Hello, Welcome to my channel Medicine with Dr. Moran. If you've not been here before my name
is Dr. Keith Moran. Do masks really help? You have been told they are for Covid-19 but there
actually is very little good quality evidence surrounding masking in the general population.
Today I want to talk about a randomized clinical trial that looks at masking and Covid-19. This
is a very important study because it truly gets at whether masks are effective with this illness
and what type of mask is best. Most people who wear masks use a cloth mask.
People were told that this is helpful but we don't have medical evidence to support this. This
type of trial ideally should have been done much earlier in the pandemic. This is the study I want
to talk about. The study protocol was reviewed and approved at Yale university and by the Bangladesh
Medical Research Council. The funding of the study was a grant from GiveWell.org,
a California nonprofit. They had no role in the study design, interpretation of results,
or decision to publish. This study has not yet been peer reviewed. It is a pre-print currently.
The study is well done and it is overdue. The study was what we call a cluster randomized trial
in rural Bangladesh from November 2020 to April 2021. The predominant variant circulating at the
time was the Alpha or the UK variant. There was very little immunity in this population.
It was done earlier in the pandemic and there were no vaccinations being given.
They looked at 600 villages involved with the total number of people 342,126 adults.
There were three groups. There was a control group that did not receive any interventions,
there was a group that were randomized to surgical masks, and a third group that were randomized to
cloth masks. All of the villages in one area would belong to one of the groups so that there
would not be a lot of intermingling of people from one group to another. These were the masks used.
The cloth mask had three layers. An external exterior layer of 100% non-woven polypropylene
and two interior layers of cotton polyester knit with a nose bridge. The surgical mask had
three layers of 100% non-woven polypropylene with a nose bridge. The filtration efficiency was 37%
for the cloth masks and 95% for the surgical masks. This actually was measured using a
particle counter to see what percentage of particles on the order of 0.3 to 0.5
microns would come through the mask at a velocity of 8.5 centimeters per second. The size of the
virus for comparison is smaller at 0.1 microns. Now N95 masks will filter 99.8% of particles
0.1 microns. In the villages who wore masks masks were distributed at markets or mosques.
Mask wearing was promoted in public spaces there was role modeling and advocacy by local leaders
including in Inams discussing the importance of mask wearing at Friday prayers. Now for the
results. First physical distancing was assessed. In the control villages 24.1% practice physical
distancing compared to 29.2% in the villages that use cloth or surgical mask which was an increase
of 5.1%. The increase in physical distancing was similar in the cloth versus surgical masks at 4.4%
versus 5.4% which was not statistically different. So in this study mask wearing and physical
distancing complements rather than substitutes. This is contrary to concerns that mask wearing
might promote risk compensation and less physical distancing but this was not seen in the study.
In all of the groups numerous observations were taken. In the control group 13.3% of people wore
masks properly. In the treatment villages where they used either cloth or surgical masks 42.3%
of people wore their masks properly. This tripling of mask usage was sustained during
the eight-week intervention and for a couple of weeks afterwards so even in
the groups of villages where there was masking the masking rate was not 100% but only 42.3%.
Physical distancing increased as I mentioned from 24.1% in the control villages up to 29.2% in the
villages that were masked. There were 335,382 participants who completed the symptoms survey.
27,166 which is 8.1% reported experiencing a Covid like illness during the study. This was 13,893 or
8.6% in the control villages versus 13,273 or 7.6% in the intervention villages. 40% of symptomatic
participants agreed to blood collection. They were then tested for IgG antibodies two SARS Cov2.
This slide shows the data. They found that people with symptoms and positive antibodies were noted
in 0.76% of control villages and 0.69% in the intervention villages. These numbers do omit the
number of people who didn't consent for blood tests so the true rate of people with symptoms
and antibodies probably would have been two and a half times higher assuming the non-consenter had
similar likelihood of a positive test. This slide shows the intervention effect. Here
you can see that in the control group listed as comparison villages 0.76% of the total number
of people had symptoms and positive antibodies. Now in the cloth mask villages this was 0.74%
which is a very very small reduction which was not statistically significant.
In contrast in the surgical mask villages there was a reduction of 11.2% down to a level of 0.67%
which did achieve statistical significance. The p-value as we say is 0.043 which means that the
likelihood of this occurring by chance was 4.3% and the probability that this is real
would be the opposite which is 95.7%. They point out that this reduction could have been
more if more people wore masks as only 42% in the masking groups actually wore the masks properly.
This of course is speculation. That might be the case or it might not be.
It's also important to note that after five months the impact of masking did wane
but it did remain higher than the control group about 10% higher. It was in the low 20s
down from the 42% Thus the intervention was not sustained even though it was helpful. I think what
the study definitely shows is that surgical masks are better than cloth masks as one might expect.
This study showed that cloth masks actually weren't very helpful. The study also demonstrated
that doing a study in the middle of a pandemic is possible. This study shows that we desperately
need other randomized trials with masks to tease out who actually benefits from masking.
This likely does not have an all yes answer meaning that everyone should mask. There may be
an age above where masking is helpful. For example do young children in daycare benefit from masking
we don't know the answer to that because we have no trials and of course there are significant
downsides to masking young children. The age where the WHO recommends mask be worn is different from
what the CDC in America recommend in the UK kids below 12 were never mandated to wear
masks. I understand kids of course typically wear cloth masks and this study from Bangladesh showed
that the cloth masks in adults did not work so they probably may not in young kids as well.
Now would surgical masks work in this population? Again we don't know. You also have the question
about whether it's even worth masking children who have such a low infection fatality rate.
The infection fatality rate is the odds of dying if they get infected and for kids
it's on the order of 1 in 120,000. Many young children have already had the virus and have
developed immunity although this obviously varies from place to place. The higher the immunity
the tougher it would be for the vaccine to have an impact. Now what about university students
with vaccination rates of close to 100% in many parts of the world with high vaccination rates
the risk reduction using masks will certainly be smaller because we know vaccinated people
transmit less than unvaccinated people. So the question is how beneficial are surgical
masks and highly immune populations what about scenarios where the community prevalence is low
these obviously require other studies I think the bottom line from this study is that when you need
to wear a mask you should wear a surgical mask not a cloth mask. If someone is a very high risk such
as an immunocompromised person an N95 would be expected to be even better. Thank you for
watching today on Medicine with Dr. Moran. I'm Dr. Keith Moran. Get healthy and stay healthy.