This study was perfectly written to show a pro-mask point of view.
First and foremost, it is not a randomized controlled trial but rather an after-the-fact, what-do-you remember about your illness study. The researchers conclude, however, that the study (done on only 124 households) confirms that wearing masks will stop COVID-19 transmission and that transmission occurs in the first couple of days after symptom onset because all the primary subjects were hospitalized immediately as per China's policies.
"This study confirms that the highest risk of household transmission is prior to symptom onset, but that precautionary NPIs, such as mask use...can prevent COVID-19 transmission during the pandemic."
Wait a minute... Look at this data published in the study:
Time interval from illness onset to medical isolation (days):
Total Families without Families with
secondary transmission secondary transmission
≤2 32 (25.8) 26 (31.3) 6 (14.6) – Ref
>2 92 (74.2) 57 (68.7) 35 (85.4) 0.05 2.66 (1.00 to 7.12)
So, according to their own data 85.4% of the families that caught COVID-19 from a loved one in their homes had that same loved one in their homes for MORE THAN 2 DAYS. How does that mean you are most likely to get it in the first two days or before symptoms appear?
Now, these researchers were not asking people after the fact if they had caught COVID-19 from the primary case. Nor were they testing everyone in the family to see if they had really gotten COVID-19 from the person during the first two weeks when they could have caught it. No. Instead, a family member had to not only catch COVID-19 from the primary case, but then that person had to have symptoms severe enough that they went to the hospital, have a test confirming it, and where they would then be quarantined for who knows how long. Now, lets say you are family and Dad comes home sick from work with COVID-19. He goes to the hospital and is put there for a minimum of 2 weeks (and probably longer since this was in the first months of the pandemic when everyone thought you could get it for two months afterward). Jr. gets COVID-19 from dad, but at 10 years old he has no symptoms and nobody knows because they never test him. Mom also gets COVID-19 from dad, but she only has minor symptoms and she is already under forced quarantine because dad had it. As a mother, do you (a) go to the hospital (where you will be quarantined) and try to find someone else to watch your son who is supposed to be quarantined from everyone because of his exposure or (b) suck it up and take care of your son and household? Grandma gets COVID-19, but she doesn't have it that badly and doesn't want to go to the hospital, so she spends time in her room using old-school traditional medicine. Voila, no secondary transmission in that family.
Now, lets remember, the WHO tested 70,000 people in the beginning of this and confirmed that the transmission rate among household members was about 80%. This study of 124 families says household transmission is only 23%!!! Wow. There were 26 families that did not have secondary transmission and never wore masks. There were 21 families with secondary transmission that never wore masks. So, 47 families never wore masks and 55% of those families did not have secondary transmission as defined by the study's perimeters. Either WHO and their huge study were wrong or this study is wrong. Considering most of the data in this study did not have statistical significance, I think I will go with WHO.
But let's look at the real mask data they are promoting (as well as the 100+ news agencies that picked this up).
No of family members wearing mask at home before primary case’s illness onset date (median (IQR))
Total Families without Families with
secondary transmission secondary transmission
None 31 (25.6) 27 (33.3) 4 (10.0) – Ref
One or more 90 (74.4) 54 (66.7) 36 (90.0) 0.009 0.22 (0.07 to 0.69)
There is a lot wrong with this data. My first impression was that it is almost identical to the data above concerning how long it took to get into the hospital quarantine. Were the same families that were not wearing masks prior to the onset of the disease also waiting to go to the hospital? If that is true that could invalidate all the data--but this similarity is not mentioned or explained anywhere in the text. Second, why are only 121 of the 124 families recorded here? Third, and this is the most interesting: why isn't the data broken down into "none" "some" and "all"? Or better yet, "all" and "none or not everyone wore a mask"? What the authors are trying to say and what they have statistically proven is that only one person in your family has to wear a mask at all times and the entire family will be safe. If Grandma wears a mask, no one will get COVID-19 according to the way this data is set up and analyzed. Ironically, the authors did divide the categories into "none" "some" "all" for mask use after the illness onset. No reason was given for combining the two categories. This is concerning since one person wearing a mask in a household of four would have questionable effect on disease transmission. It could be argued if the person was the primary case or the only caregiver for the primary case prior to hospital admission, there may be some benefit, but the problem with that scenario is that this statistic is covering mask use before the primary case had symptoms. It is highly unlikely the only person wearing a mask would fall into these two categories. Further, it would be impossible to replicate these results if that happened.
In the yellow journalism that has encompassed the peer-review process, this paper has been cited again and again as well as in news stories.
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