whiterock said:
Sam Lowry said:
whiterock said:
The SA study says masks do not stop community spread.
Masks did not stop community spread anywhere. Because they can't. Because Science.
If masks did stop community spread anywhere in the world, we await enlightenment.
The SA study doesn't purport to address that question one way or another.
That the authors did not purport, does not mean the study doesn't address the question, because it clearly does. Just as most others do:
"Results: Case growth was not significantly different between mandate and non-mandate states at low or high transmission rates, and surges were equivocal......
Conclusions: Mask mandates and use are not associated with slower state-level COVID-19 spread during COVID-19 growth surge....."
https://www.medrxiv.org/content/10.1101/2021.05.18.21257385v1.full.pdf
"Results: When adjusting for traffic activity, total statewide caseload, public health complaints, and mean temperature, the daily caseload, hospital bed occupancy, ICU bed occupancy, ventilator occupancy, and daily mortality remained higher in the postmask period.
Conclusions: There was no reduction in per-population daily mortality, hospital bed, ICU bed, or ventilator occupancy of COVID-19-positive patients attributable to the implementation of a mask-wearing mandate.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8395971/
Even where studies recommend masks, they are typically clear to indicate that masks can only be effective against droplets, as we see here: https://pubmed.ncbi.nlm.nih.gov/33431650/ Problem is, droplets are are not the primary means of transmission. Certainly, one could argue that the reason transmission is primarily via aerosolized virus is because of mask use which eliminates droplets. But then one would have to then look at the studies of mandates. And when one does that, one sees no difference in outcomes in areas with or without mask mandates.
Clear implication: Reducing droplet transmission is ineffective at preventing spread of CV.
CV spreads so effectively via aerosolized virus that stopping droplets makes no difference.
The authors of the SA study disagree with you. Since you don't believe me, I'll quote from your link again:
Quote:
First, we are only assessing the effect of the mask order itself. In other words, we are not able to assess the actual mask use because we do not have data on adherence to the mask order. Although we adjusted our model for public health complaint calls, we do not have a direct measure of wear....It also is possible that the order did not meaningfully alter mask utilization patterns because mask use was not novel in San Antonio or Bexar County.
As for your other sources, the first is a non-peer-reviewed article with numerous misrepresentations and methodological flaws. It was published in an online journal of little significance and quickly made the rounds among the uninformed. A review of its extensive problems can be found
here.Your last source is my favorite because it's the same one I've already linked on this thread twice. Since you obviously haven't read it, it's worth reviewing in some detail.
First, it expressly does not indicate that masks can only be effective against droplets. In discussing respiratory particles, it defines them as follows:
Quote:
We will thus refer to these respiratory emissions as "respiratory particles" with the understanding that these include particles that are transmitted through the air in a manner beyond the "ballistic trajectories" traditionally assumed of respiratory droplets and thus include aerosols that can remain suspended in the air.
The paper gives an overview of studies on mask effectiveness, including the following:
Quote:
-Wu reported on experiments that showed a cotton mask was effective at stopping airborne transmission, as well as on observational evidence of efficacy for health care workers.
-Face masks were 79% effective in preventing transmission, if they were used by all household members prior to symptoms occurring.
-In a systematic review sponsored by the World Health Organization, Chu et al. looked at physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2. They found that "face mask use could result in a large reduction in risk of infection."
-A Cochrane review on physical interventions to interrupt or reduce the spread of respiratory viruses included 67 RCTs and observational studies. It found that "overall masks were the best performing intervention across populations, settings and threats."
-MacIntyre and Chughtai published a review evaluating masks as protective intervention for the community, protection for health workers, and as source control. The authors conclude that "community mask use by well people could be beneficial, particularly for COVID-19, where transmission may be pre-symptomatic. The studies of masks as source control also suggest a benefit, and may be important during the COVID-19 pandemic in universal community face mask use as well as in health care settings."
-The Usher Institute incorporated laboratory as well as epidemiological evidence in their review, finding that "homemade masks worn by sick people can reduce virus transmission by mitigating aerosol dispersal. Homemade masks worn by sick people can also reduce transmission through droplets."
-Leffler et al. used a multiple regression approach, including a range of policy interventions and country and population characteristics, to infer the relationship between mask use and SARS-CoV-2 transmission. They found that transmission was 7.5 times higher in countries that did not have a mask mandate or universal mask use, a result similar to that found in an analogous study of fewer countries.
-Another study looked at the difference between US states with mask mandates and those without, and found that the daily growth rate was 2.0 percentage points lower in states with mask mandates, estimating that the mandates had prevented 230,000 to 450,000 COVID-19 cases by May 22, 2020.
-The approach of Leffler et al. was replicated by Goldman Sachs for both US and international regions, finding that face masks have a large reduction effect on infections and fatalities, and estimating a potential impact on US GDP of 1 trillion dollars if a nationwide mask mandate were implemented.
-A paper in the American Journal of Respiratory and Critical Care Medicine which analyzed Google Trends, E-commerce, and case data found that early public interest in face masks may be an independently important factor in controlling the COVID-19 epidemic on a population scale. Abaluck et al. extend the between-country analyses from a cost perspective, estimating the marginal benefit per cloth mask worn to be in the range from US$3,000 to US$6,000.
-A study of COVID-19 incidence in Hong Kong noted that face mask compliance was very high, at 95.7 to 97.2% across regions studied, and that COVID-19 clusters in recreational "mask-off" settings were significantly more common than in workplace "mask-on" settings.
-Stutt et al. explain that it is impossible to get accurate experimental evidence for potential control interventions, but that this problem can be approached by using mathematical modeling tools to provide a framework to aid rational decision-making. They used two complementary modeling approaches to test the effectiveness of mask wearing. Their models show that mask use by the public could significantly reduce the rate of COVID-19 spread, prevent further disease waves, and allow less stringent lockdown measures.
-Prather et al. stated that aerosol transmission of viruses must be acknowledged as a key factor leading to the spread of infectious respiratory diseases, and that SARS-CoV-2 is silently spreading in aerosols exhaled by highly contagious infected individuals with no symptoms. They noted that masks provide a critical barrier.
-Vanden Driessche et al. used an improved sampling method based on a controlled human aerosol model. By sampling a homogeneous mix of all of the air around the patient, the authors could also detect any aerosol that might leak around the edges of the mask. Among their six cystic fibrosis patients producing infected aerosol particles while coughing, the airborne Pseudomonas aeruginosa load was reduced by 88% when wearing a surgical mask compared with no mask.
-Wood et al. found, for their 14 cystic fibrosis patients with high viable aerosol production during coughing, a reduction in aerosol P. aeruginosa concentration at 2 m from the source by using an N95 mask (94% reduction, P < 0.001), or surgical mask (94%, P < 0.001).
-Stockwell et al. confirmed, in a similar P. aeruginosa aerosol cough study, that surgical masks are effective as source control.
-Multiple simulation studies show the filtration effects of cloth masks relative to surgical masks. Generally available household materials had between a 58% and 94% filtration rate for 1-micrometer bacteria particles, whereas surgical masks filtered 96% of those particles. A tea cloth mask was found to filter 60% of particles between 0.02 micrometers and 1 micrometer, where surgical masks filtered 75%. Simulation studies generally use a 30 L/min or higher challenge aerosol, which is around about 3 to 6 times the ventilation of a human at rest or doing light work. As a result, simulation studies may underestimate the efficacy of the use of unfitted masks in the community in practice.
-Anfinrud et al. used laser light scattering to sensitively detect the emission of particles of various sizes (including aerosols) while speaking. Their analysis showed that visible particles "expelled" in a forward direction with a homemade mask consisting of a washcloth attached with two rubber bands around the head remained very close to background levels in a laser scattering chamber, while significant levels were expelled when speaking without a mask.
-Research focused on aerosol exposure has found all types of masks are at least somewhat effective at protecting the wearer. Van der Sande et al. found that "all types of masks reduced aerosol exposure, relatively stable over time, unaffected by duration of wear or type of activity," and concluded that "any type of general mask use is likely to decrease viral exposure and infection risk on a population level, despite imperfect fit and imperfect adherence."
I could go on, but hopefully you get the idea. Again this is the article that you cited.
The bottom line is that, yes, there is contradictory evidence, but the weight of good quality evidence supports the benefit of masks against both droplets
and aerosols.
