Context
The RaISe research paper ‘Exit’ from COVID-19 ‘lockdown’: Health-related issues (20 May 2020) contained sections on transmission of the virus SARS-CoV-2 and two of the key issues – social/physical distancing from other people and the use of face coverings. This article updates these areas, looking at the guidance in place, the science behind it and the impact on the ‘exit from lockdown’.
This article was updated on 3 July 2020.
Introduction
The two main routes of transmission of the virus are thought to be respiratory droplets and contact. Droplets are generated when an infected person coughs or sneezes. Any person who is in close contact (within one metre) with someone who has respiratory symptoms is at risk. Droplets also land on surfaces where the virus can remain viable as a source of contact transmission.
A number of factors influence how effectively a virus spreads. The average number of viral particles needed to establish an infection in an individual is known as the infectious dose. Given how rapidly SARS-CoV-2 has spread, its infectious dose is likely to be relatively low (a few hundred to a few thousand particles). Viral load relates to the number of viral particles being carried by an infected individual and shed into their environment. If an individual has a high viral load, they are more likely to infect other people.
The aim is that the wearing of face coverings/masks and maintaining of social/physical distance reduces transmission of the virus, particularly from those who are ‘out and about’ showing no symptoms and appearing to be healthy.
It is known that the virus causes little to no noticeable illness in some people. Researchers at the University of Oxford reviewed 21 published reports and found that studies have shown:
- A wide range of asymptomatic cases (no noticeable symptoms) testing positive (5% to 80%);
- Symptom-based screening will likely miss many cases;
- Some ‘asymptomatic’ cases will go on to become ‘symptomatic’ over the next week (‘pre-symptomatics’); and
- Children and young adults can be ‘asymptomatic’.
In one of the studies from China (involving 375 cities), the asymptomatic people were estimated to be around 55% as contagious as those with more noticeable symptoms, but likely the source of almost 80% of further infections, due to there being more of them and the likelihood that they were ‘out and about’ (before ‘lockdown’). In another study from Italy, in the town of Vò, all 3000 residents were tested in March 2020 and 60% of the people who tested positive had no symptoms.
A new study from the Scripps Research Translational Institute in the US, also emphasises just how many cases of SARS-CoV-2 infection are asymptomatic. Researchers assessed studies of 16 different cohorts, including groups of cruise ship passengers, prison inmates, and nursing home residents tested for COVID-19:
What virtually all of them had in common was that a very large proportion of infected individuals had no symptoms…Among more than 3,000 prison inmates in four states who tested positive for the coronavirus, the figure was astronomical: 96% asymptomatic.
Looking at all their data, they estimate that around 40–45% of people contracting the virus are likely to be asymptomatic. They also infer that people who showed no symptoms are, nevertheless, liable to spread the virus over 14 days or more after infection.
Masks and face coverings for the general public
There is little dispute that medical masks (respirators and surgical face masks), help reduce the spread of the virus in healthcare settings. The debate has been ongoing as to whether wearing a face covering or mask protects the public against contracting, or from spreading, the virus.
WHO guidance
The WHO remains of the view that where medical masks are in short supply, they should be reserved for health workers and at-risk individuals and believes that medical masks are best used by those who are sick and showing symptoms or are caring for people suspected to have coronavirus, either in a hospital or community setting.
Taking into account the studies evaluating pre- and asymptomatic transmission, the WHO has updated its technical guidance (from 5 June 2020) to advise that governments should now encourage the public to wear masks (medical or non-medical depending on the situation) as part of a comprehensive approach. Table two of its guidance (reproduced below) lists situations and settings where mask wearing is now recommended.
| Situations/Settings | Population | Purpose of Using Mask | Type of Mask to Consider Wearing (if recommended locally) |
| Areas with suspected or known widespread transmission and limited or no capacity to implement other containment measures such as physical distancing, contact tracing, testing, isolation and care for suspected and confirmed cases. | General population in public settings, such as grocery stores, at work, social gatherings, mass gatherings, closed settings including schools, churches, mosques etc. | Potential benefit for source control. | Non-medical mask. |
| Settings with high population density where physical distancing cannot be achieved; surveillance and testing capacity, and isolation and quarantine facilities are limited. | People living in cramped conditions, and specific settings, such as refugee camps, camp-like settings and slums. | Potential benefit for source control. | Non-medical mask. |
| Settings where physical distancing cannot be achieved (close contact). | General public on transportation (e.g. on buses, planes, trains).
Specific working conditions which places the employee in close contact or potential close contact with others e.g. social workers, cashiers, servers. |
Potential benefit for source control. | Non-medical mask. |
| Settings where physical distancing cannot be achieved and increased risk of infection and/or negative outcomes. | Vulnerable populations:
*People ≥60 years *People with underlying comorbidities e.g. cardiovascular disease, diabetes mellitus, chronic lung disease, cancer, cerebrovascular disease, immunosuppression. |
Protection. | Medical mask. |
| Any setting in the community (this applies to any transmission scenario). | Persons with any symptoms suggestive of COVID-19. | Source control. | Medical mask. |
Table 1: Examples of where the general public should be encouraged to use medical and non-medical masks in areas with known or suspected community transmission (source: WHO Technical Guidance)
The WHO guidance also covers:
- Types of fabrics that can be used in a mask in the ideal combination of three layers – an inner layer of absorbent material, such as cotton; a middle layer of non-woven material, such as polypropylene; and an outer layer of non-absorbent material, such as polyester or polyester-blend;
- Mask shape; and
- Maintenance/use of masks (washing, removing, discarding etc.).
Current UK guidance
There is varying advice across the UK from the four governments about wearing masks/face coverings. However, all have been careful to state that ‘face coverings’ should be worn and not surgical masks or respirators which should be left for healthcare staff and other workers who need them.
The UK Government states that face coverings do not replace social distancing and that the evidence suggests that if you are infected, but have not yet developed symptoms, it may provide protection for others you come into close contact with.
In England, the rules are now that people must wear a face covering at all times on public transport or when attending a hospital as a visitor or outpatient. Also, a face covering must be worn in other enclosed public spaces where social distancing is not possible and where you will come into contact with people you do not normally meet. People could be refused travel or fined if they do not follow the rules.
Some passengers on public transport will be exempt, including children under 11, people with disabilities, those with breathing difficulties, and anyone travelling with someone who relies on lip reading. The rail industry will ask people to cover their face as they enter a station.
In Northern Ireland (NI), a proposal to make face coverings mandatory on public transport was expected to be signed off on 29 June, the day the measure came into force in the Republic of Ireland. However, the proposal was initially put on hold with the NI Executive stating it was seeking ‘clarity on legal advice’ on the issue. It was subsequently announced that the wearing of face coverings on most buses, trains and ferries will be mandatory in NI from 10 July. There are exemptions for those with certain medical conditions and it will not apply to children under the age of 13, or on school transport. Outdoor areas of a ferry where social distancing can be maintained will be exempt from the requirements.
The Scottish Government recommends people wear face coverings in enclosed spaces, where social distancing is more difficult and there is a risk of close contact with multiple people who are not members of your household. Examples include: entering shops or businesses, visits to a care home for the elderly, visits to adult hospitals as an outpatient and GP surgeries or pharmacies.
The Welsh Government recommends people should wear face coverings only where it is difficult or not possible to observe social distancing such as public transport or busy shops.
The scientific evidence
The evidence suggests that some infected people are contagious before showing symptoms and some never show symptoms. The key benefit from mask/face coverings seems to be that they might help prevent people who appear healthy from spreading the virus to others as they go about day-to-day life.
One category of evidence comes from laboratory studies of respiratory droplets and the ability of various masks to block them.
A recent experiment (using high-speed video) found that hundreds of droplets (from 20 to 500 micrometres) were generated when speaking a simple phrase, but that nearly all these droplets were blocked when the mouth was covered by a damp washcloth. Another study of people who had influenza or the common cold found that wearing a surgical mask significantly reduced the amount of these respiratory viruses emitted in droplets and aerosols.
Recent research in Singapore found masks serve as a mechanical barrier to the dispersion of respiratory droplets. Using laser beams and a high-speed, high-sensitivity camera to “see” the tiny droplets when a subject coughed, it could be seen that when a mask is properly worn, few or no droplets were released into the atmosphere. The scientists concluded:
- When people cough or sneeze without wearing a mask, the droplets they produce can travel 2-3m, with heavier, larger droplets dropping to the ground while smaller droplets appear to drift in the air; and
- When any type of mask is properly worn over the nose and mouth, most if not all droplets are blocked from getting out into the air or landing on someone else.
A second category of evidence comes from studies of real-world scenarios. For example, a recent study compared the COVID-19 growth rate before and after ‘mask mandates’ in 15 states and the District of Columbia. It found they led to a slowdown in daily COVID-19 growth rate. The first five days after a mandate, the daily growth rate slowed by 0.9 percentage-points and by three weeks, it had slowed by two percentage-points.
Social/physical distancing
Current distancing guidance in the UK
Across the UK, all four jurisdictions had their original ‘lockdown’ rules from late March 2020, including the closure of certain businesses, prohibiting anyone from leaving their house except for very limited reasons and for people to stay at least two metres apart from people outside their own household. All have recently set out phased plans to return life to as near normal as possible and some changes are proposed to the two-metre rule.
A variant of the rule has been in place in many countries across the world ranging from one to two metres, as the WHO guidance was for a minimum of one metre. The UK Government acknowledged that the science behind the rule was based on Public Health England’s best understanding of the risk of infection in close contact and the amount of time spent in close contact.
Following an expert review commissioned by the UK Government, from 4 July, the two-metre rule changes to ‘one-metre plus’ in England. The UK Government stated that maintaining the rule effectively made life impossible for large parts of the economy. For example, it prevents all but a fraction of the hospitality industry from operating. So, from 4 July in England where it is possible to keep two metres apart people should, but where it is not, people are advised to keep a distance of ‘one metre plus’ – remaining one metre apart, while taking mitigations to reduce risk.
For businesses, workplaces and schools these mitigations will likely include avoiding face-to-face seating; reducing the number of people in enclosed spaces; improving ventilation; using protective screens and face coverings; closing non-essential social spaces; providing hand sanitiser; and changing shift patterns.
In NI, the Stormont Executive has also agreed to reduce social distancing to ‘one-metre with restrictions’ i.e. people should keep two-metres distance where possible, but from Monday 29 June can come within no less than one metre with appropriate mitigations.
In a statement to the Scottish Parliament on 24 June, First Minister Nicola Sturgeon, kept the two-metre social distancing rule in place. She confirmed that people must comply until a “viable and safe balance” is found, stating that all of the evidence and advice she has been given recommends keeping the rule in place for the time being.
The First Minister in Wales, Mark Drakeford, has confirmed that Wales is also keeping the two-metre rule in place at present.
The science behind social distancing
The two-metre social distancing rule assumes that the dominant routes of transmission of SARS-CoV-2 are via large respiratory droplets falling on to others or on to surfaces. The recommendation can be traced back to research conducted in the 1930s, when scientists established that droplets released by coughs or sneezes will either evaporate quickly in the air or be dragged by gravity down to the ground landing within one to two metres.
However, not all scientists feel that two metres is enough, citing as an example the case of widespread transmission in a choir practice in Washington (US), raising the question of whether the virus can be spread via tiny aerosols, which can stay suspended in air for long periods.
Other research has shown that large respiratory droplets expelled with force (when coughing or sneezing), or carried by the wind, can travel further than two metres, before falling to the ground or on to a surface.
It should, however, be borne in mind that much research on airborne transmission of viruses is focused on medical settings, meaning it is less clear how even the most common viruses, never mind this new virus, might pass from person to person under everyday circumstances.
Earlier this month, a group of researchers concluded that a ‘one-size-fits-all 2-metre social distancing rule’ is not consistent with the science of exhalations and indoor air circulation. They proposed that social distancing should be adapted and used alongside other strategies to reduce transmission, such as air hygiene (including maximising ventilation to specific indoor spaces), effective hand washing, regular surface cleaning, face coverings where appropriate and prompt isolation of affected individuals. They concluded that:
- Smaller airborne droplets laden with SARS-CoV-2 may spread up to eight metres from infected individuals;
- The risk of transmission falls as distance between people increases, so relaxing the distancing rules, particularly for indoor settings, might risk an increase in infections. In some settings, two metres may be too close; and
- Viral transmission depends on multiple factors related to both the individual and the environment, including viral load (as stated earlier), duration of exposure, number of individuals, indoor versus outdoor settings, level of ventilation and whether face coverings are worn.
However, following a review of the literature, scientists from the Universities of Oxford and Dundee recently concluded that there were no indications that distancing at two metres is any safer than one metre.
Challenges
The likely low ‘infectious dose’ for SARS-CoV-2, the unknown number of asymptomatic cases and unknown ‘viral load’ that infected people are ‘shedding’, means social distancing, hand-washing, face-coverings etc. are going to continue to be important as society comes out of lockdown across NI and neighbouring jurisdictions.
Not every infected person shows symptoms, yet they may be spreading the virus and it is hoped that increased wearing of face coverings in certain settings will minimise this. In April, researchers at the University of Oxford stated that there was:
…not a single reliable study to determine the number of asymptomatics.
By 9 June, the WHO stated that the actual rates of asymptomatic transmission are not yet known. A study published in early June estimated that around 40–45% of people contracting the virus are likely to be asymptomatic, suggesting that the virus might have greater potential than previously thought to spread silently through the population.
However, what is clear is that not all activities or environments have the same risk of transmission and understanding the transmission dynamics of the virus within different settings is crucial going forward out of ‘lockdown’.