我在美国和加拿大都生活和工作了很多年。有很多同事和朋友。和他们讨论口罩的问题的时候，听到最多的就是“专家”说没有任何研究表明口罩在防止这次肺炎传染是有用的。我说，废话，这次肺炎才出现，当然没有任何研究了。但是这次肺炎和流感是的传播方式是一样的，口罩可以防流感就可以防肺炎呀。结果人家指着鼻子告诉我，“专家”说的是连对流感都没有用，“没有任何研究！你的明白？”。这就是为什么我们在流感季节都不带口罩。
后来我和他们讲口罩为什么可以防肺炎（我还在这里发了https://bbs.wenxuecity.com/health/905020.html）。有几个听了。但还有很多人不信。我也就算了，反正是在家呆着。后来CDC建议戴口罩说是可以保护别人，但自愿。我觉得总是向好的一方面发展了。
现在要重启了。又和朋友们聊起了口罩。结果有个家伙说不过我，就问我“Just show me any study support your mask theory”。我回他“Why don't you just use your own brain to think?”后来我一想，我不是也一样相信“专家”们说的，直接就认为没有任何研究表明口罩可以有防护作用。那到底那些研究是怎么说的呢？我就开始自己在网上搜寻那些有关口罩的研究和文章。
结果，的确是一些研究的结果并不支持口罩有用。但很多这样的研究中的实验受测对象并没有认真的带口罩。并且一些研究的样本也不够。但是，细思极恐的是，并不是象专家说的“没有研究支持口罩有用”。很多研究的结论是认为口罩可以在防止流感大爆发时起到很好的作用(这些研究都是在2009年H1N1大爆发期间或之后做的，所以很有说服力)。
特别让我记忆深刻的是一篇2010年发表在American Journal of Infection Control的文章（https://public.lanl.gov/sdelvall/Masks_Schools.pdf）。开篇就写道：
- There is sufficient evidence indicating that masks, if worn properly and consistently, are an effective nonpharmaceutical intervention in the control of disease spread. The use of masks during a pandemic can minimize the spread of influenza and its economic impact, yet mask-wearing compliance in adults is often poor. Educating the public on the effectiveness of masks can increase compliance whilst reducing morbidity and mortality...（有足够的证据表明，正确且始终如一地佩戴口罩，是有效的非药物手段干预控制疾病传播。大流行期间使用口罩可以最大程度地减少流感和它的经济影响，但成年人戴口罩的依从性通常很差。向公众宣传口罩的有效性，可以增加依从性，同时降低发病率和死亡率。。。）
“最大程度地减少流感和它的经济影响”，“向公众宣传口罩的有效性”，“降低发病率和死亡率”，看到这个，再想想今天的状况，心里不是滋味。这是在2010年美国发表的。到了2020年，尽然变成了没有证据了，还做反向宣传。我不知道我们的“专家”和政府为什么向我们隐瞒，事实上是有很多研究支持口罩在防疫中的作用的。有的研究还显示作用是非常明显的。而且有的研究还是关于自治口罩的。就算一开始口罩买不到，政府也可以让我们自己做呀，而不是骗我们。美国和加拿大都隔离了这么久，在轻症不检测的情况下每天感染的人数和死亡人数没有明显减少，难道就没有想想为什么吗？现在又要重启了。如果不告诉大家真相，让大家戴口罩，在疫苗出来之前，情况会更糟的。在这么多人失去了生命之后，我希望他们可以给我们一个解释，为什么向我们隐瞒。
不说了。下面是我看到的一些research和文章。还有很多。我只是列出了一些。
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https://link.springer.com/article/10.1186/1471-2334-12-26
Conclusions
Results suggest that household transmission of influenza can be reduced by the use of NPI, such as facemasks and intensified hand hygiene, when implemented early and used diligently. Concerns about acceptability and tolerability of the interventions should not be a reason against their recommendation.
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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2818714/
.....
We can conclude from our model that, if worn properly, facemasks are an effective intervention strategy in reducing the spread of pandemic (H1N1) 2009.
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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3591312/
......
Surgical masks reduced the overall number of RNA copies by 3.4 fold. These results suggest an important role for aerosols in transmission of influenza virus and that surgical facemasks worn by infected persons are potentially an effective means of limiting the spread of influenza.
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https://public.lanl.gov/sdelvall/Masks_Schools.pdf
This isn't a research but an interesting article published on [American Journal of Infection Control] in 2010. It begins with this:
There is sufficient evidence indicating that masks, if worn properly and consistently, are an effective nonpharmaceutical intervention in the control of disease spread. The use of masks during a pandemic can minimize the spread of influenza and its economic impact, yet mask-wearing compliance in adults is often poor. Educating the public on the effectiveness of masks can increase compliance whilst reducing morbidity and mortality.
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https://www.cambridge.org/core/journals/epidemiology-and-infection/article/hand-hygiene-and-risk-of-influenza-virus-infections-in-the-community-a-systematic-review-and-metaanalysis/6756C5600F18C0487CA379AAB773F3F8/core-reader
.....
The combination of hand hygiene with facemasks was found to have statistically significant efficacy against laboratory-confirmed influenza while hand hygiene alone did not.
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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3810906/
......
Wearing a face mask was a protective factor against influenza infection.
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https://journals.sagepub.com/doi/abs/10.1177/003335491012500206
... mask wearing was associated with reduced secondary transmission and should be encouraged during outbreak situations.
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https://www.cambridge.org/core/journals/disaster-medicine-and-public-health-preparedness/article/testing-the-efficacy-of-homemade-masks-would-they-protect-in-an-influenza-pandemic/0921A05A69A9419C862FA2F35F819D55
.....
Results
The median-fit factor of the homemade masks was one-half that of the surgical masks. Both masks significantly reduced the number of microorganisms expelled by volunteers, although the surgical mask was 3 times more effective in blocking transmission than the homemade mask.
Conclusion
Our findings suggest that a homemade mask should only be considered as a last resort to prevent droplet transmission from infected individuals, but it would be better than no protection.
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