Vaccination The third dose dilemma
Future These are the possible scenarios for the post-pandemic world
Like SARS-CoV-2, most respiratory viruses, such as influenza or colds, are transmitted primarily through the air, through
aerosols
.
Most respiratory viral infections, such as colds and flu, are spread through the air through aerosols, which can accumulate in poorly ventilated indoor spaces and remain there for hours. It is the same that has been shown with the disease caused by SARS-CoV-2, covid-19, and that also occurs with other coronaviruses (MERS-Cov, SARS-CoV). This is the main conclusion of a scientific review carried out by an international team of specialists from various disciplines and just published in the journal
Science
.
"All or almost all respiratory viruses are transmitted like Covid-19: mostly, or in part, through the air. The World Health Organization (WHO) argued that SARS-CoV-2 was only transmitted by droplets or surfaces, and over time we have learned that this
was a mistake
and that the vast majority of transmission occurs by inhaling aerosols that come out of some infected people.
The transmission by droplets or surface is not important, it is not what is causing the pandemic.
The WHO resisted admitting it for more than a year, until on April 30 it recognized that route of transmission and its importance, and on May 7 the CDC [Centers for Disease Control and Prevention of the United States] did it, "he says. one of the review authors, José Luis Jiménez, Professor of Chemistry at the University of Colorado, Boulder.
Professor Jiménez is one of the leading aerosol experts in the international arena.
It has fought the idea that SARS-CoV-2 spreads mainly through droplets that infected individuals produce by coughing and sneezing and impacting another person directly or by touching surfaces contaminated by these droplets.
A pandemic and an intense global scientific effort have been necessary to
dismantle that dogma
, but finally, it has been achieved. With this review of scientific evidence, the researchers provide the data that support the importance of the route through the air for almost all respiratory viruses, something that has not yet been officially collected by the WHO or the CDC, warns Jiménez.
"In the field of epidemiology and infectious diseases there is a dogma that the diseases that are transmitted through the air are mainly tuberculosis, measles and chicken pox", while the rest are spread by drops and surfaces. "The dogma comes from 1910, from researcher Charles Chapin, who became president of the American Public Health Association, and
he really established it without evidence
."
The deeply ingrained concept in the scientific community explains that transmission by inhalation of virus-laden aerosols has long been underestimated.
"
It is time to review the conventional paradigms
and implement measures against aerosols to protect the population against this route of transmission," says Chia C. Wang, director of the Center for Scientific Research on Aerosols and physical chemistry at the National University Sun Yat-sen, Taiwan, who led the review.
Size Matters
Aerosols are pellets of saliva and respiratory fluid, similar to droplets, but much smaller.
They are less than 100 microns (µm), and most do not even exceed 5 µm;
they are expelled by breathing, speaking, singing, screaming, coughing, and sneezing.
Unlike droplets, they do not fall immediately, but can remain floating in the air for hours and be inhaled.
"Most of the aerosols produced by respiratory activities are smaller than 5 µm, which allows them to penetrate deep into the bronchiolar and alveolar regions and settle there. Studies indicate that viruses are more present in aerosols of less than 5 µm", explains another of the study's authors, Josué Sznitman, a pulmonary physiologist at the Israel Institute of Technology in Haifa.
Measures to control 'virosols'
Not all those infected with SARS-CoV-2 emit virus-laden aerosols uniformly.
"There is great variability among infected people: some do not infect anything", Jiménez clarifies, as it will depend on the viral load and physiological reasons, or vocalization, for example, if it is sung or shouted.
The universal use of the mask is an effective and inexpensive way to block them, according to the review.
However,
more barriers against the virus must be used
.
"It is unlikely that a single strategy is strong enough to eliminate the transmission of emerging variants of SARS-CoV-2", considers the also author of the article Seema S. Lakdawala, virologist at the University of Pittsburgh.
Good ventilation and filtration are therefore essential to prevent recirculation and help reduce airborne transmission of "virosols", virus-laden aerosols. Jiménez highlights the control of CO2 with portable meters, to verify that the ventilation is carried out correctly; if you can't ventilate well, filter the air, which can be helped by
HEPA
[High Efficiency Particulate Filtering]
purifiers
. Instead, the expert flatly rejects systems that try to kill the virus, but leave it suspended in the air, such as those that use ions, photocatalysis, hydroxyl, ozone, bleach, hypochlorous acid, among others. "In some cases UV rays work, but if done right, it tends to be more expensive than filtering the air."
The delta variant, more risk in the air
Studies indicate that the delta variant of SARS-CoV-2 is almost as contagious as chickenpox, but there is nothing to suggest that it is transmitted differently.
Its main route of transmission, as far as is known, is also by air.
Other factors such as a high viral load intervene in this greater capacity for contagion
- "people infected by the delta variant can have up to a thousand times more load" -
, says Jiménez - or variations in the spicule of the virus, which favor interaction with the receptor for entry into the human cell.
To these factors is added a possible reduction in the period from when it contracts until it becomes infective, from about five days with the original strain at three.
With the adult population in the process of completing the vaccination, one of the current concerns in Spain is how going back to school will affect the evolution of the pandemic.
The vaccine in adolescents can help contain it, but those under 12 years of age will face a situation more conducive to contagion.
Outdoor classes;
adequate ventilation;
masks - "but not just anyone: they filter well and fit without leaving gaps" -;
keep distance;
filter the air;
facilitating online classes for immunosuppressed children or those at special risk are measures that Jiménez lists and that
"should be taken seriously"
by the authorities, especially now that science has made it clear where the virus reaches us.
According to the criteria of The Trust Project
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