When trucks arrived at 35 sites across Maine on Monday, workers opened them to inspect hundreds of vials of the Moderna vaccine — another key shipment in the state’s efforts to inoculate residents from the coronavirus.

But when they looked at the electronic thermometers outside the boxes, they quickly found a problem: a red “X” on the monitors’ screens, alerting them that the vials had spoiled because of improper temperatures at some point along the journey.

Now, the state announced Tuesday, it may have to throw out 4,400 doses.

“It’s always unfortunate when logistical issues of this nature crop up but it’s also good to remember that the system has these safeguards in place so that if they happen, we know about them immediately,” Nirav Shah, director of the Maine Center for Disease Control and Prevention, said at a news briefing.

The news came the same day that authorities in Michigan announced that an even larger shipment of the Moderna vaccine containing nearly 12,000 doses had been ruined by temperature control issues during shipment, as reported by the Detroit Free Press.

Those discoveries have prompted separate investigations by the Centers for Disease Control and Prevention, Moderna and a distributor to determine exactly how and why the vials were ruined.

“We are tracking a few incidents of temperature readings outside the acceptable threshold,” Kristen Nordlund, a spokesperson with the CDC told The Post in an email. “In every instance, the process worked – the shipment was inspected and replaced, as needed, while any additional safety reviews were conducted.”

Both cases highlight one of the ongoing logistical problems in distributing coronavirus vaccines, which must be stored between minus-25 degrees Celsius and minus-15 degrees Celsius (minus-13 and 5 degrees Fahrenheit), according to CDC guidance.

In late December, a hospital outside Milwaukee was forced to toss hundreds of vaccine doses when a pharmacist “admitted to intentionally removing the vaccine from refrigeration,” the hospital said. In New York, health-care workers have had to discard vaccine doses in the past weeks after struggling to find recipients who met the state’s eligibility criteria.

The vaccine rollout continues to lag across the country as states, overwhelmed by the high demand and short supply, struggle to inoculate millions of residents. As of Tuesday, 68,914 Maine residents had received a first dose of the coronavirus vaccine — 5.1 percent of the state’s population, according to The Post’s vaccine tracker. The state was allocated 134,000 first doses.

As of Tuesday, 420,144 Michigan residents had received the first dose of the vaccine, which accounted for 4.2 percent of the population that had received the first dose, according to The Post’s vaccine tracker. Michigan has been allocated 947,000 first doses.

Maine officials learned of the potentially compromised vaccines on Monday morning, when vaccination sites called to report that tracking thermometers on the boxes indicated “the required minimum temperature had been exceeded,” Shah said.

By the end of the day, Shah said, 35 of the 50 sites that had received the Moderna vaccine that day reported temperature issues. The sites that were unable to use the vaccines were expected to receive replacement doses on Tuesday and Wednesday, according to Shah.

In Michigan, authorities learned in recent days about thousands of ruined doses through McKesson Corp., a health-care distribution company in charge of shipping coronavirus vaccines to the state. The vials, which were shipped on Sunday, “had their temperature reported as going out of range and getting too cold,” the Michigan Department of Health and Human Services said in a statement.

The discovery has sparked an investigation by McKesson, which said the company learned on Monday that certain deliveries of Moderna vaccines shipped on Sunday “arrived at the sites of administration colder than the low end of the manufacturer’s stated temperature range.”

“McKesson is replacing these vaccines,” David Matthews, a spokesman with the company told The Post in an email. We also identified the root cause of the issue – some of the gel packs used to maintain appropriate temperatures during shipping were found to be too cold – and have taken steps to prevent this from occurring in the future."

The vaccines are currently under quarantine, Matthews added, “waiting for a determination on whether they are viable.”

A review of doses set to ship Monday, McKesson told The Post, found that a “small percentage of those shipments were also impacted by the gel pack issue.” The company did not ship those doses and is expected to replace them within the next 24 hours, Matthews said.

A spokesperson with the state health department told the Free Press no one received a shot of the spoiled vaccine doses.

Most of the replacement shipments were sent late Monday, with the rest expected to arrive Tuesday, according to the state’s health department.

“Although it is unfortunate that this vaccine will not be able to be used, we are pleased that the safeguards put into place to ensure the integrity of the vaccine worked,” said Joneigh Khaldun, Michigan’s chief medical executive and chief deputy director for health. “This is the first report of vaccine potentially being compromised during shipment in Michigan and we are working quickly with the distributor to have replacement vaccine shipped out.”

At a news conference Tuesday, Michigan Gov. Gretchen Whitmer (D) said she was frustrated by the news that vaccines had to be discarded.

“I know we are in a race and every vaccine matters,” Whitmer said. “But that’s not something I can control. It’s not the state of Michigan’s fault. … That’s part of the bumpy road that we are all experiencing nationwide.”

Carolyn Johnson contributed to this report.