Doctors explained the cases of absence of flu symptoms when in contact with an infected person

Researchers from the University of Maryland have found that with the active use of ventilation and heating systems, the flu may not be transmitted from person to person in the same room. This is reported in an article published in the journal PLOS Pathogens.

The project involved 11 healthy recipients and five students with confirmed influenza. For two weeks they lived together on an isolated floor of the hotel. During the experiment, the participants supported such ordinary everyday interactions as communication, joint performance of household chores. As a result, none of the healthy participants showed flu symptoms.

Among the possible reasons for the absence of a case of transmission of the disease, experts identified a rare cough in a flu carrier, seasonal fluctuations in viral aerosol release, as well as more pronounced cross-immunity in healthy participants, which had accumulated over the years of vaccinations and previous infections. In addition, the concentrated clouds of exhaled air were quickly destroyed by its high circulation in the room.

According to the researchers, although it has now been proven that the infectious virus spreads through coughing and normal breathing, the relative importance of the various transmission routes (inhalation, droplets, contact) has not been fully understood.

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An additional factor was the pre-existing immune protection of the recipients. Despite the low titers of HAI antibodies, they showed higher levels of binding antibodies, indicating partial protection. The average age of the participants, about 36 years old, could also reduce susceptibility to infection.

The temperature and humidity in the experiment were in a range favorable for the survival and transmission of the virus, so they do not explain the absence of infection. However, the high air mixing rate provided by ventilation systems could reduce the short-term effects of concentrated aerosol jets.

The authors concluded that the transmission of seasonal influenza is probably mainly associated with more symptomatic cases of coughing and episodes of "super-release" of the virus. It is also emphasized that the lack of transmission from mild cases of influenza to healthy adults in conditions of intense air mixing highlights the complexity of the mechanisms of virus spread and the need for further research to better control seasonal epidemics.

Ophthalmologist, ophthalmic surgeon at SM Clinic, PhD Svetlana Mirgorodskaya, in an interview with Izvestia on December 22, 2025, spoke about the ability of influenza A to affect vision after recovery. According to her, first of all, this may be due to a post-viral immune reaction. Nikolai Kryuchkov, an expert on public health, an immunologist, Candidate of medical Sciences, in turn, called for immediate medical attention in case of visual impairment after the flu.

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