Mask use during COVID-19: A risk adjusted strategy^☆

1.2. High proportion of cases with mild symptom or asymptomatic cases

Another important feature of the COVID-19 is that asymptomatic cases proportion is high. It is estimated approximately 60% of all infections convert from cases with mild symptom or asymptotic cases and might be passing the virus on to others (Qiu, 2020). Of the confirmed cases in Diamond Princess cruise ship, approximately 17.9% of infected people never developed symptoms, leading to high attack rate among cruise ship passengers and crew (Mizumoto et al., 2020). This proportion echoes with the finding of an epidemiological characteristics of COVID-19 close contacts in Ningbo, China that 16.7% of infected cases were asymptomatic (Chen et al., 2020). The proportion of asymptomatic cases was estimated to be 16.38% and 27.56% in Hubei and other provinces in China, respectively (data from China CDC). The transmission rate of undocumented infections, those who undergo mild, limited, or no symptoms and hence go unrecognized, was 55% of documented infections (46%–62%) due to high quantity, and undocumented infections were the infection source of 79% of documented cases (Li et al., 2020), leading to a great public health threat.

1.3. Strong infectivity of SARS-CoV-2

The basic reproductive number (R₀) of the SARS-CoV-2 is estimated to range from 1.4 to 3.9 (van Doremalen et al., 2020; Wu et al., 2020a). The infectivity is greater than that of seasonal influenza (0.9–2.1) and MERS (0.29–1.44), which is close to SARS (∼3) (Coburn et al., 2009; World Health Organization, 2003; Yin and Wunderink, 2018). However, global spread of SARS-CoV-2 is far greater than MERS and SARS, which might be associated with cases with mild symptom or asymptomatic cases. According to Wrapp et al. the binding of SARS-CoV-2 to the obligate receptor of Angiotensin Converting Enzyme 2 (ACE2) is of higher affinity than that of SARS-CoV (Wrapp et al., 2020), indicating that those with medical comorbidities may be at higher risks. This may also indicate a higher time to infection, even in the absence of masks (Pung et al., 2020). For example, there has been case reports of infection that took only 15 s standing in front of a stall in the vegetable market together with a confirmed case without wearing masks (Jiangbei News, 2020). Making matters worse, cases in the incubation period might also have a certain degree of infectivity (Rothe et al., 2020). For example, a case visited Germany from China, participated in a business conference, but the symptoms did not appear until that case travelled back to China. Three days later, the patient was positive in COVID-19 test. Two days later, his associates displayed symptoms and were subsequently confirmed.

2.1. The attitude towards the mask in different countries

In the past two decades, countries in East Asia have experienced infectious disease epidemics or air pollution episodes, such as Severe Acute Respiratory Syndrome (SARS), avian influenza, influenza, and haze events. Hence, wearing masks has become a pervasive in society as a way to prevent exposure. This is for good reason, as the population density in Asian countries is generally higher than that in western countries, and the crowding in a confined place will increase the infection risk or exposure. Therefore, during the COVID-19 pandemic, the public is encouraged to wear masks in public places and people often comply as a form of health-seeking behavior (Greenhalgh et al., 2020).

However, in many western advanced economies, those wearing masks are often met with suspicion in public, even causing panic in certain situation. Universal mask use in the community has been discouraged by some health authorities with the argument that masks provide no effective protection against coronavirus infection (Feng et al., 2020). Although the 1918 Pandemic (H1N1 virus) caused an estimated 40–50 million deaths worldwide, many still may view personal protective equipment (PPE) and physical barrier including wearing the mask as contrary to freedom and individualism (World Health Organization, 2005). Furthermore, there are some cultural underpinning of the use of masks as well, as it was partially prohibited by the introduction of no mask act under the background of increasing political demonstration and terrorist attacks. Since the transmission route of SARS-CoV-2 has not been fully understood, thus wearing masks should indeed be a cautionary prevention course of action.

So far, regulatory agencies and health care providers in all parts of the world have agreed on the mask use in hospital and laboratory settings, the present controversy over wearing masks is mostly focused on the effectiveness of the mask and the necessity of wearing masks in the community setting. The difference in conclusions of mask effectiveness studies is mainly due to different study contents, study designs, evaluation methods and endpoints. Understandably, good evidence on this topic is difficult to assess. Many studies used self-reported questionnaire to quantify mask uptake status, which may introduce subjective bias because the description depends on perception of participants (Barasheed et al., 2016). In addition, when the proportion of people who wear masks is too low in a group, the impact of wearing masks on disease transmission would be limited (Elachola et al., 2014).

2.2. The effectiveness of the mask

As a basic non-pharmaceutical intervention (NPI) measure, wearing a mask is an effective means of preventing respiratory infectious diseases, which could reduce the risk of infection (World Health Organization Writing Group, 2006). In this study, mask is defined as a device covering the mouth and nose providing a barrier to minimize the direct transmission of infective agents according to relevant standards, including disposable medical mask, surgical mask, and respirator with or without valve, etc. (British Standards Institution, 2019; Standardization administration of China, 2016). In a large systematic review of physical interventions to control spread of infectious diseases, Jefferson et al. concluded from 67 studies that wearing masks is effective as one of the important barriers to transmission of respiratory viruses, and evidences indicate N95 respirators were non-inferior to surgical masks (Jefferson et al., 2011). Other studies also found evidence that wearing masks can significantly reduce the risk of SARS and influenza-related diseases (Jefferson et al., 2009; Macintyre et al., 2009; Zhang et al., 2013). Aldila et al. constructed MERS determinant mathematical model and found that compared with auxiliary nursing and government publicity, wearing masks is the optimal choice for reducing the number of infections (Aldila et al., 2018). In addition, the costs of wearing masks is also the lowest for society, as it is a simple low-cost intervention (Aldila et al., 2018). During SARS epidemic, a survey conducted in the United States, Singapore, Chinese Taiwan, and Hong Kong showed that the meaning of wearing masks has exceeded their direct effects in disease prevention and has become a means of raising public awareness of other NPIs, such as isolation (Pillemer et al., 2015). Barasheed et al. systematically analyzed the utilization and effectiveness of masks by integrating 12,710 samples from more than 50 countries in the world, and found that wearing masks in crowded places could reduce the risk of respiratory infections by 20% (Barasheed et al., 2016). A study in Hong Kong found that the odds ratio (OR) value of wearing masks in public places was only 0.36, which was lower than that of living room disinfection (OR = 0.41) and frequent hand washing (OR = 0.58), indicating that wearing masks effectively restricted the community spread of SARS-CoV in Hong Kong (Lau et al., 2004).

3.1. To establish mask use strategies for different population and scenarios

As Tedros Adhanom Ghebreyesus, the WHO Director-General, mentioned on March 18, 2020, “do not assume you will not be infected, prepare as if you will die” (Ghebreyesus, 2020). The Government of China has implemented a risk-based mask use strategy for general public, people in public congregated places and confined congregated places, confirmed/suspected cases and close contacts, and occupational exposed workers under various scenarios, which could be used as a reference (Table 1 ). As an example, during the COVID-19 pandemic, it is suggested to wear the mask in congregated places such as offices, shopping malls, restaurants, conference room, etc. or relatively confined environments such as elevators, transportation vehicles, etc. The mask is generally used by general public, while the respirator or a filtering face piece, which is designed to protect the wearer from exposure to airborne contaminants, is mainly used by health care workers especially during AGP (European Centre for Disease Prevention and Control, 2020). The exhalation valve is sometime used in the respirator in order to reduce the breathing resistance. However, the inhalation valve closes and the exhalation valve opens of the mask when the wearer breathing, implying that the exhaled gas is not filtered and directly discharged into the surrounding environment. As a result, the respirator recommended for suspected cases, confirmed cases, asymptomatic carriers, and close contacts must not contain the valve (CDC, 2020c). Moreover, considering the probable insufficient mask production, masks could be repeatedly used under the prerequisite of public health protection in areas with middle to low risks.

3.2. To scientifically publicize the use of masks

Rational guidance should be provided concerning the use of masks. The content of messages to the public should include 1) the necessity of wearing the mask; 2) selection of the proper masks; 3) rational use of the mask in different situations; 4) disposable of the mask; and 5) other prevention and control measures which should not be neglected. There is not a single measure that could provide complete protection to the public. Therefore, mask use must be combined with hand hygiene, ventilation improvement, reduction of gatherings, and social and physical distancing. To inform the public, the government could 1) invite mainstream press such as TV stations, broadcasts, newspapers, etc. to participate in mask education; 2) spread relevant knowledge via social media (e.g. Twitter, Facebook, and Instagram) or display screens and billboards in public places; 3) hand out mask instruction materials to the public; and 4) carry out training and seminars in places such as hospitals, schools, kindergartens.

3.3. To guarantee sufficient supply of masks

As the use of masks during the COVID-19 pandemic would contribute to the rapid consumption of masks in limited time, two essential countermeasures should be taken into consideration. The government should timely stimulate mask production. Many countries have been facing a severe shortage of medical resources, including medical masks. In this circumstance, the mask price increased sharply, and the public stole or fought for masks in some regions; in addition, diplomatic disputes even arose. To solve this problem, the government could 1) procure surgical masks globally through different channels and means; 2) distribute masks in accordance with risk level; and 3) explore prospects of local production. Research on mask reuse should also be encouraged. For example, Song et al. has proposed an approach for medical mask use using hairdryer, and they are still working on further improvement (Song et al., 2020). After the treatment, the medical mask could be used by the public, but the reuse in a hospital settings is still unexplored.

The authors would like to acknowledge all health-care workers involved in the diagnosis and treatment of patients during the pandemic in the globe. The present perspective has not been subjected to the peer and policy review from China CDC, and therefore does not necessarily reflect the views of the China CDC and no official endorsement should be inferred.