WHAT'S NEW - COVID-19 Public Transport - The Risks

COVID-19 Public Transport - The Risks

Despite early fears of high transmission, the risk from public transport appears low and can be managed, especially in groups without other risk-elevating factors. 

In fact transmission associated with public transport is very hard to find, especially in areas where adherence to universal mask use is high.

What's Happening Now?

Before lockdown was announced in the UK public transport use was already falling, fuelled by fears of viral transmission. By the time of the announcement bus travel across the UK had already fallen by nearly 70%. After the announcement tube use in London dropped by 95%. Now that restrictions are easing and people are returning to work the statistics seem to show a reluctance to return to public transport. 

The table below compares passenger numbers since lockdown with equivalent historic dates (1)


There is some comfort to be taken in increased journeys by cycle but this is counterbalanced by mass transit reducing the air pollution that makes people more susceptible to COVID-19 too. Interestingly bus travel is increasing faster than the tube here and in the USA – it seems that people feel ‘safer’ overground than underground and want to limit time spent in contained areas such as trains and stations.

What’s the risk?

As ever, this is a difficult question to give clear-cut answers to and we need to poke at it from a few different angles. Our first problem is that early in the pandemic an economics professor at MIT published a paper (2) claiming New York City’s subway system was:

"…a major disseminator – if not the principal transmission vehicle – of coronavirus infection during the initial take off of the massive epidemic that became evident throughout the city during March 2020."

Many articles cited this report in the opening weeks of the pandemic, leading to politically-motivated calls to shut down New York’s transit system in its entirety. In addition public health experts were urging people to avoid crowds, enclosed spaces, and close contact with others—precisely the environment one finds in any mass transit system. 

The challenge is that MIT paper didn’t trace a single COVID-19 case to a subway journey with an infected passenger. 

Essentially the paper mapped subway turnstile data against infection rate by zip code, and claimed that the flattening of New York City’s epidemic curve was linked to a 65% decline in ridership that occurred in the first half of March. This is a classic case of trying to fit the data around your position – or the Texas Sharpshooter Fallacy. Fire a bullet at a barn door, draw a target around it and shout ‘bullseye’.

In fact the MIT paper provided no statistical evidence, ignored significant confounding factors and was easily debunked; for example the report showed that Manhattan’s dense, subway-rich neighbourhoods had lower infection rates than car-dominated Staten Island. Since its publication – and widespread dissemination - combined with legitimate concerns about close contact with others there has been an assumption of danger about public transport that thus far data has not borne out. 

In fact evidence is still lacking that public-transit systems have played a role in COVID-19 transmission at all and a growing body of evidence is pointing in the other direction. 

Clusters

A ‘cluster’ is defined as more than three cases that can be traced to a common event or venue, excluding transmission within households. 

The challenge is that some countries have been better at contact tracing than others - the evidence is less robust in the UK and US which lag behind other developed countries in both contact tracing and coronavirus testing. 

But there are other countries with better data we can look at: it’s the same virus and mass transit systems are broadly similar in nature so comparisons are valid – we just need to try to identify and control for any confounding factors. 

  • In Paris, a study (3) in June found that none of the city’s 150 coronavirus clusters from early May to early June originated on the city’s transit systems.As of July 15th four transport clusters had been identified in Paris, accounting for roughly 1% of 386 total clusters, according to data from Santé Publique France.
  • A similar study (4) in Austria found that none of the 355 case clusters in April and May were traceable to public transport.
  • Milan was particularly hard-hit but since reopening public transit systems there have been no subsequent spikes in infection rates. 
  • Japan - with some of the world’s busiest rail networks - had very few infections at all and no reported spikes in Tokyo since Japan began reopening its economy. 
  • In South Korea, officials traced a post-peak outbreak in Seoul not to public transit but to a lack of social distancing at the city’s reopened nightclubs. 

While it is true that - by and large - mass transit systems are carrying fewer passengers at a lower density than before the pandemic, the evidence does indicate a far less sinister role for transit than the MIT report suggested. And were public transport a global super-spreader, then Hong Kong with 7.5 million people dependent on a public transport system that before the pandemic was undertaking 12.9 million passenger journeys a day should have seen a huge outbreak. It didn’t. 

Also passenger volumes in Hong Kong fell considerably less than in other mass transit systems around the world - yet Hong Kong has recorded under 5,000 COVID-19 cases. 

Reducing Risk

There is nothing in life that is entirely risk-free. It’s difficult to put precise numbers on the risk attached to any activity in the absence of robust data, but it seems that provided sensible precautions are taken the risk of using public transport is very low for the vast majority of the population. In areas where adherence to universal mask use is high the clusters associated with public transport are very hard to find. In the UK the acceptance of the need for masks on public transport is good and will have a huge impact, as will physical distancing. As ever, respiratory droplets are the major driver of spread. Surfaces are less likely to be involved in transmission but handrails and lift buttons etc will have been touched by a lot of people before you. These are genuine ‘high-touch’ surfaces and so carry a higher risk – so be aware of and manage that risk. If we take a slightly broader view of risk, using public transport (especially rail) rather than a car plays a crucial role in combating climate change and air pollution - and air pollution leads to significantly higher COVID-19 death rates (5). Additionally if increased car use leads to increased particulate emissions it will exacerbate a lot of the health disparities found in poorer communities. 

Top Tips

So, early speculation has not been borne out by the data, the risk from public transport appears low and can be managed, especially in groups without other risk-elevating factors. 

  • Wear a mask;
  • Take hand sanitiser with you and use it lots;
  • Don’t touch your face; • Try to avoid busier times (TFL has an app to help with this in London);
  • Cycle if possible - an extra 1,700 Santander cycles and 14 additional docking stations have been added across London.


References

1. Department for Transport. Transport use during the coronavirus (COVID-19) pandemic. Official Statistics. s.l. : Office for National Statistics, 2020.

2. Harris, Jeffrey E. The Subways Seeded the Massive Coronavirus Epidemic in New York City. Social Science Research Network. 13 April 2020.

3. France, Santé Publique. COVID-19 : point épidémiologique du 4 juin 2020. santepubliquefrance.fr. [Online] 4 June 2020. [Cited: 21 August 2020.] Click here

4. Austrian Agency for Health and Food Safety. Epidemiologische Abklärung am Beispiel COVID-19. AGES. [Online] 19 August 2020. Click here

5. Wu, Xiao, et al. Exposure to air pollution and COVID-19 mortality in the United States: A nationwide cross-sectional study. Harvard University. s.l. : medRxiv, 2020.