Coronavirus Spreads More Easily in Certain Environments

09 June, 2020
One group of researchers, led by Dr. Akiko Iwasaki, noted that coronavirus spreads more easily in certain environments. In particular, cold, dry air creates conditions that increase transmission and decrease the body's ability to respond.

Recent research in the United States indicated that it’s likely that coronavirus spreads more easily in certain environments. In contrast to what has been suggested in recent weeks, a crucial factor in the spread of COVID-19 is not climate, but the humidity.

If it’s proven that humidity is a relevant factor in the spread of the epidemic, then we could expect that there will be a significant decrease in cases in the northern hemisphere with the arrival of spring. However, the change in season alone wouldn’t be enough.

According to the study mentioned above, the crucial factor would operate within households. Since coronavirus spreads more easily in some environments than in others, the right thing to do would be to increase the humidity inside houses and buildings as a measure to reduce infections.

Coronavirus spreads more easily in certain environments

Coronavirus spreads more easily in certain environments.
The relationship between environmental conditions and the spread of the coronavirus is currently being studied.

The recent study by Yale University concluded coronavirus spreads more easily in certain environments. In particular, cold, dry environments are ideal for the spread of infection. On the other hand, warm and humid environments could help to slow down its spread.

Although there are still many unresolved questions, it’s clear to most scientists that cold, dry winter air favors SARS-CoV-2, the virus that causes COVID-19. This type of environment helps the infection spread more quickly between people.

Immunobiologist Akiko Iwasaki, the study’s director, said that we’ve known for hundreds of years that respiratory illnesses increase in winter and decrease with the arrival of spring and summer. These days we know that this is mainly because cold and dry air encourages the spread of a virus.

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Humidity affects whether coronavirus spreads more easily

Yale scientists noted that when the air is cold and dry outside, the heat increases inside the homes. This leads to the relative humidity inside a house or building reducing by about 20%. This then makes these environments conducive to the spread of the coronavirus.

To make matters worse, these hot, dry environments aren’t at all favorable for the proper functioning of the airways. Such environments mean that our cilia lose their ability to function well. The cilia are a type of hair that covers the airways and helps to expel viral particles.

Also, in hot, dry environments, the immune system’s ability to respond to viruses and bacteria is suppressed. Therefore, the researchers conclude that such environments create a simultaneous risk factor on three different fronts.

Experiments and other data

A woman with a cold.
Experts believe that, in low humidity environments, viruses spread more easily.

The Yale researchers cited lab tests conducted on mice. They found that in low-humidity environments, rodents infected with respiratory viruses were more likely to spread the virus to others.

It was also found that mice living in environments with 50% relative humidity were able to generate more robust immune responses and eventually expel the inhaled viruses. A similar effect occurs in environments with a humidity of between 40 and 60 %.

On the other hand, they pointed out that in tropical countries (where there’s a high relative humidity in the environment), the droplets expelled by infected people may remain on surfaces longer than usual. If you add to this the lack of ventilation and overcrowding, then the advantages of ambient humidity are lost.

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Preventive measures

Scientists have been emphatic in stating that these findings only apply to the transmission of the disease through the droplets that an infected person expels when speaking, coughing or sneezing. Because of this, they advise us to take two measures.

The first of these is to use humidifiers in homes during the winter. This could help reduce the spread of the virus. However, this must be accompanied by sufficient ventilation and an absence of overcrowding. If not, then this measure won’t be effective.

However, it’s important to understand that humidity alone won’t prevent infection. At any time of the year, the virus can be transmitted through close contact, and through surfaces where the virus is present. Therefore, social distancing and frequent hand washing will always be important.

  • Caparó, F. L., & Sara, J. C. D. C. (2020). Coronavirus y las amenazas a la salud mundial. Horizonte Médico (Lima), 20(1), 4-5.
  • Moriyama, M., Hugentobler, W. J., & Iwasaki, A. (2020). Seasonality of Respiratory Viral Infections. Annual Review of Virology. https://doi.org/10.1146/annurev-virology-012420-022445
  • Conseleria de Salut – Direcció General de Salut Pública i Participació. (2020). CORONAVIRUS COVID-19. Retrieved from http://www.caib.es/sites/coronavirus/es/portada/#