One of the most common questions people ask FactCheck is how long the coronavirus can survive on surfaces and in the air while it is still infectious.

A widely published story last week quoted a US government Centers for Disease Control and Prevention (CDC) publication which said that parts of SARS-CoV-2, the virus which causes the disease COVID-19, were found on the Diamond Princess cruise ship after 17 days:

“SARS-CoV-2 RNA was identified on a variety of surfaces in cabins of both symptomatic and asymptomatic infected passengers up to 17 days after cabins were vacated on the Diamond Princess but before disinfection procedures had been conducted…”

This caused some anxiety on social media, as people believed the virus could last anywhere for more than two weeks. But the next sentence of the publication is also important:

“Although these data cannot be used to determine whether transmission occurred from contaminated surfaces, further study of fomite transmission of SARS-CoV-2 aboard cruise ships is warranted.”

This means that more research is needed to determine whether what they found 17 days later can actually result in infection.

Experts commenting on this to the Science Media Centre pointed out that it was genetic material called RNA which was detected, as opposed to the whole functional virus, which we know can definitely infect people. There is currently no evidence to suggest these types of genetic traces can cause infection.

Rather than looking at how long traces of the virus can survive, a study published in the New England Journal of Medicine on 17 March looked at how long the functional, infectious virus can persist in five conditions – in aerosols (most similar to air), and on plastic, stainless steel, copper, and cardboard.

This study found that the virus did not survive in any condition tested for longer than three days.

On certain surfaces, such as copper, the virus survived for hours rather than days. No functional virus was found on cardboard after 24 hours.

The virus survived the longest – up to three days – on plastic and stainless steel.

In aerosol form – tiny particles floating in the air – the virus survived for three hours. But experts commenting on the study pointed out that there are limits to what this tells us: the experiment was carried out using a nebuliser to produce the aerosol, whereas typical human coughs produce large droplets which would fall to a surface more quickly than nebuliser aerosol.

More research with COVID-19 patients is needed to find the extent to which small particles are produced by coughing.

Lastly, the study found that the infectivity of the virus samples decreased on surfaces over time – so even if a virus is present on a surface after three days, it is less likely to give infection than the surface was after one hour.

The findings mirrored those found about the behaviour of other coronaviruses such as SARS, and didn’t change the assumptions about COVID-19 that had been made before the publication.

Experts interpreting the findings suggested that leaving surfaces for four days would be maximally cautious for anyone worried.

The UK government recommends washing surfaces with disinfectants as they can kill the virus within minutes – and to wash hands regularly.