Two reports cover masks, bubbles, rapid tests and other measures that work
Edited by Will Collette
As the world-wide COVID pandemic goes on, scientists around the world are taking hard, critical looks at measures we can all take NOW that can stem the tide now that we have realistic hope for safe and effective vaccines.
By Matt Davies, Newsday
I have put together two research articles because they essentially offer the same thing: practical information on ways to stay safe.
As Dr. Tony Fauci keeps saying, we all need to be patient and follow good public health practices that, with every new study, we know to be science-based and sensible.
Please continue for these two timely reports.
Social bubbles and masks more situation-dependent in terms of effectiveness
Simon
Fraser University
Summary:
Researchers
have found that physical distancing is universally effective at reducing the
spread of COVID-19, while social bubbles and masks are more
situation-dependent. The researchers developed a model to test the
effectiveness of measures such as physical distancing, masks or social bubbles
when used in various settings.
Simon
Fraser University professors Paul Tupper and Caroline Colijn have found that
physical distancing is universally effective at reducing the spread of
COVID-19, while social bubbles and masks are more situation-dependent.
The
researchers developed a model to test the effectiveness of measures such as
physical distancing, masks or social bubbles when used in various settings.
Their
paper was published Nov. 19 in the journal Proceedings of the National
Academy of Sciences of the United States of America (PNAS).
They
introduce the concept of "event R," which is the expected number of
people who become infected with COVID-19 from one individual at an event.
Tupper
and Colijn look at factors such as transmission intensity, duration of
exposure, the proximity of individuals and degree of mixing -- then examine
what methods are most effective at preventing transmission in each
circumstance.
The
researchers incorporated data from reports of outbreaks at a range of events,
such as parties, meals, nightclubs, public transit and restaurants. The
researchers say that an individual's chances of becoming infected with COVID-19
depend heavily on the transmission rate and the duration -- the amount of time
spent in a particular setting.
Events
were categorized as saturating (high transmission probability) or linear (low
transmission probability). Examples of high transmission settings include bars,
nightclubs and overcrowded workplaces while low transmission settings include
public transit with masks, distancing in restaurants and outdoor activities.
The
model suggests that physical distancing was effective at reducing COVID-19
transmission in all settings but the effectiveness of social bubbles depends on
whether chances of transmission are high or low.
In
settings where there is mixing and the probability of transmission is high,
such as crowded indoor workplaces, bars and nightclubs and high schools, having
strict social bubbles can help reduce the spread of COVID-19.
The
researchers found that social bubbles are less effective in low transmission
settings or activities where there is mixing, such as engaging in outdoor
activities, working in spaced offices or travelling on public transportation
wearing masks.
They
note that masks and other physical barriers may be less effective in
saturating, high transmission settings (parties, choirs, restaurant kitchens,
crowded offices, nightclubs and bars) because even if masks halve the
transmission rates that may not have much impact on the transmission
probability (and so on the number of infections).
The
novel coronavirus is relatively new but the science continues to evolve and
increase our knowledge of how to effectively treat and prevent this highly
contagious virus. There is still much that we do not know and many areas
requiring further study.
"It
would be great to start collecting information from exposures and outbreaks:
the number of attendees, the amount of mixing, the levels of crowding, the
noise level and the duration of the event," says Colijn, who holds a
Canada Research Chair in Mathematics for Evolution, Infection and Public
Health.
Frequent,
rapid testing could cripple COVID-19 within weeks, study shows
Research
shows test turnaround-time, frequency far more important than sensitivity in
curbing spread
University of Colorado at Boulder
Testing
half the population weekly with inexpensive, rapid-turnaround COVID-19 tests
would drive the virus toward elimination within weeks -- even if those tests
are significantly less sensitive than gold-standard clinical tests, according
to a new study published today by University of Colorado Boulder and Harvard
University researchers.
Such
a strategy could lead to "personalized stay-at-home orders" without
shutting down restaurants, bars, retail stores and schools, the authors said.
"Our
big picture finding is that, when it comes to public health, it's better to
have a less sensitive test with results today than a more sensitive one with
results tomorrow," said lead author Daniel Larremore, an assistant
professor of computer science at CU Boulder. "Rather than telling everyone
to stay home so you can be sure that one person who is sick doesn't spread it,
we could give only the contagious people stay-at-home orders so everyone else
can go about their lives."
For
the study, published in the journal Science Advances, Larremore
teamed up with collaborators at CU's BioFrontiers Institute and the Harvard
T.H. Chan School of Public Health to explore whether test sensitivity,
frequency, or turnaround time is most important to curb the spread of COVID-19.
The
researchers scoured available literature on how viral load climbs and falls
inside the body during infection, when people tend to experience symptoms, and
when they become contagious.
They
then used mathematical modeling to forecast the impact of screening with
different kinds of tests on three hypothetical scenarios: in 10,000
individuals; in a university-type setting of 20,000 people; and in a city of
8.4 million.
When
it came to curbing spread, they found that frequency and turnaround time are
much more important than test sensitivity.
For
instance, in one scenario in a large city, widespread twice-weekly testing with
a rapid but less sensitive test reduced the degree of infectiousness, or R0
("R naught"), of the virus by 80%. But twice-weekly testing with a
more sensitive PCR (polymerase chain reaction) test, which takes up to 48 hours
to return results, reduced infectiousness by only 58%. When the amount of
testing was the same, the rapid test always reduced infectiousness better than
the slower, more sensitive PCR test.
That's
because about two-thirds of infected people have no symptoms and as they await
their results, they continue to spread the virus.
"This
paper is one of the first to show we should worry less about test sensitivity
and, when it comes to public health, prioritize frequency and turnaround,"
said senior co-author Roy Parker, director of the BioFrontiers Institute and a
Howard Hughes Medical Institute investigator.
The
study also demonstrates the power of frequent testing in shortening the
pandemic and saving lives.
In
one scenario, in which 4% of individuals in a city were already infected, rapid
testing three out of four people every three days reduced the number ultimately
infected by 88% and was "sufficient to drive the epidemic toward
extinction within six weeks."
The
study comes as companies and academic research centers are developing low-cost,
rapid turnaround tests that could be deployed in large public settings or
commercialized for do-it-yourself use.
Sensitivity
levels vary widely. Antigen tests require a relatively high viral load -- about
1,000 times as much virus compared to the PCR test -- to detect an infection.
Another test, known as RT-lamp (reverse transcription loop-mediated isothermal
amplification), can detect the virus at around 100 times as much virus compared
to the PCR. The benchmark PCR test requires as little as 5,000 to 10,000 viral
RNA copies per milliliter of sample, meaning it can catch the virus very early
or very late.
In
the past, federal regulators and the public have been reluctant to embrace
rapid tests out of concern that they may miss cases early in infection. But, in
reality, an infected person can go from 5,000 particles to 1 million viral RNA
copies in 18 to 24 hours, said Parker.
"There
is a very short window, early in infection, in which the PCR will detect the
virus but something like an antigen or LAMP test won't," Parker said.
And
during that time, the person often isn't contagious, he said.
"These
rapid tests are contagiousness tests," said senior co-author Dr. Michael
Mina, an assistant professor of epidemiology at the Harvard T.H. Chan School of
Public Health. "They are extremely effective in detecting COVID-19 when
people are contagious."
They
are also affordable, he added. The rapid tests can cost as little as $1 each
and return results in 15 minutes. Some PCR tests can take several days.
Mina
envisions a day when the government sends simple, cheap DIY tests to every home.
Even if half of Americans tested themselves weekly and self-isolated if
positive, the result would be profound, he said.
"Within
a few weeks we could see this outbreak going from huge numbers of cases to very
manageable levels," Mina said.
Rapid
testing could also be the key to breathing life back into former super spreader
threats like football stadiums, concert venues and airports, with patrons
testing themselves on the way in and still wearing masks as a precautionary
measure, Larremore said.
"Less
than .1% of the current cost of this virus would enable frequent testing for
the whole of the U.S. population for a year," said Mina, referencing a
recent Harvard economic analysis.
The
authors say they are heartened to see that several countries have already begun
testing all of their citizens, and hopeful that the new U.S. administration has
named rapid testing as a priority.
"It's
time to shift the mentality around testing from thinking of a COVID test as
something you get when you think you are sick to thinking of it as a vital tool
to break transmission chains and keep the economy open," Larremore said.
