Lockdown in Sydney doesn’t mean staying locked in. It’s Covid-safer to be outside
Since the Sydney lockdown was implemented there have been news articles and social media posts complaining about how many people are outside. But this is likely the safest place for them to be.
Let’s go through the science.
It was first thought that the majority of Covid spread was through droplets, either falling on to the ground or items, or by touch, such as touching a door handle.
There was a debate for some time but now the airborne spread of Covid, through aerosols in the air as well as droplets, has been acknowledged by the World Health Organization, leading medical journals (eg the Lancet), globally and in Australia.
Aerosol transmission of Covid is argued to be the dominant form of transmission. Someone does not have to be coughing or sneezing to transmit Covid if they are infected; and they can transmit before they even have symptoms themselves.
A characteristic of the pandemic is the super-spreader events – where one infected individual expels the virus into a crowded, indoor setting with poor ventilation, which leads to many secondary cases. The Avalon RSL and the West Hoxton birthday party are examples of this in New South Wales.
A major way to reduce the transmission of Covid is to avoid breathing in the virus – by being in places with excellent ventilation (fresh air), filtering the air, reducing time indoors and reducing crowding. Of course, we also have other important defences, including vaccination, testing and isolating when symptomatic, isolating when a contact has Covid, wearing a mask and hand washing.
Footage of packed British beaches in the summer of 2020 and parks in downtown Toronto prompted outrage, but no clusters emerged.
Outdoor transmission of Covid does occur but is much less likely than indoor transmission. Data from the UK in late 2020 showed that in the small number of cases where transmission occurred outdoors, people were in close proximity to one another for a long time or the gathering was mostly outdoors but included some indoor mixing.
Data from Ireland found that just 0.1% of transmission occurred outdoors. A February systematic review on transmission of Covid outdoors concurred with these findings and found that not wearing a mask was also a risk factor for Covid transmission outdoors. The systematic review reported about a 20 times increased risk of Covid transmission indoors compared with outdoors.
NSW Health has confirmed that there have been no known outdoor transmissions of Covid since the start of the pandemic. This includes the more transmissible Delta variant. This is particularly notable given sustained high-testing levels and the low vaccination rate in NSW.
Getting outdoors for physical activity is one of the most important things we can do for our health generally and is even more important during Covid times. Remaining in one’s own household “bubble” while outdoors is the safest approach but, when allowable, meeting family and/or friends outdoors can be the safer way to socialise and ultimately support our mental health and wellbeing.
There are always nuances to information and so here are some specific examples.
Attending a gym class outdoors where the instructor and 50 attendees are shouting while huffing and puffing due to physical exertion is not likely the safest way to enjoy the outdoors when community transmission of Covid is high and vaccination rates are low.
Swimming in an outdoor pool but then mingling in a crowded indoor change room for a long period afterwards is not the most ideal way to enjoy an outdoor Covid-safe(r) activity. Walking around the block with family is a much safer way to enjoy the outdoors.
With the importance of fresh air in mind, we can weigh all the factors relevant to transmission: masks are less important outdoors but still helpful in crowded or high-risk outdoor environments (think Covid testing).
Social distancing is always useful, indoors and outside, but particularly important indoors where there is little
fresh air. Hand washing is still useful, and vaccines decrease risk of transmission.
Much of Covid transmission is due to airborne spread.
As we know, reopening needs to be a staged approach and until we have excellent vaccine coverage of the entire population (and hopefully few new variants of concern evading vaccines), we will continue to need to follow Covidsafe practices.
Being outdoors is a great example of a Covid-safe(r) practice. Bars, restaurants, cafes, entertainment venues, long-term care, day care and schools should focus on using their outdoor environments as much as possible. Concerts and cinemas should be held outdoors instead of indoors. Gyms and exercise classes should operate outdoors if possible. If being indoors is required, it’s best to open all windows and doors and leave them open, to wear masks, distance and get vaccinated, if you can.
• Alexandra Martiniuk is a professor of epidemiology at the University of Sydney
• Joseph Freeman is studying a PhD in epidemiology and public health at University of Sydney