Khaberni - In a scientific attempt to uncover the secrets of contagion transmission, researchers were shocked by unexpected results that overturned their understanding of the mechanism of influenza virus spread.
Scientists conducted an experiment that had shocking results: they placed a group of volunteers for several days in a small hotel room with people actually infected with the flu, they played group games, shared items, and exercised together under conditions designed to promote the spread of the virus, yet no influenza cases were documented among them! What could be the reason for this?
This unexpected outcome arose from a well-designed study aiming to answer a fundamental question: How does the influenza virus actually spread?
It is known that the influenza virus is transmitted through airborne particles or microscopic droplets that are emitted when coughing, sneezing, or even during normal breathing, and may also move from one person to another via contaminated surfaces such as door handles or phones.
The efficiency of virus spread depends on several factors, including the amount of virus released by the infected person, the temperature and humidity inside the space, and the proximity of the individuals to each other.
To understand the most influential factors, researchers from the University of Maryland in the US conducted a field experiment on contagion transmission using naturally infected individuals with influenza.
The researchers gathered a group of participants inside a hotel room, where the actually infected individuals, referred to as "donors" in the study, mingled with uninfected volunteers named "recipients". The aim was simple: to verify the possibility of virus transmission under conditions designed to facilitate contagion.
This approach differed from previous studies in which healthy volunteers were intentionally infected with the flu for research purposes, but researchers in this study specifically used naturally infected people in an attempt to more accurately represent how the disease spreads outside the lab.
Two versions of the experiment were executed: in the first, one donor shared the room with eight recipients, and in the second, 4 donors shared it with 3 recipients. The donors' ages ranged between 20 and 22 years, while the recipients' ages varied between 25 and 45 years.
The researchers adjusted the room's temperature and humidity at levels believed to promote influenza transmission, with temperatures ranging between 22 to 25 degrees Celsius, and humidity between 20% and 45%. They also closed any non-sealed ventilation paths such as windows and doors and leaks in air conditioning units before isolating the participants, aiming to create an environment with low ventilation and poor air quality.
Over a period that lasted from three to seven days, participants spent long hours together in confined space, and their activities included playing card games up close, participating in dance or yoga sessions, and sharing the use of communal items such as pens, microphones, and tablets.
Researchers monitored contagion transmission by measuring virus levels in exhaled air and saliva and swabs of the donors' mouths, and they also examined shared tools and room air for viral particles, as well as monitoring disease symptoms among participants, such as coughing, sneezing, headaches, and other common flu signs.
Several samples from the donors confirmed active influenza infection, yet no positive results were registered among the recipients; and while some reported mild symptoms such as headaches, there was no clear evidence of disease infection.
The researchers proposed three main explanations for the lack of contagion: the low amount of virus emitted by the donors, the presence of partial immunity among the recipients, and the air circulation pattern inside the room.
Although it is commonly believed that children play a major role in spreading influenza, this study was limited to adults, and it was noted that adult donors emitted relatively limited amounts of virus, which might be attributed to virus strains, participants' ages, or the scarcity of visible symptoms. A clear reduction in coughing and sneezing rates was also observed, which confined the amount of virus spread in the air.
On the other hand, the recipients might be less susceptible to the virus, as they all went through multiple flu seasons, and some had been vaccinated in previous years, while one of them was vaccinated in the current season. It is likely that this previous exposure contributed to developing a level of immunity against the virus.
Despite setting temperature and humidity levels supportive of contagion, the high rate of air circulation caused by fans likely led to dispersing and diluting the air masses carrying the virus, reducing the amount of virus inhaled.
These findings collectively suggest that coughing and sneezing are among the primary factors in spreading influenza, especially among individuals who emit large quantities of the virus, sometimes referred to as "super spreaders". It also appears that immunity among those exposed to the infection and indoor air movement play a crucial role.
This study does not imply that influenza is a non-serious or hard-to-transmit disease; it records annually millions, possibly billions, of cases worldwide, with strong evidence that airborne transmission plays a pivotal role, but it clarifies that the conditions for contagion spread are more complex than just being in the same place with an infected person.
Not all individuals emit the virus in the same amount, nor does everyone have the same susceptibility, and airborne transmission is more likely during coughing and sneezing, so experts recommend isolating infected individuals as much as possible and wearing well-fitted masks to reduce the virus emission in the air. Moreover, good ventilation and air circulation are important factors, especially in small, poorly ventilated spaces.
When in doubt, it is safer to assume the possibility of contagion or having already contracted it, along with adhering to public health guidelines such as vaccination and using masks when needed.
