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By Roger Highfield on

Virus on hands and surfaces spreads COVID-19 in the home

Roger Highfield, Science Director, talks to Ajit Lalvani of Imperial College London about the first detailed study of how the virus is transmitted at home, which underlines the importance of handwashing and hygiene. 

The first evidence for transmission of SARS-CoV-2 via people’s hands and frequently-touched surfaces at home, where most transmission of the disease occurs, is published today by an Imperial College London scientist who conducted studies of COVID19 outbreaks in forensic detail. 

The findings, which complement other studies on how the disease is also transmitted through air by airborne aerosols, underline the importance of frequent handwashing, regular disinfection of surfaces and physical distancing to curb the spread of COVID-19.

The research was conducted by Science Museum Group Trustee Prof Ajit Lalvani, Chair of Infectious Diseases, and Director of the National Institute for Health Research’s Health Protection Research Unit in Respiratory Infections, at Imperial College London.

The study published in the journal The Lancet Microbe was, he said, a “Herculean logistical undertaking” because it was carried out in 279 households in London during the alpha and pre-alpha waves, at the height of the pandemic, and around a year before the distribution of an effective vaccine, which is recounted in the Science Museum’s Injecting Hope exhibition.

Professor Lalvani, who himself fell ill with the disease in the first wave, said: “There’s no doubt that if you have COVID-19 you’re emitting the virus into the air as micro-aerosols as well as large droplets that land on your hands and the surfaces around you. What hasn’t been shown, until now, is that the presence of the virus on people’s hands or household surfaces predicts transmission to contacts.”

“Our real-life study in London households provides the first empiric evidence to show that the presence of SARS-CoV-2 on people’s hands and surfaces contributes significantly to spread of COVID-19,” he said, adding that because they did not systematically sample household air, “we cannot rule out airborne transmission occurring in parallel.”  To date, there is no detailed evidence of the relative contribution of these transmission routes to the spread of COVID-19, he added.

The first study of its kind – by researchers from Imperial College London, the UK Health Security Agency, and the University of Oxford – prospectively recruited 414 ‘susceptible household contacts’, people living in the same households as 279 newly diagnosed primary cases between 1st August 2020 and 31st March 2021. This was early in the pandemic when few had been vaccinated, or previously infected, so the majority were not immune to the disease and susceptible to infection.

All the people infected individuals came into contact with were regularly tested for SARS-CoV-2 infection by nose and throat swabs, and the Imperial team also took swabs from primary cases’ and contacts’ hands as well as frequently touched surfaces in communal areas, such as fridge-door and kettle handles, taps and so on, hunting for SARS-CoV-2 genetic material and counting the number of virus particles.

Nieves Derqui, first author of the study, also from Imperial College London, said: “In houses in which we found the virus on surfaces and the hands of participants, infection among contacts, and thus transmission, was significantly higher.”

If the virus was present on frequently-touched surfaces in the household, for example, contacts were 3.8 times more likely to have detectable virus on their hands and 1.7 times more likely to be infected. In a follow up study of 25 of the primary cases, analysing the virus through its genetic makeup, or sequence, they found the same strain of virus in their respective contacts.

Booster vaccinations are crucial to prevent severe disease and hospitalisation but do not effectively prevent transmission of SARS-CoV-2, said Prof Lalvani, adding: “Our new understanding of the pathways of household transmission now enables us to prioritise simple risk-free measures to interrupt spread of the virus.

Our data strongly suggest that as well as frequent hand-washing, decontamination of frequently-touched surfaces should prevent transmission. Wearing face-masks is also important, as it interrupts not only airborne spread but also spread via surfaces and hands as face-masks prevent contaminated hands touching the nose and mouth through which the virus can enter the body.”