Here’s the scientific reason we need them
CLINICAL MATTERS
Few things are currently as controversial as face shields. With the Philippines being one of the few countries in the world that advocate its use, the face shield has become a hot button topic and reaped a lot of scorn from politicians and netizens alike. In this column, we examine the science behind face shields and whether it makes sense to continue using them as we move toward the new normal.
Is there any scientific evidence to support the use of face shields? Yes, there is a lot of data. Face shields have traditionally been used by medical personnel as part of personal protective equipment (PPE). Standard PPE can include a face mask, a face shield or goggles, gown, coveralls, gloves, booties, and a hair cap depending on the level of risk. A face shield protects the eyes from splashes. It also serves as a second layer of protection for the face, especially if the mask being worn is not waterproof. Face shields are particularly useful when a pathogen can be transmitted through the eyes.
When the COVID-19 pandemic started, it became apparent that SARS-CoV-2 was a respiratory virus. This means that its main route of entry is through the nose and mouth as one inhales infectious droplets. Touching droplet-contaminated surfaces followed by touching the mouth, nostrils, or eyes is another pathway. Direct virus inoculation through the eyes when infectious droplets land on them has also been documented.
The use of face shields on top of masks in the Philippines was initially proposed as an extra layer of protection for people who were taking public transportation. The reasoning was that since masks were imperfect, an extra layer of protection was desirable. This followed the findings of a Lancet meta-analysis that eye protection decreased the risk of COVID-19 transmission by 78 percent. The same study showed that face masks reduced transmission by up to 85 percent, while physical distancing of at least one meter decreased transmission by 82 percent (https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31142-9/fulltext). By combining a mask with a face shield, eminent epidemiologist Dr. Antonio Dans calculated that the transmission risk of COVID-19 could be decreased by 93 percent (https://www.facebook.com/antonio.dans/posts/4012546835460387).
By combining a mask, a face shield, and maintaining a one-meter physical distance, transmission of COVID-19 can be reduced by 99 percent. Given the crowded nature of public transport and the inability of passengers to properly distance, the essence of these equations were codified into the HPAAC recommendation of “APAT Dapat,” which stands for: A – air circulation; P – physical distance of one meter or more; A – always wear mask and face shield; T – 30 minutes of interaction or less. These recommendations were eventually extended into other spaces as the
Philippine government adopted the recommendation of HPAAC on face shields.
A study published in the Journal of the American Medical Association showed that 12 out of 62 community health workers doing contact tracing in India contracted COVID-19 after visiting
5,880 homes with 222 positive COVID-19 cases while only wearing masks. When face shields were added, no further infections were documented in the 50 remaining uninfected individuals after they visited 18,228 homes with 2,682 positive COVID-19 cases
(https://jamanetwork.com/journals/jama/fullarticle/2769693).
When the Alpha variant first threatened the Philippines toward the end of December 2020, Malacañang decided to make face shields mandatory as a precaution against this new variant.
The Philippines succeeded in keeping cases low throughout the Christmas season despite increases in mobility. In the meantime, more data emerged that eye protection on top of masking might be important (https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(21)00040-9/fulltext)
When the combination of the Alpha and Beta wave finally hit in March 2021, new COVID-19 cases peaked at 15,280 in a day and subsided in April. As cases started to recede, a clamor to relax face shields came out of nowhere despite previous broad support from society. The contention was that this was not useful and there was no science that supported it. This was clearly an inaccurate assessment, but the general dislike for face shields fueled the call to scrap face shields.
Given this demand, the IATF asked the Technical Advisory Group (TAG) to reassess the evidence. The modified recommendation was to recommend but not mandate face shields for outside, non-crowded settings because these were relatively low risk.
Face shield use indoors, however, should remain compulsory. Meanwhile, the threat of the Delta variant was starting to emerge. The world looked in horror as India grappled with over 400,000 cases a day and 4,000 deaths a day. It also became apparent that Delta was much more transmissible and required only fleeting contact to infect someone. When the new recommendations on face shields were presented to the President, the emerging threat of Delta was coincidentally discussed in the same meeting. Sensing the danger that Delta posed to the Philippines, President Duterte decided to maintain compulsory face shields with face masks for both indoor and outdoor settings. This turned out to be a good decision in retrospect since this helped temper the peak of the Delta wave.
After peaking at 26,208 cases in September, COVID-19 cases have now decreased to below
2,000 a day. Face shield requirements have been eased to the original TAG recommendation for indoor and crowded settings and are no longer compulsory in most outdoor areas.
There are now, however, renewed calls to completely scrap these. The previous baseless assertion that there is no science supporting its use is being bandied anew.
Did face shields on top of face masks save lives? Without a doubt. A paper in the New England
Journal of Medicine prior to the widespread availability of vaccines explored the idea of “variolation” where infection with a low number of virus particles is less likely to result in severe disease (https://www.nejm.org/doi/full/10.1056/nejmp2026913).
Masks and additional layers like face shields can significantly reduce the number of virus particles that get through, such that even if an infection breaks through all these barriers, the resulting infection is likely to be mild. Face shields, along with masks, early lockdowns, and excellent care from our doctors and nurses all contributed to the low case fatality rate of the
Philippines. The population-adjusted death rate for our country 393 deaths per million (122nd in the world), which is nearly six times less than the death toll in the US (2,311 deaths per million, 16th in the world), despite our limited healthcare capacity.
What is the best way forward? While COVID-19 cases are currently low, there is always the risk that infections will spike anew, especially as mobility is increased and restrictions are relaxed.
Denmark, despite having over 82 percent of its eligible population vaccinated, has had to reimpose face masks in the light of a rapid rise in COVID-19 cases. The US earlier this year relaxed the mask mandate for fully vaccinated individuals but was forced to reinstate this when cases rose. As we transition into lower alert levels, a middle ground on relaxing the need for face shields (but not masks), at least for those who are fully vaccinated may be feasible. It is, however, not yet advisable to scrap face shields permanently. We should keep these ready in case a spike in cases results in a higher alert level requiring enhanced safety measures anew. We should keep all useful tools on the table, especially when it comes to saving Filipino lives.