CALGARY -- As details about the coronavirus and its spread changes by the minute, it seems advice from health authorities, including here in Alberta, shifts just as quickly.

Hours after Alberta Health Services said Albertans are not advised to wear medical masks when healthy, chief medical officer of health Dr. Deena Hinshaw amended that statement during Friday's daily update.

"We know that masks can limit the spread of infection from someone who is infected to others. We also know, so far, that a small proportion of people with COVID spread the virus before they have symptoms," Hinshaw said.

In general terms, she said masks would more likely do more to protect others from an infected person wearing a mask, but there is an argument to wear them.

"In that vein, I certainly think masks can be considered."

Earlier in the day, the Center for Disease Control (CDC) said it was recommending the usage of medical masks by the general population as a countermeasure against contracting COVID-19.

President Donald Trump followed that advice by announcing new federal guidelines for Americans to support broader usage of the medical masks, despite admitting he would not wear one himself.

“It's a recommendation, they recommend it,” Trump said. “I just don't want to wear one myself.”

Friday's announcement capped an evolution in guidance from the White House that officials acknowledged has at times been inconsistent.

“I want to unpack the evolution of our guidance on masks because it has been confusing to the American people,” said Surgeon General Jerome Adams.

Adams, who had repeatedly and publicly advised against the need for face coverings, said Friday that although he and other public health experts initially believed wearing a mask would not have a substantial impact on curbing the spread, the latest evidence makes clear that people who don't show any symptoms can nonetheless pass on the virus.

What's changed?

Dr. Joe Vipond, an emergency room physician in Calgary, says the main thing that's changed the thinking regarding masks is research that's discovered there are people who are going out in public who feel well and don't have symptoms but are, in fact, contagious.

"There's no way of catching these other than preventing these people from spreading it to others," he says.

Wearing a mask can also prevent individuals from touching their own face despite their best efforts to keep them from doing it, Vipond says.

"It also reminds people of social distancing. When you see people walking around with a mask, you have that visual cue to, 'I better stay away from that person," he says. "Otherwise, we have that sense of complacency where everyone is walking around thinking everything's okay, everything's normal."

Masks are also considered to be another layer of protection against getting sick, he says and aren't required at all if you strictly follow the rest of the recommendations set out by the province.

"If you don't leave the house, there is no way you can get this virus because you're just not getting in contact. But if you have to leave the house – you're a police officer, a health care worker or you have to get your groceries or you're a grocery store worker and you have to go out there – put on those layers. The first layer is physical distancing, keep two metres away from people, the second layer is washing your hands as much as possible – 10 times a day at minimum. Then, throw a mask on there. Don't neglect those other layers – it's all a package."

Cloth or surgical?

When it comes to the effectiveness of the different types of masks, Hinshaw admitted she hadn't looked at the CDC's research into two of them – cloth and surgical.

"The challenge with cloth masks is understanding if they do as good a job as surgical masks in preventing the spread of infection. We know, from some studies that when cloth masks get damp – when someone wears them for a long period of time – they actually begin to trap virus and could be a risk for the person wearing them."

She says her team has now been tasked with examining all the available evidence to determine what are the best masks to prevent being infected by COVID-19 before making a firm recommendation.

"What I wouldn't want to have happen is for people to start to wear cloth masks and inadvertently expose themselves to more risk when what we want to do is lower the risk more broadly."

No matter what recommendations come out, health care workers, who are in the highest risk settings, need to have the surgical and medical masks before anyone else, Hinshaw says.

"That supply issue is one thing to consider. Second of all, if people are considering wearing cloth masks, they need to make sure they are washing their hands very well before they put the mask on and, if they are taking the mask off, they need to wash their hands before they take the mask off and after they put the mask in a place where it can be washed."

Vipond says Albertans should strongly consider the cloth option because the supplies of medical-grade masks must be reserved for health care workers.

"The health care workers are using two kinds of masks; the surgical mask, which is a thin paper mask and then, for the more complicated, what we call aerosolized generating procedures, we have the N-95 mask."

He says the N-95 masks are much more effective at preventing infection and are much more highly valued by health care workers.

Hinshaw said further details and recommendations regarding masks may come sometime next week.

(With files from CTVNews.ca)