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Research briefs: Young children spread COVID-19, study says

Children, dry air, small droplets all focus of new findings on the agents of transmission

Pediatric COVID-19 vaccine 1.jpg
Children receive a pediatric two dose series of the Pfizer COVID-19 vaccine at Tri-County Health Care as of November 2021. A parent must be present in order for a child to receive the vaccine. Contributed / Tri-County Health Care

ROCHESTER, Minn. -- In findings of interest to the effort to vaccinate children under 12 for COVID-19, a team of researchers from the Fujian Provincial Hospital in China have determined unvaccinated children under 12 were primary drivers of an outbreak in September and October of this year.

The study, published in preprint form on the website earlier this month -- and not subject to peer review at this time -- investigated the course of illness for 226 positively diagnosed COVID-19 patients.

The group studied included 77 unvaccinated children under 12, and 149 mostly vaccinated people aged 12 and up.

Noting that those under 12 made had milder fever, less cough and fatigue yet made up over a third of the diagnosed, the authors determined "the delta surge in Putian spread from children in schools to factories, mostly through family contact."

The Chinese researchers described an index case in the province as "a middle-aged male," a person infected during quarantine after entry into China. He then transmitted the virus to his two children.


"The activities of the children in the school spread the virus to their classmates," they reported, "which further extended the transmission to the factories through family contact. All of the cases were epidemiologically or genetically traced back to the first case."

"Children aged (less than) 12 (years of age) may be critical hidden spreaders," the authors concluded, "which indicates an urgent need of vaccination for this particular population."

The authors wrote that if no attention is paid to children with mild symptoms, "they may carry the virus for a longer time and become hidden disseminators of delta virus."

Cases among children in the U.S. have risen by 142,000 or 32% in the last two weeks, according to a statement released Monday, Nov. 22, by the American Academy of Pediatrics.

Modeling data suggests 6-foot distance is insufficient

A cough, researchers have learned, starts out as a downward jet and becomes a floating puff.

Higher loading doses of the delta variant are considered part of its transmissibility, and this makes the distribution of droplets following a cough even more important to understand.

A new computer modeling study in the journal Physics of Fluids explored this directional nature of exhalation via cough in stagnant air conditions.

It learned that the primary energy from a typical cough travels downward and vertically for just over one meter, where large droplets fall to the ground.


But a cloud of small droplets and medium can also remain suspended while moving upwards and outwards for another meter, they found. These particles become subject to randomness of turbulent air flow, showing greater buoyancy as they float in place and spread upward.

Though larger droplets carry more virus, the authors write, smaller ones are easily inhaled, making them a less acknowledged part of transmission that can lead to infection. The study suggest that just 20 seconds after a cough from a distance of one and half meters is enough to cause infection

"Thus, it is unclear if a 2.0 meter (6 foot) distance is safe to be practiced even outdoors," they wrote, "as these droplets may carry a significantly large amount of virus over large distances."

"More today," as physician-scientist Dr. Eric Topol argued of the findings on Twitter, "why the 6-foot rule belongs 6 feet under."

Humid rooms lower spread of COVID-19 virus

Canadian engineers have published a new review of the research on humidity and COVID-19 and its case for the value of a humidifier.

The paper, preprint research presented on the website and not yet subject to peer review, has gleaned from a review of 24 qualifying studies that relative humidity over 60% is associated with decreased virus survival compared with air settings below 40% relative humidity.

The effects of humidity on virus transmission are considered multifactorial, reflecting the fat envelope surrounding a coronavirus particle and the lining of the nose where it lands.

High relative humidity causes virus particles to fall to the ground faster.


"Not only does relative humidity affect viral particles," the authors wrote, "it can also have an impact on the host." In conditions of dry air, it is believed, the body's natural clearance system for the airways functions less efficiently.

"This would render the host more susceptible to respiratory virus infections."

The authors caution that coronaviruses do not all behave the same way in relation to moisture levels in the air.

As proof, they describe how higher humidity causes the MERS-CoV virus to become more infective, meaning that blanket relative humidity recommendations were challenging.

But for limiting the spread of COVID-19, humidity is helpful.

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