The sign outside Moderna in Cambridge is covered up. Company officials offered more than one explanation

The sign outside of Moderna in Cambridge is covered up.Jessica Rinaldi/Globe Staff

Moderna has long advertised its Kendall Square presence in distinctive lower-case red letters above the front entrance to the biotech’s headquarters. But the familiar sign recently went undercover, shrouded in what looks like white shrink wrap.

It’s a curious move by 10-year-old Moderna, which has assiduously sought news coverage as it tries to develop the first potential vaccine for COVID-19. The Cambridge company has issued press releases so frequently that some critics have accused the drug firm of boosting its stock price through hype to benefit insiders.

But when it comes to a seemingly innocuous question ― why is the sign outside the 200 Technology Square building now hidden? ― the high-flying firm appears less eager to draw attention to itself.

Company officials Tuesday offered more than one explanation for the stealth profile.

In a brief phone call, Moderna spokeswoman Colleen Hussey cited security concerns. But she said she couldn’t discuss the matter further and needed to consult Moderna’s chief corporate affairs officer, Ray Jordan.

Jordan, a former Amgen executive Moderna retained as a communications consultant in the spring and named to its staff last month, lives in Southern California. He said he has only been to the company’s headquarters once and hadn’t heard about the hidden sign until this week. He promised to look into it.

A short while later, he called back to say that Moderna’s landlord, Alexandria Real Estate Equities, had recently cleaned the facade of the building and recommended covering the sign during the process.

Moderna — which has received a pledge of $955 million from the federal government to help develop a coronavirus vaccine ― is also preparing for the landlord to renovate and redesign the building, so it decided to keep the sign under wraps until that work is completed, Jordan added. The Globe found no recent building permits in a Cambridge municipal database.

Jordan repeatedly parried questions about the security concerns mentioned by Hussey, although he acknowledged that might have also had something to do with the sign change.

“Of course there are security concerns with Moderna,” he said. “We engage internal and external security experts regularly.”

He then added, “Am I ruling out that the police may have said, ‘Lower visibility isn’t bad, leave [the covering] here for a few weeks before you start construction’? I don’t know.”

Cambridge police spokesman Jeremy Warnick said he was unaware of Moderna receiving any security threats. FBI spokeswoman Kristen Setera said her agency doesn’t comment on security measures taken by private companies.

But there is no doubt that the race to develop a vaccine to help end the pandemic has raised concerns about international espionage and theft.

Last Tuesday, US officials accused China of sponsoring criminal hackers who are targeting biotech firms around the world working on COVID-19 vaccines and treatments. The FBI said the Chinese government was acting like “an organized criminal syndicate.”

Jordan said Moderna has been in contact with the FBI and been made aware of attempts to hack into the firm’s research on its experimental vaccine.

At least 164 vaccine candidates have been developed worldwide, 25 of which are being tested on humans, according to the World Health Organization. On Monday, Moderna’s vaccine candidate became the first to enter late-stage trials in the United States. The vaccine is expected to be tested on 30,000 volunteers at 87 sites in the country, including Brigham & Women’s Hospital in Boston.

While Jordan gave varying explanations for why Moderna had hidden its headquarters sign, he was more direct about what the company has done at its sprawling manufacturing plant in Norwood, after a Globe reporter drove around the suburban complex Tuesday.

Jordan confirmed that the company has removed signs at the entrance, as well as other places around the complex, which is patrolled by security guards. Moderna hopes to manufacture hundreds of millions of doses of its vaccine at the Norwood plant.

“About two months ago, much of the signage there was either adjusted or removed out of an abundance of caution for security and for the safety of our employees once it was clear that the production facility would become a primary manufacturing point for our vaccine candidate,” he said. “That was without any specific security threats precipitating the action.”

Unlike traditional vaccines, which use a weakened or killed virus to stimulate an immune response, Moderna’s vaccine relies on genetic material called messenger RNA, or mRNA. The vaccine inserts portions of the coronavirus’s RNA into cells, which then manufacture a piece of the virus to generate antibodies.

The company, which has no products on the market — something that’s not uncommon in the biotech world — set a drug industry record by producing its vaccine in 42 days after receiving the genetic sequence of the virus from Chinese researchers. No messenger RNA vaccine has ever been approved to prevent any disease, although Moderna is one of several companies seeking to do so with the coronavirus.

Moderna’s stock price has risen 245 percent since it announced in February that it had designed and produced its first batch of the vaccine candidate.

Tim Logan of the Globe staff contributed to this report.