Sat. Sep 24th, 2022
Image of two women wearing both face masks and face shields.
enlarge A mask/shield combination provides better protection.

One of the biggest challenges of the COVID-19 pandemic is that we just don’t know what works against the SARS-CoV-2 coronavirus. Most of the scientific research into managing pandemics has focused on the flu virus, which is different from the coronavirus in many ways. The coronaviruses we do know about — SARS, MERS, and two common cold viruses — are quite different from each other.

We have no hard data on what works. Do we need two meters of social distancing or three? What types of face masks are most effective? We try to collect data on these issues as we implement them. So in a little bit of good news, we now have some data pointing to something that is effective: plastic face shields.

To the subcontinent!

The work was done in India and benefits from a public health program launched as the pandemic spread through that country. Workers in a research network in Chennai agreed to voluntarily go into isolation and then visit the families of those who tested positive for SARS-CoV-2 to explain things like quarantine, mask use, social distancing, and so on.

Before we get into what happened to these workers, let’s take a step back to admire these people. They agreed to leave their families behind to live in hotel rooms. They were kept completely isolated from their friends and peers – meals were delivered to their rooms and even their transport was a van with a steel partition to keep them isolated from their driver. All their direct contact with people was with people who were probably infected. While the families they visited were asked to wear masks and keep at least two meters away from health workers, compliance was erratic.

And although they were given gloves, surgical masks and alcoholic hand sanitiser, it took just two weeks for the first workers to develop symptoms. The program was suspended and all workers were tested for the virus. Ten of the 62 involved were infected. Together they had visited 5,880 homes and came into contact with a total of 222 people who eventually tested positive for the virus. Fortunately, the partitions in their transport worked and none of their drivers got infected.


When the program is restarted, an extra form of protection has been applied: a transparent plastic face shield. The health workers were also given ethanol to clean their shields between home visits. With those measures, workers visited an additional 18,228 homes, where 2,682 people eventually tested positive for the virus.

There were zero infections among the health workers.

It is entirely possible that the initial infection heightened the workers’ sense of caution when the program was restarted. But it’s not clear whether behavioral changes could be maintained over the course of 18,000 home visits. So the face shields are probably the cause of the critical difference.

The authors of the paper describing the results are not sure what the critical contribution was. The shield may have routed air around the face or prevented the face mask from becoming contaminated. It would also provide some protection for the eyes, which is a known route of infection. So there’s more we can learn here. But the results seem to be enough to indicate that high-risk individuals may benefit from using face shields.

JAMA, 2020. DOI: 10.1001/jama.2020.15586 (About DOIs).

Corrections: Minor change in title as people found it confusing. Fixed one mask/shield error.

By akfire1

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