MONTREAL -- Quebec's public health director made an unexpected COVID-19 announcement Tuesday: the province is recommending only a single dose of vaccine to people who have previously been infected with the virus.

The move, announced by Dr. Horacio Arruda in response to a reporter's question, appears to make Quebec only the second jurisdiction in the world, after France, to go with this policy.

This winter, several studies suggested that only one dose is needed in previously infected people in order to achieve the same result as two doses in uninfected people.

However, most countries, states and provinces haven't acted on the idea.

Quebec's system still isn't completely clear, either, according to what Arruda said Tuesday, particularly around how long the single-dose window would last for those who have been sick, and how those previous infections would be confirmed.

"What we know is [that] immunity associated to the illness doesn't last a long, long time, and that's why we recommend a second dose," including for those previously infected, said Arruda.

"But if you've already got the illness, and we have lab confirmation of that, we believe that after three months you can get the first dose, which will have the same effect as a second dose," he said.

"We do not recommend a second dose -- the illness, a dose and [another] dose -- because it doesn't bring extra protection, and it brings about more adverse reactions."

He also called the second dose in those cases "not necessary."

While he mentioned waiting three months for the first dose, it was less clear whether this single-dose option would expire after waiting a longer period of time. Some studies have suggested that COVID-19 antibodies drop sharply or disappear several months after the illness.

The Quebec health ministry hasn't yet responded to a request for clarification on the details.

The question isn't yet urgent, practically speaking, in Quebec, since even those who have gotten their first dose are months away from getting the second one, since the province has settled on a four-month delay between the two doses.

Scientists agree that it's crucial for those who have been infected to get at least one dose since their immune system must get a chance to permanently entrench its protection against the virus.

But some studies this winter suggested that just one dose acts as the "booster" shot in those whose immune systems already had naturally developed antibodies against the virus, making a second shot redundant.

“It’s not surprising that the natural infection worked as a primer and the first vaccine dose is a booster,” said the co-author of one of the studies, Dr. Viviana Simon at New York's Mount Sinai Hospital. 

In total, there were three studies that all had similar findings, the New York Times reported in February.

One doctor, writing for the National Institutes of Health in the U.S., wrote later in the month that the findings were encouraging, even though "much more research is needed" and he was "definitely not suggesting a change in the current recommendations right now."

By Feb. 12, however, France's top health authority had recommended going with a single shot after infection, at a moment when the country's leaders were under fire for a slow vaccine rollout.

In Quebec, where more than 303,000 people have been infected, the move will also free up that many doses.

Another question remains in Quebec around how the province will be certain who qualifies.

Arruda also left the door open to giving a single shot to people without lab-confirmed COVID-19 cases, saying the province is planning to merge two databases to help understand who was infected.

Right now, for Quebecers going to get a shot, "You can mention it" if you've been previously infected, he said.

"What will be done as well is that we will merge the test banks with our vaccine registry to check in the labs' file that we have your name with a positive test," he said.

"Then that will show in the vaccination file and... you will be considered as being immune after receiving only one dose."

For those without proof, a single dose is still an option, however, Arruda said.

"During the clinical evaluation, there's a discussion with you to see... Is it really the illness, according to the information that you're sharing"? he said.

"Or they may recommend two doses -- it will be... on a case-by-case basis."

--With files from The Associated Press