Corona virus: indoor infection risk 19 times higher than outside

Corona virus: indoor infection risk 19 times higher than outside

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Why we should move many activities outside

During the coronavirus pandemic, it is particularly important to know where and in which situations the risk of infection is highest. A recent Japanese research study examined the situations in which people became infected with SARS-CoV-2. It was found that the probability of getting infected indoors is around 19 times higher than in the fresh air.

Japanese researchers from the National Instiute of Infectious Disease and the National Institute of Public Health searched for common traits that lead to the transmission of the SARS-CoV-2 coronavirus from one person to one or more other people. It was found that COVID-19 is 18.7 times more likely to be transmitted in a closed environment than in an outdoor environment. The results of the study can be viewed on the preprint server "MedRxiv".

Infectious events

The greatest danger during a pandemic are so-called "superspreading events". This means situations in which an infected person infects many other people with an illness within a short period of time. In the initial phase of the coronavirus pandemic, such incidents occurred, for example, at the carnival in Heinsberg or at the apr├Ęs-ski in Ischgl.

But also in the last days and weeks there have been such events in which numerous people have become infected at once, for example during a celebration in a restaurant in Lower Saxony, during rehearsals of the choir of the Berlin Cathedral Choir or at a Baptist service in Frankfurt.

Interiors as common features

What unites these events? They all took place in closed rooms. This is also underlined by the current study from Japan. The researchers examined the relationships between 110 COVID-19 cases. 27 primary cases infected a total of 83 additional people. A closer look showed that the transmissions mainly took place indoors. In total, there were only 18.7 indoor transmission cases in which one person became infected in an outdoor environment.

Closed rooms increase the risk of infection

The research team believes it is plausible that a closed environment massively increases the risk of infection with COVID-19. The risk of "superspreading events" also increases when infected and non-infected people are together indoors.

Limitations of the study

So far, the study has only been published as a pre-publication on a preprint server. A review by other scientists is still pending before the research work can be published in a recognized journal. The virologist and coronavirus expert Professor Dr. Christian Drosten has already looked at the study and believes the results are "robust and interesting", as he reports in the NDR's coronavirus podcast. (vb)

Author and source information

This text corresponds to the requirements of the medical literature, medical guidelines and current studies and has been checked by medical doctors.

Graduate editor (FH) Volker Blasek


  • Hiroshi Nishiura, Hitoshi Oshitani, Tetsuro Kobayashi, u.a .: Closed environments facilitate secondary transmission of coronavirus disease 2019 (COVID-19), MedRxiv, April 2020,
  • NDR: Coronavirus update with Christian Drosten (43): Shifting life outside (published: May 26th, 2020,

Video: Dr. Joe Schwarcz: Whats the COVID-19 risk outside? (November 2022).