Why reduced physical distancing in public transport needs further study


By Dr. Edsel Maurice T. Salvana, MD, DTM&H, FPCP, FIDSA

Six months after the initial lockdown of the National Capital Region, people are slowly trying to get back to a semblance of normalcy. One of the less welcome signs of this process is the increasing amount of traffic on the road. 

KEEP DISTANCE Observing physical distance by one meter reduces the risk of contracting Covid-19 by 80 percent

As more businesses open, the demand for transport increases as employees physically go back to work. This presents a real problem due to the double whammy of the reduced number of public utility vehicles on the road, plus the reduced capacity from the mandatory physical distancing rules in each vehicle.

To address this problem, the Department of Transportation proposed decreasing the distance between people in public utility vehicles to less than one meter. This proposal was vetted by its own public health experts, which included at least two former health secretaries. It was met, however, with a firestorm of protest from medical groups and even within the IATF. What is the available evidence for reducing the distance between people in public transport? Are the proposed additional health measures sufficient to mitigate the risk of decreasing physical distance? How can we address these questions while minimizing the risk to the riding public?

There are three interventions with solid scientific evidence that have been found to decrease Covid-19 transmission. These are mask wearing, use of eye protection, and observing a physical distance of at least one meter. The use of medical or cloth masks can reduce the risk of Covid-19 transmission by up to 85 percent. Eye protection, such as face shields, can decrease the risk by 78 percent. Physical distancing of at least one meter can decrease the risk by 80 percent. 

Combined, all three measures can theoretically decrease the risk of transmission by more than 90 percent. This is, however, an estimate and can be affected by how well everyone adheres to these measures. 

If we make a cursory inspection of most places in Metro Manila, we typically see some people wearing their masks under their chins, their face shields on top of their heads, or not wearing a mask or face shield at all. Therefore, physical distancing measures may act as a fail-safe when personal protective equipment such as masks and face shields are not properly worn.

In addition, recent data has shown that in the presence of poor ventilation, distance alone may not be a good enough deterrent to Covid-19 spread. A study of an outbreak on a 100-minute bus ride in China with one infected passenger showed that 34 percent of people in the bus developed Covid-19. A significant number of patients who got infected were several seats away from the index case. This was early in the epidemic and so none of the people in the bus wore masks, and the air-conditioning was recirculating air. It is unclear what would have happened if the passengers had worn masks and face shields.

Since the number of new cases in NCR remains relatively high, backing off on mitigation measures and packing more people in public transport may significantly increase the number of new daily cases. A modelling study by HPAAC projected about 686 cases a day after reduction of physical distancing from one meter to 0.75 meters. It is unclear if these cases can be decreased by strict adherence to the “seven commandments” advocated by former Health secretary Dr. Manuel Dayrit’s group.

When there is a disagreement among experts, the best way forward is to collect more data. Decreasing physical distance can increase risk. We do not know if this can be neutralized by additional measures. There are no studies, local or international, that have specifically looked at combining mask and face shield without doing proper physical distancing. Doctors do wear personal protective equipment in order to approach and interact with patients at less than one meter, and this is clearly effective. Unfortunately, the level of protection and adherence to strict measures in medical settings is different from what occurs in a jeep or bus. Aside from uncertainty regarding the degree that cloth masks and makeshift face shields decrease transmission, the issue of adherence is a potential Achilles heel to this approach.

Too much is at stake to proceed with a plan that is not properly supported by strong scientific proof. A widespread rollout without such evidence may cause a large spike in cases that may overwhelm our fragile healthcare system. Lives are in the balance, and a nuanced approach would serve us better.

The ideal is to find a way to maintain physical distance while increasing public transport capacity. If this cannot be done, research into the effectiveness of combined measures without physical distancing should be undertaken using simulations, proof of concept studies, and careful pilot testing. These kinds of studies have sufficient safety nets to ensure minimal risk to participants. Well-designed studies that might be able to show that combined measures work despite the decreased physical distance in public transport would be welcome. These may enable us to open up our economy faster without compromising safety.

As a physician, I always think about what is best for my patient. If a new intervention is proposed, I want to make sure the basis for the intervention is grounded on solid scientific evidence. As a scientist, I know that it is important to continue improving our interventions by looking at new approaches. This is a situation that we call “clinical equipoise,” in which there is a potential to benefit mankind, but there may also be inherent risks to the approach. To proceed safely, we keep the number of people who receive the initial intervention small. We incorporate good monitoring and safety checks in each study design. No widespread rollouts are done until we are sure it is safe. This is how science improves our lives. It can be done, and embracing innovation is an important part of the response to this pandemic.