Since the outbreak of COVID-19, this seemingly simple question has caused disagreements between experts and the country: Should members of the public who are not sick use masks to limit the spread of the disease?
For months, the CDC has insisted that the only people who need to wear a mask are those who are sick or are being treated with a mask. This idea stems from the idea that basic medical masks do little to protect the wearer, but mainly to prevent patients from spraying infectious droplets from their noses and mouths. In addition, there is a need to prioritize the allocation of limited supplies to frontline medical staff. The World Health Organization agreed.
But some countries have adopted different strategies, suggesting that masks should be used even when people are away from home in some cases. Many scientists have also begun to suggest that a broader mask policy might be a good idea.
Then, after days of speculation, President Donald Trump announced on April 3 that the CDC recommended that people use cloth face masks in crowded places, even if he emphasized that the measure is voluntary and said he would not follow .
He said: “So, wearing a mask will actually be voluntary.” “You can do it. You don’t have to do this. I choose not to.”
The agency cited new data that “a large proportion” of people infected with the new coronavirus can spread the virus to others even if they have no symptoms. The agency revised the recommendation and said, “Whenever someone has to go, Everyone should wear a cloth face mask. Enter public places.”
The updated CDC website states: “Covering the face with cloth is not to protect the wearer, but to prevent the virus from spreading from the wearer to others.” “This is especially important if someone is infected but has no symptoms.”
Although in the United States, the trend has turned to more cover-ups, some experts have reservations about this policy. There is very little research on cloth masks, and there is not much evidence in the real world to recommend medical masks to the public. If people don’t wear the covering properly, or if they mistake it for a false sense of security, these guidelines may also exacerbate the shortage of medical masks or backfire.
At the same time, other scientists pointed out that laboratory studies have shown that widespread use of masks, and even less effective “do it yourself” models, may still be helpful. And the widespread use of masks may prevent people from touching their faces and help convey the severity of the epidemic.
We will review some of the research and thinking behind the masks and explain why opinions differ. But first, it is important to realize that despite the debate, on the most important issues, most experts agree:
Depending on the design, masks can limit the spread of diseases of infected persons in the so-called source control, and/or can protect the wearers from infection.
As far as COVID-19 is concerned, the spread of the virus is mainly through respiratory droplets. When an infected person coughs or sneezes, the respiratory droplets will fall on the mouth or nose of others. The droplets can also contaminate the surface that other people touch before touching their face.
Here, basic surgical masks-loose disposable masks-may be helpful, because if a sick person wears a mask, its infectious droplets may be trapped in the mask. Doctors and nurses wearing such masks may also be protected because they may be coughed or sneeze.
But the researchers also suspect that the new coronavirus SARS-CoV-2 can stay in the air as very small droplets called aerosols and can be inhaled by people nearby. A study published in the New England Journal of Medicine on March 17 said that aerosol transmission was “reasonable.” In an experiment, it was found that the virus “remains alive” in machine-generated aerosols for up to three hours. Although half of them are not contagious after about an hour. It is not clear how much this mechanism plays in the spread of the virus, and this spread is unlikely to spread the virus over long distances, but scientists are increasingly believing that this virus will happen to some extent.
Margaret Sietsema, a professor of occupational health at the University of Illinois at Chicago, said: “I believe all transmission routes may play a role here, which means that the disease can be inhaled, so the best line of defense It’s a respirator.”
The respirator includes the frequently cited N95 respirator, which is a disposable tight-fitting respirator that can form a seal on the face and includes a special filter that can capture at least 95% of the particles in the air passing through it. (To avoid confusion, we will not call any respirator a mask from now on.)
Compared with N95, surgical masks are not designed to provide protection against aerosols. As the CDC blog explains, surgical masks are “designed to provide barrier protection for droplets, but they do not regulate the efficiency of their particulate filtration, and they cannot form an adequate seal for the face of the wearer who wants to breathe protection.”
Sietsema recently reviewed the mask evidence from the University of Minnesota’s Center for Infectious Disease Research and Policy. He recommended that N95 respirators be used for healthcare workers who interact with COVID-19 patients, but believes that there is insufficient evidence to support a broader mask policy to include healthy people.
She said that masks may be able to reduce transmission by capturing larger droplets from infected people, but this only applies to people with symptoms, and she believes that anyone with symptoms should not be in public places.
She said in an email: “I don’t think masks will reduce transmission before symptoms appear, because the air will never choose a path of greater resistance (through masks), it will only bypass masks,”
She is also concerned that the mask recommendations will cause people to relax their distance from society and may complicate the task of retaining surgical masks for front-line medical staff.
However, other scientists disagree. They say that although masks will not be fully effective, they may be better than nothing.
Benjamin Cowling, an epidemiologist at the University of Hong Kong, does not think that surgical masks are useless to the general public.
He said in an email: “Of course, I can believe that they will be better when used by medical staff, especially when combined with other protective equipment and behaviors, but they are essential when they are worn on the body. This is a big improvement. Used by medical staff, but useless when worn by others.
In a just-published study, Colin co-authored a study in Natural Medicine. Researchers found that surgical masks reduce the number of respiratory viruses expelled when people breathe and cough in special machines.
Previously, another study conducted by Colin and others using a similar setup found that surgical masks reduced the amount of influenza RNA that researchers could detect from smaller and larger respiratory droplets. For larger droplets, the effect is much stronger, but studies have shown that masks can reduce aerosols to a certain extent.
These types of studies have shown that, theoretically, masks can limit the spread of respiratory viruses, but there is still a long way to go before masks are an effective public health measure for the general population.
After all, in actual use, if people are unwilling to alienate from society and end up touching their faces more, or if they keep touching the outside of the mask, the mask may be contaminated and the mask may be harmful.
Even those who support the wider use of public masks admit the lack of such direct evidence. In the “Lancet” respiratory medicine review article, which advocates more “reasonable” use of masks to fight COVID-19, the author describes the existing evidence as “scarce.”
Although some studies have evaluated various masks in hospitals or other health care settings, few people have tested whether masks are effective in the community-there are indeed inconsistencies in masks or no significant effects have been observed.
For example, Cowling told us that the best evidence comes from randomized controlled trials and guided us to conduct a systematic review of 10 trials that tested masks. These trials tested how masks limit the spread of influenza in places such as homes or dormitories. ability. Although many trials are trying to get people to actually wear masks, which suggests that higher compliance may have an impact, the review found that “use of masks does not significantly reduce the spread of influenza.” Many trials are also too small to draw conclusions Any positive conclusions.
Elaine Shuo Feng, a statistician and epidemiologist at the University of Oxford and lead author of the Lancet Respiratory Medicine Review, said: “Based on the summary of randomized controlled trials, there may be some but not great impacts. .” An interview.
She still believes that it is prudent for countries to start considering the use of masks. Feng said: “The lack of sufficient evidence does not mean that the intervention itself is ineffective.” “In this case, I think the best way is to rely on all available non-pharmaceutical interventions.”
In 2015, researchers published the first randomized controlled trial of cloth masks, and found that when medical staff in Vietnam wear masks instead of disposable surgical masks, they are 13 times more likely to develop influenza-like illnesses.
The respiratory tract infection rate of the cloth face mask group was also higher than that of the control group. The control group sometimes wears surgical masks in accordance with hospital standards. However, because no one did not wear a mask at all, the researchers were unable to determine whether cloth masks could still provide some protection for the wearer.
The author wrote: “It was found that the infection rate in the arms of cloth masks was much higher, which could be explained by the effects of cloth masks, medical masks or a combination of the two.”
Other studies have studied how certain fabrics or designs prevent the spread of droplets and particles in the laboratory. However, as the author of the Vietnamese trial pointed out in an article, the paper’s correlation with COVID-19 shows that none of these masks have been tested in clinical trials.
A 2013 study tested household mask materials and found that cotton T-shirts may have a certain filtering ability to filter out bacteria and viruses, but the effectiveness of masks is far inferior to surgical masks. The team concluded that self-made masks are better than no masks, but “should be regarded only as a last resort.”
In a more stringent test in 2010, researchers from the National Institute of Occupational Safety and Health in the United States bombarded T-shirts, towels, sweatshirts and scarves with nanoparticles to evaluate the filtering potential of DIY mask fabrics. Although the performance of this material is reduced compared to N95 gas masks, the author points out that they only provide “marginal respiratory protection”, but most fabrics capture at least some particles.
Linsey Marr, an engineering professor at Virginia Tech, who studies the spread of viruses, warns people not to rely on homemade masks to prevent viruses from inhaling in the air, but for those who pursue their own designs, she has some practical skills.
She told us in an email: “Materials should be thick and densely woven, such as kitchen towels or heavyweight T-shirts, and the mask should be close to the nose and mouth without gaps.”
As the National Academy of Sciences explained in a 2006 report, impromptu masks may be used during a pandemic. A tighter fabric structure may filter better, but there are trade-offs. The report said: “The tightness of the structure increases and the breathing resistance increases, which affects the user’s comfort when using the device.” He pointed out, “This may affect the use.”
For those who choose to wear masks, Feng recommends learning the correct method to reduce accidental infection caused by the mask itself. As shown in the WHO video, the key is not to touch the outside of the mask-if you do, wash your hands.
But the most important thing is not to think that masks can protect you or prevent you from social distancing or washing your hands. As Feng said, this is “better stay at home”.
Answer: There is no evidence that the approved vaccine will cause a decline in fertility. Although clinical trials have not studied this issue, tens of thousands of trial participants have yet to report fertility loss, nor have they confirmed adverse reactions in millions of vaccinators.
Post time: Apr-19-2021
