(C) Richard Jones

SARS-CoV-2 (coronavirus) is a virus - it travels and can aggregate in the air.

COVID-19 is the disease that the virus can cause.

Rarely do people become infected outdoors in the fresh air.

Plentiful fresh air is more important than only washing hands.

Why 'Fresh Air'?

Coronavirus is transported in droplets and aerosols;

By keeping at least 2m from an infectious person, it is possible to avoid droplets and the majority of aerosols;

Under certain conditions, aerosols can aggregate in the air, negating the effect of social distancing;

Plentiful fresh air will reduce the possibility of aerosols aggregating, be that outdoors or indoors with ventilation.


Infectious People

By wearing a mask with a good seal against the face, many droplets and aerosols will be restricted from spreading in the air, but not all.

People are at their most infectious before developing symptoms.

With as much as 40% of infectious people asymptomatic (without symptoms), a mask can be most useful before the onset of symptoms.

Healthy People

If a healthy person gets infected, wearing a mask with a good seal against the face can reduce the viral dose. A person without a mask may receive a higher dose.

There is a relationship between viral dose and severity of symptoms. The larger the dose, the more likely the symptoms will be worse.


A visor can block some droplets, but does not restrict the spread of infectious aerosols.


The use of our voices can affect the spread of coronavirus.

By raising our voices, more aerosols are generated.

COVID-19 – Safer Communities

Dr Huw Waters, Dr Eilir Hughes


As people slowly return to their old routines, the risk of catching SARS-CoV-2 and potentially becoming sick with COVID-19 remains very real. Opening shared buildings, such as schools and offices, will increase the risk of transmission between people, as the virus is present in the community. To date, transmission risk management has included maintaining social distance from others and frequent hand washing.1 An increasing body of evidence shows that the risk of catching SARS-CoV-2, hence developing COVID-19 symptoms, could be reduced further by better understanding virus transmission and how it can be managed.

SARS-CoV-2 and the population

SARS-CoV-2 can infect people of all ages, with COVID-19 affecting people more with increasing age. SARS-CoV-2 and its effects on younger people continues to stir debate, although it does not appear as problematic as for adults.

Children account for 1-7% of all known infections, despite accounting for up to 21-25% of the population. They have a milder disease course with deaths extremely rare.2–6 As with any testing process, the real number is likely to be higher. This could be down to unknowingly being infected with SARS-CoV-2 and not seeking a test due to mild or no symptoms, or difficulties processing tests accurately (e.g. testing negative using the standard procedure, despite the presence of SARS-CoV-2).7,8

Children appear to develop milder COVID-19, with little or no symptoms (asymptomatic) for reasons that are still being investigated, but protective measures should not be ignored.3,9 Although rare, children have become seriously ill from SARS-CoV-2.10,11 An investigation of the very few children admitted to intensive care for Paediatric Multisystem Inflammatory Syndrome (PIMS) demonstrated high immediate survival, but the long-term effects are unknown.12

Since a small proportion of cases are attributed to children, and of those infected having milder COVID-19 symptoms, the inference is that they are less likely to contract SARS-CoV-2 than adults. A summer camp had to close due to an outbreak of SARS-CoV-2, sending home all 597 staff and attendees. At least 58% of the 344 attendees had been tested, with 76% having a positive result.13 Attendees had an age range of 6-19, median 12, and adds to growing evidence that children of all ages are susceptible to contracting SARS-CoV-2.10,13,14 Where follow-up information was available, 26% were asymptomatic, with the remaining 74% reporting subjective or documented fever, headache and/or sore throat. Quantifying the risk for children is still not possible due to the need to conduct further research, however, there is a risk of contraction.

An absence of COVID-19 symptoms does not mean a reduction in infectiousness. Children may be just as infectious, or more infectious than adults.15–18 Therefore, the greatest risk of becoming sick with COVID-19 is to adults that come in to contact with infectious children, and not to the children directly.

In contrast, those most affected by SARS-CoV-2 either have underlying health conditions (e.g. immunocompromised, diabetes, heart disease, obesity) or are elderly. COVID-19 symptom severity increases with age. Figure 1 shows the age-specific mortality rate per 100,000 versus age, for England and Wales who have caught SARS-CoV-2.19 Although most adults will not become seriously ill from SARS-CoV-2, there are still many unknowns regarding long-term health effects, which will only become apparent with time.20–24

Figure 1 - Age-specific mortality rate per 100,000 increases with age. Very few death have been registered in those below 55 years of age.19

Reducing risks

How SARS-CoV-2 spreads

SARS-CoV-2 is a respiratory virus that is spread in droplets and aerosols.25–27 These are exhaled from infected individuals during breathing, speaking, coughing and sneezing.25 The World Health Organisation, as well as Public Health Wales and Public Health England, maintain that SARS-CoV-2 is primarily spread through close contact and droplets – not by aerosol transmission.28–31 This position is being challenged, with growing evidence showing that SARS-CoV-2 is spread via aerosols suspended in the air.32–35

Heavier droplets contribute to transmission by being projected on healthy people, who are within 2m of an infected individual. Furthermore, droplets containing SARS-CoV-2 also settle and contaminate surfaces within this distance, which others may then touch and subsequently become infected. Droplets settle on the ground within seconds.25

Aerosols, just like droplets, are at their highest concentration within 2m of an infected person but can travel tens of meters.36 These aerosols can accumulate and remain infectious in indoor air for hours and can be easily inhaled deep into the lungs.34,37

There are two respiratory virus transmission pathways: contact (direct or indirect between people and contaminated surfaces) and airborne. Much has been made of tackling contact transmission through advice on maintaining social distance as much as possible and regular hand and surface washing.28,29,31 However, little focus has been given to airborne transmission. Figure 2 shows how the virus can transmit from an infected individual. The method of infection depends upon the droplet size; small droplets are known as aerosols.37,43

Figure 2 - A diagram showing the difference in motion of larger and small droplets. In this context, small droplets are known as aerosols and can remain suspended in the air in a room for hours.37

Research into SARS-CoV-2 has drawn attention to the real transmission of respiratory diseases in general.27,33 One study concluded that 57% of a group of healthcare professionals had caught SARS-CoV-2 via aerosols.38 Another indicated that under certain conditions, aerosols account for over 90% of a vulnerable person’s exposure from an infected individual.36

Aerosol generation

In terms of respiratory diseases, the emphasis has traditionally been placed on coughing and sneezing, which yield visible droplets and large quantities of aerosols.39 Aerosols, which may contain SARS-CoV-2 are released during breathing, speaking, singing, coughing, and sneezing.25,40 A positive correlation has been demonstrated between the loudness of speech and the number of aerosols released from a person.39 Further, some individuals release significantly more aerosols for a given activity, leading to the suspicion that respiratory diseases are primarily driven by super-spreaders - a large number of cases driven by a handful of people.41

A handful of super-spreading events have come to light during the pandemic, with a focus on the activity. Following a 2.5-hour choir practice of 61 attendees, with one of those being infectious, 32 were tested positive for SARS-CoV-2 with a further 20 probable cases.40,42 Not all of those present are believed to have come within 2m of the infected person.40 There have been other examples of significant outbreaks of SARS-CoV-2 infection across the world, including a religious service where up to 2,500 were infected.43–45 Outbreaks affecting hundreds of workers have also been observed at abattoirs and other food-processing plants.46,47 It is believed that not only cold and damp conditions play a part, but that workers are talking loudly and shouting in noisy environments. In Wales, there have been outbreaks in Llangefni, Wrexham and Merthyr Tudful.

Lessons from history

During the Spanish Flu pandemic of 1918-19, as many as 50-100 million persons died worldwide, with many others falling ill. The accepted view is that little could have been done to prevent spreading or to treat those infected. This view has been challenged using observations that individuals infected with tuberculosis or flu had reduced mortality rates and increased rates of recovery when placed in outdoor convalescence.48

By the time of the 1918 flu pandemic, placing tuberculosis patients in the open-air had become common.49 In 1908, there were at least 90 sanatoria in the UK – hospitals built specifically for tuberculosis victims.50 In these sanatoria, patients were moved and kept outside for as long as possible, while kept warm with hot-water bottles and blankets. Open-air hospitals had already shown benefits for tuberculosis patients.

During the 1918 flu pandemic, one hospital demonstrated significantly better outcomes in terms of reduced mortality and increase rates of recovery for flu. Patients were given “a maximum of sunshine and of fresh air day and night”.48 The motivation for this hospital came from the observation that sailors from the most poorly ventilated areas of the ships in East Boston also had the worst cases of pneumonia. Furthermore, sailors, such as those on board the ships at East Boston, were particularly vulnerable to influenza infection, because the influenza virus is readily transmitted in confined quarters.48

Increasing time outdoors also increases exposure to UV-light, which has been shown to inactivate viruses51,52, improve mental health and concentration, and boost vitamin D – essential for a healthy immune system.48,53

Figure 3 shows a New York school classroom in 1911 where the windows have been left wide-open. The principles of sanatoria were extended to schools. Fresh air was deemed essential.54 The use of open-air schools for tuberculosis treatment came to an end with the use of antibiotics.49 It should be noted that antibiotics are only effective against bacteria such as tuberculosis, but not viruses such SARS-CoV-2.

Figure 3 - Children in a New York school classroom in 1911, where large windows are wide-open for maximum ventilation. These were built for the prevention of tuberculosis spread.54

In a study of 318 outbreaks, where three or more people were infected with SARS-CoV-2, all occurred in indoor settings.55 One study concluded that the odds of SARS-CoV-2 transmission from an infected person is ~20 times higher in a closed environment.56 This has been demonstrated widely with a correlation between a reduction of cases and the prohibition of large gatherings indoors.

Intuitively, outdoors there is plenty of fresh air to dilute and blow away aerosols that contain SARS-CoV-2, significantly reducing the likelihood of it encountering others. Additionally, sunlight has been shown to inactivate 90% of SARS-CoV-2 virus particles within 19 minutes.52 As many activities as possible should be conducted outside for this reason.

If activities need to be conducted indoors, then increased ventilation can dilute the indoor air thus reducing the risk of SARS-CoV-2 exposure to others. A tuberculosis outbreak at a university in Taiwan came to an end when increased ventilation led to a 97% reduction in the spread.57 Increased ventilation, through opening windows and doors, can reduce the risk of SARS-CoV-2 spread if an infected person is present. Ventilation can also be increased by using existing air systems to pump in air from outside.58 Caution should be taken not to recirculate indoor air and for people to avoid being in an airstream from an infected person.25 That is, avoiding paths of flowing air that could contain aerosols of SARS-CoV-2. It should be noted that the more people present in a room, the more ventilation is needed to ensure regular air changeover. Figure 4 shows how increased ventilation can be achieved either by bringing in fresh air or pushing stale air out.59

Figure 4 - Ventilation can be increased by either bringing fresh air in or pushing stale air out. Fans can increase the speed of air changeover.59

It may be difficult to determine if there is enough air changeover. One study on using ventilation to remove the original 2003 SARS virus and flu suggested 9 air changes per hour.60 This can be measured using the level of CO2 present as a proxy. Outdoors, the level of CO2 is 400ppm. In a well-ventilated indoor environment, the level is approximately 800ppm. Good ventilation can be indicated by aiming to achieve a figure no more than 800ppm.42,61-63 This can be automatically achieved using a capable air circulation system, or a combination of an inexpensive CO2 sensor and open windows and doors.

In addition to ventilation efforts, advanced air filtration systems can also help. The best results were deemed to be provided by a mixture of ventilation and air filtration.27,61,62 In a study investigating the indoor spread of airborne tuberculosis, a combination of air filtration (HEPA filter) and ventilation was found to reduce the average droplet and aerosol concentrations, and therefore the risk of infection, by between 30-90%.64 The same finding may also be relevant for SARS-CoV-2. Small portable advanced air filter systems (HEPA) can be purchased for the price of a tablet computer (e.g. iPad).


At the beginning of the pandemic, advice around the efficacy and recommendation of masks was mixed. Healthcare workers directly treating SARS-CoV-2 had the greatest need for a mask with a concern around PPE supplies.65 Masks have been shown to work, not only in healthcare settings but for general use in terms of curbing SARS-CoV-2 spread.66,67 Mask wearing was found to decrease the increase in transmission rate by as much as 40%.68 Masks filter out a lot of viral particles but not all.69

Detecting and stopping SARS-CoV-2 transmission is more challenging compared with other respiratory viruses, in that studies suggest that individuals are most infectious before the onset of symptoms.70 Figure 5 shows that the peak infectiousness of those with SARS-CoV-2 is before the onset of symptoms. For other respiratory viruses, individuals tend to be most infectious after symptoms have become apparent. For this reason, wide-spread mask-wearing is important to reduce virus transmission from persons who are, unbeknownst to them, pre-symptomatic or asymptomatic.66 Although some masks perform better than others, when a good fit is ensured, basic cloth coverings have been shown to work reasonably well.25,69

Figure 5 - A chart showing the relative SARS-CoV-2 transmission probability with time. An individual is most infectious before the onset of symptoms.70

Viral load

Masks are most effective in reducing the amount and spread of infectious aerosols from an infected person. However, masks may also provide some protection for healthy persons as well. Masks, depending on the type, filter out most viral particles, but not all.25,69

Asymptomatic infections do not stop the transmission of SARS-CoV-2 to others and remain a clear threat to those with underlying health conditions and the elderly. There may be, however, a benefit to asymptomatic infections if they lead to higher rates of exposure.25,69 Exposing society to SARS-CoV-2 without the unacceptable consequences of severe illness, using wide-spread masking, could lead to greater community-level immunity and slower spread as we await a vaccine.69,71 Other research has also observed a correlation between viral load and the severity of symptoms.72 An increase in the number of asymptomatic infections has been attributed to increased mask-wearing.69

Figure 6 shows how a mask on an infected person can help reduce the number and spread of virus particles. Healthy people can also see a benefit of mask-wearing by reducing the possible received viral load.25,69

Figure 6 - The effect of masks on both infected and healthy persons. A mask can act as a source-control for an infected person but may also protect healthy individuals by reducing the viral load consumed.25

Care settings

Nursing homes provide care for the most vulnerable in society, including the elderly and those with underlying health conditions – those at most risk from SARS-CoV-2. Although not all explicitly attributable to SARS-CoV-2, in May 2020 the Office of National Statistics reported 20,000 excess deaths in care homes in England and in Wales as a consequence of the pandemic.73

According to the US Government’s Centre for Disease Control, nursing homes have been documented as having high transmission rates for infectious diseases for a range of reasons including crowding, sharing of bathroom facilities and gathering in common areas as well as low preparedness for infection control.74 Challenges facing nursing homes include staffing shortages and frequent staff turnover, high resident-to-staff ratios, supply shortages, and inadequate infection prevention and control measures.

The inherent risk of nursing home environments could be reduced by examining some of the previous points, in terms of increasing time outdoor and increase ventilation and the use of air filtration systems. For shared facilities in high-risk environments, such as toilets, the application of negative pressure is advised. This could be in the form of strong extraction fans.

Winter pressures in primary care

Control measures for reducing the spread of SARS-CoV-2 have wider benefits. The number of flu cases detected in Australia for 2020 has plummeted compared with 2019 figures, despite increased testing. This has been attributed to measures discouraging close social contact, hand washing, and increased willingness to stay at home if feeling unwell.75

Patrick Vallance, the UK’s Chief Scientific Advisor (GCSA), commissioned the Academy of Medical Sciences to evaluate the risk and devise potential solutions for seasonal influenza circulating at the same time at SARS-CoV-2. The most recent significant influenza season in Winter 2017/18 led to over 17,000 excess respiratory deaths, and NHS Trusts cancelling all elective surgery in January 2018.76 On July 24th, the Welsh Government announced the “largest ever flu vaccine programme”, enabled by UK Prime Minister, Boris Johnson, announcing an additional £3 billion for the NHS across the UK.77,78

The prospect of flu circulating within our communities is concerning. However, continued emphasis on the control measures used for SARS-CoV-2 can help with reducing transmission, and the burden it could place on our already-stretched health services. This is even more so considering the backlog of cancelled routine NHS services since March. Dr Andrew Goodall, the Chief Executive of NHS Wales, suggested that it may take as long as four years to clear the backlog created from cancelled appointments due to SARS-CoV-2.79


Although much has been made of airborne SARS-CoV-2, potential spread via droplets should not be ignored. Efforts should be directed towards seeking opportunities to be outdoors and increasing ventilation for indoor settings. The use of appropriate air filtration systems should also be considered. This is in addition to maintaining social distancing and adequate hand washing.

Although children do not appear to be severely impacted by SARS-CoV-2, there is no information to doubt that they remain a risk to adults. It would be prudent for children and adults to wear face-coverings or masks with a good seal against the face, to reduce the amount of potential SARS-CoV-2 particles being dispersed from an infected individual. The US Government’s Center for Disease Control (CDC) recommends that anyone above the age of two should wear a mask.

Jose-Luis Jimenez, a professor of Chemistry and an aerosol expert shared these recommendations:

  • Don’t go to indoor public spaces unless it’s absolutely necessary;
  • If you are indoors, spend the least of time there as you can;
  • Make sure when you’re indoors, the room is well-ventilated, including mechanical ventilation like particle air filters and natural ventilation like open windows and doors;
  • Always wear a mask indoors;
  • Make sure the mask fits and doesn’t have gaps;
  • Anyone who is talking to others – especially to a large group – should be wearing a mask. Shouting and singing are especially problematic and should be avoided.


  • Avoid close-contact and ensure regular surface and hand washing;
  • Spend as much time outdoors and ensure well-ventilated indoor spaces (gauge with CO2 levels);
  • Ensure wide-spread mask-wearing.


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