These are the hamsters from a widely-shared study used as evidence that masks do work. They aren't wearing any masks.

Surgical masks may help keep hamsters' cages coronavirus-free, but it's still unclear how much extra protection they provide to healthy people, when out and about in the real world.

A new and widely-shared study performed on hamsters, not people suggests that putting a surgical mask in between infected and healthy hammies can help keep many of them virus-free longer, and make their illnesses milder, if they do eventually get sick.

But the hamsters in this study didn't even wear their masks at all, so unfortunately they're not such a great model for our human-sized, coronavirus-infected world.

"I think the big takeaway for me is that we are really desperately looking for data, especially that would be applicable to humans, in a real-world settling," Dr. Abraar Karan, a physician at Harvard Medical School who was not involved in this hamster study, told Insider. "I think a lot of us really want hard data to say masks work."

This study doesn't go quite that far.

Instead, human-sized surgical masks were placed in between the cages of sick and healthy hamsters, as air flowed in one direction only, from sick hamsters (on the left) toward healthy ones (on the right).

hamster masks Jasper Chan, Department of Microbiology, HKU

"You could've put tiny masks on the hamsters!" a disappointed Trevor Noah said on The Daily Show last week .

Despite the lack of adorable, hamster-sized face masks used in this University of Hong Kong study, it still demonstrated that surgical masks help prevent coronavirus transmission.

Professor Yuen Kwok-Yung, a leading infectious disease expert who headed up the hamster study, said during a news conference that this is some of the first good evidence that "we should all wear a mask" until a coronavirus treatment or a vaccine is available.

"Remember, prevention is always better than a cure" he said.

But others aren't quite convinced that draping a mask in front of a critter's cage 24/7 provides a good model for what people do, as they take their masks on and off throughout the course of the day whenever they eat, drink, or unlock their phone , touching them with their hands, and readjusting the fit.

"It's hard to extrapolate from this hamster study to what these masks mean for humans," Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, told Insider. "It is a study that shows surgical masks can prevent droplet respiratory infections from spreading. I think that's basically what it shows. But that doesn't necessarily translate to a public policy prescription for the general public."

Mask-wearing is not universally popular, even though it helps stop infections from spreading

Trump Ford plant.JPG Leah Millis/Reuters

As the coronavirus continues spreading around the globe, face masks are becoming an essential part of getting around, with a majority (63%) of respondents to a May 2020 Morning Consult poll conducted in the US saying they'd feel more comfortable amid this pandemic if businesses required their patrons to wear masks.

But not everyone is wearing a mask out in public , or when braving crowded spaces, and some are downright irate at the suggestion that they should.

The issue has been a tricky one for science to weigh in on definitively, because to date there is not very much gold-standard, scientific evidence that masks really are entirely effective at preventing healthy people from catching viral illnesses.

Even the World Health Organization said recently that healthy people needn't, necessarily, wear masks.

"Obviously if you're sick and you have to go out, you should be wearing a mask," Adalja said. "If you're a healthcare provider, you should be wearing a mask when you're taking care of patients. But I still have a little bit of hesitancy to say that there's strong scientific evidence that actually shows that this decreases transmission in the general public. Most studies have not shown that."

Because it's hard to conduct rigorous studies of people wearing masks, and because it would be pretty unethical to have people wear masks, subject them to a week stuck indoors with others sick with the coronavirus, see whether they get infected, and then cut up their bodies for science, researchers used hamsters for this study.

Hamsters are a surprisingly good model for studies on human diseases

Hamsters, despite their size, are actually great scientific models for human respiratory illnesses. They have been used for more than 60 years to study infectious diseases , because (unlike mice) their respiratory immune response and illness symptoms track pretty closely with those of humans.

However, the conditions that these hamsters lived in, and the way they used their masks, was not so human-style.

"It's a hamster study where the masks are kind of put on the cage," Adalja said. "Which is very different than a person wearing a mask, who is constantly adjusting it. And these were surgical masks, they aren't homemade masks."

It's really easy for hamsters to catch the coronavirus from their roommates, the study found

The study (which is still under review by the peer-reviewed journal Clinical Infectious Diseases ) first put 15 healthy hamsters in cages side by side next to cages filled with five hamsters, already sick with the coronavirus.

Then, the researchers used a fan to blow air in only one direction from the infected hamsters toward the healthy ones.

After a week, 10 of the 15 formerly healthy hamsters were infected, showing just how easy it is to catch the coronavirus through sustained, close contact with others . Sick hamsters who tested positive for COVID-19 the illness caused by the coronavirus became lethargic, backs hunched, and breathing rapidly, the researchers said.

Then, the researchers tried their experiment again, this time on hamsters protected by surgical masks.

The study found masks (used as curtains between cages) reduced the rate of infection by up to 75%

Hamster iStock

In a second and third part of the HKU study, the scientists used human-sized surgical masks as curtain-like barriers between the sick and healthy hamsters.

First, they faced masks away from four sick hamsters, testing whether masks might help prevent coronavirus particles from wafting away from sick hamsters, and getting healthy hamsters sick. Putting 12 healthy hamsters on the other side of the masks, only two of them got sick.

Then, they used surgical masks to protect the healthy hamsters, placing the masks facing away from them, but without putting a mask near the sick hamsters, mimicking what would happen if healthy individuals wore masks, but sick ones didn't. With the healthy side of cages masked, four out of 12 hamsters got sick.

Both experiments showed quite a reduction in the number of hamsters that got sick: a 50% decrease when masks were placed on the healthy hamster side of the partition, and a 75% decrease when masks were put on the sick hamster side. But the study also demonstrates well why public health experts stress it's most important for people who are sick to wear masks , to prevent spreading their viral infections to others.

The masks also resulted in milder illnesses for those that did get sick, and delayed illness onset, suggesting that wearing masks can not only help prevent some infections entirely, but can also make any eventual illnesses more tolerable, and win individuals (in this case, hamsters) more time in close contact, before they get sick.

Whether viral infections are studied in humans or hamsters, masks tend to work best when they're placed on sick people. After all, that's the reason the CDC recommends everyone in the US should wear masks right now, in case they're sick and they don't know it .

The take-home message from this study, according to 2 independent researchers

Though Karan said it's hard to know quite what to take away from this study, because "it's not on humans, and it's not in the real world," he still said it was "interesting" to note how far fewer hamsters were infected over time, when masks were used as a barrier between them and the virus.

"We don't have data to say that masks don't work," he said.

Adalja said he still awaits more solid research on masks, one way or the other.

"There are still some genuine scientific questions that need to be answered regarding the use of masks," he said. "I would say that their impact is marginal compared to hand-washing, refraining from touching your face, and social distancing."