What we know now about the Covid-19 ‘lifespan’

The virus can be airborne and live on surfaces for weeks - but person-to-person transmission is still the leading cause of new infections

• 

  A man wearing face masks to protect against the spread of the new coronavirus walk at pier of Yokohama, near Tokyo. AP Photo

• 

  Iraqi Christians attend a Sunday service in one of the Chaldean churches that reopened after months of closure due to the coronavirus disease outbreak, in Baghdad, Iraq. REUTERS

• 

  Yellow and black tape marks an area on the floor for teachers to be socially distanced from students in class at Melba Secondary College in Melbourne, Australia. All primary and high school students in Melbourne are able to return to their classrooms as of today, as part of Victoria's second step in the government's roadmap to reopening. Victoria's coronavirus restrictions were eased slightly across Melbourne from Monday 28 September. Metropolitan Melbourne has been subject to Stage 4 restrictions since 2 August 2020 in response to the re-emergence of COVID-19 in the community. Getty Images

• 

  A 'Covid-19 Awareness Project' volunteer measures the body temperature to check on a patient infected with leprosy as part of a general health checkup for all inmates at the Gandhi Leprosy Seva Sangh rehabilitation centre, in Ahmedabad. AFP

• 

  Los Angeles Lakers fans celebrate their team winning the 2020 NBA Championship against the Miami Heat, during the outbreak of Coronavirus disease in Los Angeles, California, U.S. REUTERS

• 

  People attend a 'No Mask' protest rally 'Marcia della Liberazione' in Rome, Italy. The sit-in protest action is held against mandatory usage of face masks in public and in general against the government's management of the coronavirus Covid19 pandemic. EPA

• 

  A man wearing a mask walks outside Seoul City Hall in Seoul, South Korea. The South Korean government decided to lower its social distancing guidelines to the lowest level on 11 October amid a noticeable slowdown in new coronavirus cases. EPA

• 

  Officials wearing personal protective equipments (PPE) pray for the bodies of people who died due to the coronavirus disease at a crematorium in Bangli, Bali, Indonesia. REUTERS

• 

  A Garuda Indonesia Boeing 373-800 NG with a new face mask design as part of a campaign to promote the wearing of face masks amid the Covid-19 coronavirus, is parked at the airport in Tangerang. AFP

• 

  A COVID-19-infected patient is seen at the Intensive Care Unit, in the Emilio Ribas hospital in Sao Paulo, Brazil. On October 10, Brazil passed the bleak marker of 150,000 deaths from Covid-19, the health ministry said, as the rate of coronavirus infections continues to slow in the South American country. AFP

• 

  A security guard wearing a facemask as a preventive measure against the Covid-19 coronavirus is pictured in Mumbai. India's coronavirus cases surged past seven million on October 11, taking it ever closer to overtaking the United States as the world's most infected country. AFP

• 

  Dr. Moatasem Muheisen, right and his staff throw a birthday party for their colleague Dr. Abdulbaset Zieneddin, 42, second right, in a COVID-19 testing center, at the Ramallah Recreational Complex, in the West Bank city of Ramallah. The Palestinian ministry of health transformed a sports facility into a COVID-19 testing center where health care workers provide support for residents who come forward for a consultation or a COVID-19 test during the pandemic. AP Photo

• 

  Medical staff discuss data on a screen at the coronavirus ward of the Rambam Health Care Campus, initially built as an underground medical facility before being converted to a car park, then to a center to receive patients as COVID-19 cases surge, in the northern Israeli city of Haifa. Israel opened a new coronavirus treatment facility co-run by the army's medical corps, an unprecedented move for the military unit, aimed at bolstering an embattled healthcare system. The Jewish state currently has one of the world's highest daily coronavirus infection rates per capita, with the number of seriously ill patients steadily rising. The army-backed unit at the Rambam Hospital in the northern city of Haifa includes a control room where patients are monitored via video and an underground coronavirus ward that used to be a car park. AFP

Seven months on from when the coronavirus outbreak was officially declared a pandemic, scientists are still unveiling new – and sometimes surprising – findings about how the pathogen might spread.

In the latest research to hit the headlines, scientists in Australia found that virus particles on surfaces could potentially remain infective for four weeks.

Contrasting with earlier findings, suggesting the virus could not remain viable on surfaces for more than a few days, this finding came soon after new guidance highlighted the possible risk of airborne transmission.

And last week, the US Centres for Disease Control said tiny virus-containing particles remaining suspended in the air after being released by infectious people could pass on the pathogen.

The researchers in Australia, who were from the country’s Commonwealth Scientific and Industrial Research Organisation, found the virus could remain viable for 28 days on smooth surfaces such as plastic banknotes and mobile phone screens.

I don't think overall it changes anything. It just re-enforces the, 'Wash your hands,' message

While the work involved samples that were being kept in the dark, when light is known to harm the virus, the scientists said their results could be relevant to efforts to prevent the coronavirus from spreading.

“These findings demonstrate SARS-CoV-2 can remain infectious for significantly longer time periods than generally considered possible,” they wrote.

However, not all experts view laboratory studies of this kind as being helpful in indicating real-world transmission risks. Ian Jones, a professor of virology at the University of Reading in the UK, said data about what “could” happen with the virus was not useful.

"Lab conditions are idealised, in the dark and constant temperature in this case, and it is far more likely temperature would vary, light would vary or wiping would occur," he told The National.

“So I don't think overall it changes anything. It just re-enforces the ‘wash your hands’ message but should not detract from the fact that the majority transmission is by aerosol and that is where the most focus for useful barriers to infection should be.”

Numerous other studies have found that coronavirus samples on surfaces become harmless after much shorter periods of time. One found that it was no longer infectious after three days on plastic or steel, after only 24 hours on cardboard, and after a mere four hours on copper.

The researchers in Australia found the number of infectious virus kept on a surface at 20 degrees Celsius halved every 1.7 to 2.7 days, showing that while some particles could live for 28 days, by that time only a fraction were viable. At 40°C, the number remaining infectious halved every few hours.

The coronavirus is “a pretty tough virus in all sorts of ways”, according to David Taylor, a professor emeritus of pharmaceutical and public health policy at University College London. However, he said surface transmission of the virus was not likely to be the main mode of spread.

“It makes sense to have clean surfaces, but what we don’t know is how much virus that’s on a surface for days … is likely to be a source of infection,” said Prof Taylor.

The Centres for Disease Control’s warning that airborne transmission was possible concerns tiny particles that linger in the air for as long as several hours, as opposed to larger respiratory droplets that a person exhales and that quickly fall to the ground or land on surfaces or other people.

The organisation said most spread of SARS-CoV-2, as the new virus is officially known, were through such larger droplets causing infection “within a short range” of less than 1.8 metres.

Airborne transmission is believed to be uncommon and would normally involve an infectious person producing tiny droplets in an enclosed space for a long time, such as when exercising.

“There is no evidence of efficient spread (i.e., routine, rapid spread) to people far away or who enter a space hours after an infectious person was there,” the CDC guidance states.

Prof Taylor agreed that larger droplets rather than tiny airborne particles were more likely to be involved in the pathogen’s transmission.

“Droplets fall to the ground quicker or they are sprayed on to the lips and nose. That’s the biggest transmission risk, I believe,” he said.