in cases, people tend to be more careful,” Michaud said.

Additionally, he said people who are more likely to engage in riskier behaviors already may have been exposed to the virus, lowering transmission because that subset of the population has natural immunity.

Dr. James Jarvis, COVID-19 incident commander for Northern Light Health, said he doesn’t believe that Maine has yet vaccinated enough people to have had an impact on case counts, but that eventually vaccines will play a large role in reducing COVID-19 cases.

To reach herd immunity, which would bring cases to near zero and prevent nearly all circulation of the virus, scientists estimate roughly 70 to 85 percent of the entire population would have to be immunized. Shah believes that with the new, more contagious variants circulating, herd immunity will require an 80 percent vaccination rate.

But Maine’s willingness to get the vaccine is among the highest in the nation, with 62 percent saying in a recent U.S. Census survey that they would “definitely” receive a COVID-19 vaccine when one becomes available to them. That’s the ninth-highest in the nation. The national average is 54.8 percent.

Vaccine supply will likely improve in the coming weeks, as the Biden administration accelerates vaccine shipments to states, with a 23 percent increase expected next week, according to a tweet by White House COVID-19 adviser Andy Slavitt.  The Kaiser Family Foundation projects a massive increase in vaccine supplies over the next six weeks, with daily doses administered nationally increasing from 1.7 million currently to 3.3 million by the end of March.

Dr. Sheldon Stevenson, system chief for emergency medicine at Central Maine Healthcare in Lewiston, suspects that vaccinations already may be playing a role in reduced cases.

“I don’t have any proof. I don’t have any data to back this up,” Stevenson said. “There is definitely a correlation, but there’s no proof of causation. But what has changed recently? The difference is we have vaccination in our back pocket.”

Stevenson said he is “very optimistic” about the trajectory of the pandemic heading into the spring and summer, but public health measures such as masking and physical distancing need to continue to crush the virus.

He said another sign that vaccines are having an impact is the lack of recent outbreaks at long-term care facilities. According to the COVID-19 Tracking Project website, Maine has seen only 120 COVID-19 cases at long-term care facilities since Jan. 28. From Dec. 3 to Jan. 21 – a period that roughly coincides with the peak of the pandemic in Maine – there were 2,266 cases of COVID-19 at long-term care facilities in Maine, more than half of the 4,166 total cases since the pandemic began.

“The vaccination program is going to be paying dividends,” Stevenson said. “This is our path out of this.”