Review prompted by new evidence
The US administration debated and decided to change its advice on masks in recent days. On Tuesday, Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNN that the White House Coronavirus Task Force was discussing the issue.
On Thursday, he indicated the advice would change and Americans would be encouraged to wear masks, saying: “Given the fact that we know that asymptomatic people are clearly transmitting infection, it just makes common sense that it’s not a bad idea to do that.”
On Friday, Surgeon General Adams acknowledged that some would find the change in position confusing, but said it followed new information that infected people without symptoms could be spreading Covid-19.
New data has shown that as many as 25 per cent of those infected had no symptoms, according to the US Centers for Disease Control and Prevention (CDC). That means an infectious person displaying no symptoms and not wearing a mask can infect healthy individuals who are also unprotected.
The novel coronavirus is believed to spread through tiny viral particles and droplets which can stay on surfaces or hang briefly in the air after a person coughs, sneezes or touches an object. A healthy person may get infected if those viral droplets enter his mouth, nose or eyes, if he touches his face, or comes into close contact with a Covid-19 patient.
A surgical mask can block splashes and large-particle droplets, but does not filter very small particles transmitted when a person coughs or sneezes and during certain medical procedures. The tightfitting ultra-high infiltration N95 mask used by health professionals is effective in blocking at least 95 per cent of tiny airborne particles.
The WHO has maintained that the virus is “primarily transmitted between people through respiratory droplets and contact routes” such as coughing and sneezing. Some recent studies suggest that infected droplets can travel further than 2 metres when a sick person coughs or sneezes, prompting calls to extend the use of masks.
Professor Yuen Kwok-yung, the University of Hong Kong’s (HKU) top microbiologist and an early proponent of wearing masks in the city, has described the case of a seven-year-old girl who resisted Covid-19 while her family members fell sick.
In a study published in the medical journal Lancet, he said the family of six travelled to Wuhan, the epicentre of China’s Covid-19 outbreak, and the girl was the only one in the family who did not contract the virus. The reason: she wore masks throughout their trip.
Dr Leung Chi-chiu, chairman of the advisory committee on communicable diseases at the Hong Kong Medical Association, said the universal use of masks was vital in reducing the spread of the virus.
“Transmission from asymptomatic infected individuals has been documented for Covid-19, and viral load is particularly high at the early stage of the disease. Masking, as a public health intervention, will probably intercept the transmission link,” he said.
There have been some concerns about the improper use of masks, and whether they give users a false sense of security, causing them to ignore critical hand-hygiene advice.
However, HKU’s Benjamin Cowling, professor of epidemiology and biostatistics, said: “I am not clear why there is a different standard applied to use in the community, that face masks are really, really an important part of protection of medical workers – I agree with that – but somehow not effective at all in the general community because people don’t know how to wear masks properly.
“If that’s really the case, the solution is to have a public education campaign, not to avoid recommending the use of masks.”
There are other benefits in more widespread use of masks. Shan Soe-lin, a lecturer in public health at Yale University, said the sight of everyone in masks can stimulate behavioural change by signalling the seriousness of the pandemic and the need for protection.
“It reduces stigma and encourages others to wear masks, which further amplifies the collective benefits,” she added. “People touch their faces an average of once every 2.5 minutes, which is a very hard, if not impossible habit to break. Covering your face keeps your hands away from your nose and mouth.”