Researchers have proved the effectiveness of masks with human models, and conducted similar experiments at different distances. It is found that the combination of mask and social distance can significantly reduce the risk of COVID-19 infection when a person comes into contact with an infected person.
Many scientists have conducted simple experiments and studies to prove how masks block tiny particles like SARS-CoV-2, and prove that masks will not pose any safety threat to the wearer. The latest such research concluded that masks play a "key" role in preventing the spread of COVID-19.
Researchers have conducted a series of experiments involving human models to simulate particle transmission with and without masks. As you can see in the following clip, the researchers want to measure the effectiveness of masks in blocking aerosols and droplets. They use mannequins to simulate how infected people spread droplets when wearing any kind of masks (from medical masks to cloth masks). They also studied how mannequins spread the same particle flow without wearing a protective mask.
The researchers also studied the requirements of social distance, and found that the farther the distance between people, the lower the risk of infection, especially in combination with the use of masks.
"We found that the most important measure to reduce the exposure risk of COVID-19 is to wear a mask," said Dr Matthew Callstrom. "We found that disposable paper medical masks and double-layer cloth masks can effectively reduce the spread of droplets, and we did not find any difference in blocking aerosol particles emitted by wearers among mask types."
"The most common transmission mechanism of COVID-19 is through respiratory droplets, which are larger than aerosols and are easier to block with masks." The doctor added.
Both CDC and WHO believe that the virus is mainly transmitted by droplets, and both institutions acknowledge the risks of aerosol transmission. The researchers released the following picture, which compares the size of SARS-CoV-2 virus with that of 2 micron particles, in order to represent the size of aerosol particles that may contain SARS-CoV-2.
The study also measured the different distances of aerosol particles from the source to the target. The researchers found that the number of particles decreased with the increase of distance, and supported the guidance of CDC on keeping social distance, suggesting that the distance between people should be 6 feet. The following figure shows the exposure risks based on masks and social distance. The researchers found that even if the distance between two subjects was more than six feet, the mask would help.
"I think we have a certain understanding of the importance of masks. Some studies have shown that masks can effectively block viruses, but what really matters here is how effective masks are when both sides make masks," said Dr Elle Berbari.
"We objectively found that masks are very important to protect ourselves and people around us," Callstrom said. "If you wear a mask, you are protecting others. If they wear masks, they are protecting you. "
研究人员用人体模型证明了口罩的有效性,并在不同距离进行了类似的实验。研究发现,口罩与社交距离相结合,可以显著降低一个人在接触感染者时感染COVID-19的风险。
此前不少科学家已进行简单的实验和研究,证明口罩是如何阻挡像新冠病毒这样的微小颗粒,并证明口罩不会对佩戴者构成任何安全威胁。最新的此类研究结论是,口罩在预防COVID-19传播方面发挥着 “关键”作用。
研究人员进行了一系列涉及人体模型的实验,以模拟使用和不使用口罩的颗粒传播。正如你在下面的片段中所看到的那样,研究人员想要测量口罩在阻挡气溶胶和飞沫方面的效果。他们使用人体模型来模拟感染者在戴上任何种类的口罩(从医用口罩到布口罩)时如何传播飞沫。他们还研究了人体模型在不戴防护面具的情况下如何传播同样的粒子流。
研究人员还研究了社会距离的要求,发现人与人之间的距离越远,感染的风险就越低,尤其是与口罩的使用相结合。
“我们发现降低COVID-19暴露风险的最重要措施是戴口罩,”Matthew Callstrom博士说。"我们发现,一次性纸质医用口罩和双层布质口罩都能有效地减少飞沫传播,我们没有发现口罩类型之间在阻挡佩戴者发出的气溶胶颗粒方面存在差异。"
“COVID-19最常见的传播机制是通过呼吸道飞沫传播,这种飞沫比气溶胶大,用口罩更容易阻挡。”这位医生补充道。
美国疾控中心和世卫组织都认为病毒主要通过飞沫传播,两个机构都承认气溶胶传播有风险。研究人员发布了以下图片,将SARS-CoV-2病毒的大小与2微米的颗粒进行了对比,意在代表可能含有新冠病毒的气溶胶颗粒的大小。
该研究还测量了气溶胶粒子从源头到目标的不同距离。研究人员发现,粒子数量随着距离的增加而减少,支持美国疾控中心关于保持社交距离的指导意见,建议人与人之间的距离为6英尺。下图显示了基于口罩和社交距离的暴露风险。研究人员发现,即使两个受试者距离超过六英尺,口罩也会有所帮助。
“我想我们对口罩的重要性有一定的了解,已经有一些研究表明口罩能有效阻挡病毒,但这里真正重要的是,当双方都做口罩时,口罩的效果如何,”Elle Berbari博士说。
“我们客观地发现,口罩对于保护自己和周围的人来说是至关重要的,”Callstrom说。“如果你戴着口罩,你是在保护别人。如果他们戴着口罩,他们是在保护你。”
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