Volunteers spent several days in a small hotel room with people who had the flu, where they played games, shared things and exercised together, in conditions designed to facilitate the transmission of the virus.
However, no one became infected. This study, conducted at the University of Maryland in the United States, aimed to answer a key question: How does influenza actually spread?
The virus is known to spread through aerosols from coughing, sneezing, or even breathing, and can also be transmitted via contaminated surfaces such as doorknobs or phones. Its transmission efficiency depends on the viral load, temperature, humidity, and proximity of individuals.
To simulate real-world scenarios, researchers paired naturally infected "donors" with uninfected volunteers, dubbed "recipients," in a tightly ventilated room. Two versions of the experiment were conducted: in the first, one donor participated with eight recipients, and in the second, four donors with three recipients. The donors were between 20 and 22 years old, and the recipients between 25 and 45. The researchers maintained a temperature between 22 and 25 degrees Celsius and humidity between 20% and 45%, while intentionally reducing ventilation.
For three to seven days, participants spent hours together in a room, playing card games, taking dance or yoga classes, and sharing items such as pens, microphones, and tablets. Researchers monitored transmission by measuring the virus in exhaled breath, saliva, and oral swabs, and by examining the air and shared objects.
Despite confirmation of active infections in the donors, none of the recipients contracted influenza. Some recipients reported mild symptoms such as headaches, but there was no evidence of actual infection.
Researchers believe the reason lies in three main factors:
1. The amount of virus excreted by the donors was low, possibly due to their age, lack of symptoms, or the strain of the virus.
2. Recipients may have partial immunity, as most of them lived through previous flu seasons, and many of them received multiple vaccinations.
3. Air movement in the room, as the fans dispersed the air carrying viruses, thus reducing the amount of virus inhaled.
The study indicates that coughing and sneezing are the main drivers of influenza spread, especially from people who expel large amounts of the virus, while individual immunity and air movement in enclosed spaces play a crucial role.
The study also confirms that influenza remains highly contagious globally, and that sharing a room with an infected person is not enough to transmit the virus; the amount of virus shed by infected individuals varies, as does the degree of exposure to the virus. Therefore, those infected are advised to self-isolate, wear a mask, and ensure good ventilation in enclosed spaces.
The report was prepared by Conor Meehan, Associate Professor of Microbial Bioinformatics, Nottingham Trent University.
