Despite assurances from Vice President Mike Pence that all Grand Princess cruise ship passengers quarantined at Travis Air Force Base would be tested for COVID-19, The Chronicle has learned that two-thirds of them have declined, often at the encouragement of federal health officials.

As of Wednesday, 568 of the 858 passengers screened while confined turned down the test, a federal official familiar with the Travis quarantine and testing told The Chronicle. The low testing numbers align with what passengers were told by officials during a Tuesday afternoon teleconference, citing a 30% acceptance rate for the novel coronavirus test, several passengers told The Chronicle.

“These folks know they are in a 14-day quarantine, if they test positive they are further delayed until they test negative,” said the official, who The Chronicle agreed not to name because they were not authorized to speak to the media, in accordance with the paper’s ethics policy. “They don’t want to stay. They want to be released.”

Those who spoke to The Chronicle said federal health officials dissuaded them from taking the test, saying if they had no symptoms during the mandatory 14-day quarantine, a test was unnecessary. The federal official and cruise passengers also said the test compliance would have been higher had tests been available to administer shortly after they were removed from the ship and sent to the base.

The low test numbers fly in the face of what government officials had promised after the passengers, many California residents, were removed from the stricken Grand Princess cruise line beginning March 9 and sent to military facilities across the country. Twenty-one people aboard the cruise ship tested positive while it was quarantined off the coast of California before docking at the Port of Oakland.

“We will be testing everyone on that ship,” Pence said March 6 in a White House briefing. Two days later, the U.S. Department of Health and Human Services, which is overseeing the Travis operation, also said passengers would be tested.

But it appears that most will return to their homes with no COVID-19 test results.

In response to a series of questions, a White House official told The Chronicle: “No one can be forced to be tested. All passengers were screened and all were offered testing.”

However, past court rulings indicate the government would be allowed to order testing for the coronavirus during a health emergency, said Dorit Reiss, a law professor at UC Hastings in San Francisco.

Stanford law professor Michelle Mello agreed, saying the government could force a test if there was an order that explained “why testing is reasonable and necessary.”

“Strictly speaking, people do not have to comply with such orders, in the sense that we don’t strap people to a hospital gurney and extract biospecimens from them,” Mello said in an email. “But if they refuse, public health authorities can order them into isolation until such time as the period of dangerousness (contagiousness) has passed. They can also criminally prosecute them and seek imprisonment or fines.”

Brian Ferguson, a spokesman for California’s Office of Emergency Services, said the state was told early on that passengers would be isolated and that those with underlying conditions, symptoms or higher risk factors would be tested.

A statement from the Health and Human Services department said that the federal government can’t force anyone to be tested, but said those at Travis can still opt for testing at a later date. The Centers for Disease Control and Prevention did not return requests for comment.

“I don’t know if the governor of California knows they are not required to be tested when they are released into the community,” the federal official said. “In reality, I don’t know if anyone knows that they can decline.”

Infectious disease experts say so little is known about coronavirus that there are no “binary answers” about whether testing should be required before someone is released from quarantine.

“You don’t want to have 800 or so people re-seeding their communities when they are released,” said George Rutherford, a UCSF professor of epidemiology. “There aren’t absolutes ... a person could be mildly symptomatic or asymptomatic and still infectious.”

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Rutherford called the claims that federal test administrators were dissuading passengers from getting tested “crazy.”

John Swartzberg, a UC Berkeley infectious disease expert, said it’s likely a 14-day quarantine would be sufficient, but he has other worries.

“I am concerned that we continue to get false information from Pence and others,” Swartzberg said in an email. “I am not concerned about the passengers as long as they are being released after 14 days of quarantine (past the incubation period).

The CDC reported that the incubation period lasts two to 14 days. However, some studies have indicated the contagious period could last longer.

The situation developed around March 13 after all the passengers had arrived at the Fairfield air base and federal officials wanted to begin swab testing. The tests were delayed, however, due to a lack of trained personnel, protective gear and test kits, the federal official said.

“If they had been prepared and given us the option from day one we were here, there would’ve been a much higher acceptance,” said former Grand Princess passenger Robert Archer, who has been isolated with his wife, Marlene.

With a March 24 release date looming, the couple turned down the test Sunday. The tests were in a collection phase and it would have taken days for the test to come back, Archer said.

“If no results were back by (our release date), we’ll get delayed,” he said. “If we get tested positive, then we’re not released until we get two or three negative tests in a row, each with its own delay.”

Passengers were told when they arrived at Travis that it would be a 14-day quarantine. If you had no symptoms during that period, Archer said, “you were guaranteed your freedom.”

“We’ve all been clinging to that,” he said. “For people here, the breaking point is fast approaching. The food is degrading. People are on edge.”

Swartzberg called the delay in test availability for not just Travis, but the entire country, “reprehensible.”

“The blame goes squarely on the executive branch of our government and two of its agencies, the (Food and Drug Administration) and the CDC,” the professor said.

The federal official said at other bases with smaller Grand Princess contingents, the test decline rate was much lower.

Since arriving at Travis, about 20 passengers have shown symptoms and have been quarantined away from others. Some of those people have tested positive. Many of those individuals, the federal official said, had access to common spaces at Travis with those refusing tests.

On Tuesday, six passengers in the larger population group were taken away by ambulance, the federal official said.

On Sunday morning, testers knocked on passenger Michelle Heckert’s door. Later that day, despite being told it was unnecessary, Heckert and her grandparents got swabbed.

“The CDC rep said don’t take the test if you are asymptomatic,” Heckert recalled. “They said 14 days is a generous amount of time for symptoms to manifest if you had it.”

She said she was told it would take four to five days for results. Her family’s release date is March 23.

“We just wanted to feel safe … for peace of mind,” Heckert said. “And we wanted to be able to tell people we’d been tested when we were able to be released.”

Many passengers were surprised that declining the test was even an option, she said.

As of Wednesday, the testing of those who wanted it was completed, but no test had yet been returned due to a backlog. There are only 13 staffers at Travis trained to administer the test, and the base was still waiting for required protective gear to be delivered, the federal official said.

Archer’s anxiety has been rising with each day. He said there’s been an average of three ambulance evacuations each day.

If they get out, Archer said he and his wife would return to their Excelsior District home and shelter in place like everyone else in the Bay Area, but they’d have their own beds, food and surroundings. And they wouldn’t be sharing facilities with other higher-risk Grand Princess passengers.

“It’s the same problem: There’s one guideline by the federal government, another guideline from the state and another guideline from the local government,” Archer said. “It’s amounted to one big pissing match.”

Staff writer Bob Egelko contributed to this report. Matthias Gafni is a San Francisco Chronicle staff writer. Email: matthias.gafni@sfchronicle.com Twitter: @mgafni