When I was a junior doctor I spent time working in both respiratory medicine and infectious diseases, and so I know a little bit about respiratory viruses. Coronaviruses are just that, a family of viruses which cause respiratory tract infections, ranging from very mild to fatal. The common cold is often caused by a coronavirus, as are the more serious infections such as SARS and MERS.
Infection passes from someone who is infected, to someone who is not, when the infected person breathes, coughs or sneezes out droplets which contain the virus. To become infected, a lot of the virus from these droplets has to get into the respiratory tract of the non-infected person, via the nose and mouth. The other possible mode of transmission is via the eyes, as the tear ducts connect the eyes to the nasal cavity.
Almost all the information around not spreading the virus, that I have seen in New Zealand and other Western countries has been focused on handwashing in order to stop the transmission of the virus that could occur when people touch surfaces that have infected droplets on them, and then touch their nose, mouth or eyes.
Until a few days ago (I am writing this over the Easter weekend) not only were authorities such as the World Health Organisation (WHO) and governments not recommending the use of masks by the public, but they were saying that they could do more harm than good, and that handwashing and social distancing were important. They also gave out the mixed message that masks were more harmful than beneficial…..but that there was a shortage of masks and healthcare workers should be the priority.
As discussed, respiratory viruses are predominantly spread by breathing in droplets containing virus, not by touching infected items as predominantly occurs with, for example, norovirus. The best study (Zhang) I have seen on this, estimates that less than 5% of influenza is spread by touching, and I would argue that it is less than this.
Masks provide two physical barriers that stop the infected droplets being transmitted - the masks worn by the infected people and the masks worn by those not infected. This is excellent, if not perfect, prevention. It is true that no clinical studies have proven that masks prevent the transmission of respiratory viruses. Such studies would be almost impossible to undertake, for both practical and ethical reasons. It is not a surprise to me that in mask-wearing Asian countries such as South Korea, Hong Kong and Singapore, that the number of coronavirus infections and deaths are much lower than in the USA and Europe where few people wear masks.
There is a shortage of masks in non-Asian countries, and, reading between the lines, this may be why authorities in those countries are not recommending them for the public. In some countries there are not even enough for healthcare workers. The good news though is that even homemade masks, should provide almost as good protection as surgical masks and there are many websites which show people how to make them.
1. Zhang, N., & Li, Y. (2018). Transmission of influenza A in a student office based on realistic person-to-person contact and surface touch behaviour. International journal of environmental research and public health, 15(8), 1699.