Reevaluating the 6-Foot Rule: Efficacy and Challenges in COVID-19 Prevention

During the June 3, 2024, House Oversight Committee regarding the Coronavirus Pandemic, the 6-foot rule was again thrown into the spotlight, and questions about its appropriateness and effectiveness were raised. One of the Representatives questioned the continuation of advocating for 6 feet of social distancing after it was known the virus was aerosolized. This question exemplifies one of the underlying problems in our pandemic response—dividing the spread of respiratory pathogens into aerosols and large droplets.

Some critics of the 6-foot rule have pointed to the adverse impacts of social distancing on schools and businesses. However, social distancing was adopted by almost every industrialized nation, even Sweden. In most countries, including South Korea, Australia, Belgium, Germany, Greece, Italy, Netherlands, Portugal, and Spain, a social distance of 1.5 yards or meters was recommended. The US, Canada, and the UK chose 2 yards or meters. A few countries chose 1 meter of separation, but this is so close that accidental contact between individuals can occur.

Social distancing has been advocated by science dating back to the 1800s and most recently has been supported by the findings published in the Lancet by Chu and colleagues. They observed a strong association between the “proximity of the exposed individual with the risk of infection.” There was a 12.8% chance of transmission for distances less than 1 meter, which dropped to 2.6% for distances greater than 1 meter. The authors stated, “We found evidence of moderate certainty that current policies of at least 1-meter physical distancing are probably associated with a large reduction in infection and that distances of 2 meters might be more effective, as implemented in some countries.“ The researchers recommended implementing at least 1 meter of physical distancing and, if possible, 2 meters to mitigate the transmission of SARS-CoV-2 (the virus that causes COVID-19).

There is ample evidence that the 6-foot rule will help decrease spread, but with a highly infectious virus, it alone will not provide adequate protection. Here is why:

Most importantly, droplets are a type of medium similar to solid particles (particulate matter or PM) that can spread the virus. Both droplets and particles have a continuum of sizes, not just large ones and small ones. Particles up to 100 microns can aerosolize.
 
Breathing, talking, and singing can aerosolize particles. Smaller particles are generated deep in the lower airway, with larger particles in the upper airway. Breathing produces particle sizes below 0.8 microns, and speech produces additional particles up to 5 microns in size. The vast majority of the particles are less than 10 microns. Particles less than 1 micron have been observed to contain more SARS-CoV-2 viruses than larger particles.

Respiratory droplet aerosols can be highly infectious, decreasing their infectivity by approximately 10% every 20 minutes. However, the virus's survivability varies with relative humidity, and lower values decrease viral stability.

Air pollution from fuel combustion, such as car exhaust, produces fine particles (PM2.5) that can facilitate the spread of SARS-CoV-2 (the virus that causes COVID-19). Individuals living in regions with high PM2.5 levels are known to have higher COVID-19 death rates. As with small aerosols caused by droplets, these particles aerosolize and can spread much further than 6 feet.

Although the 6-foot rule will protect against large nonaerosolized particles, it will not afford the needed protection if one is exposed to a highly infectious airborne virus that spreads through the air. Because aerosols float in the air, ventilation is a key factor in their elimination. In highly ventilated indoor settings or outdoor venues, aerosolized particles will dissipate, but large particles will not. Thus, the 6-foot rule adds substantial protection if you do not have a mask and are outdoors. In highly ventilated indoor settings, the same may be true. This is why a CO₂ monitor is handy for measuring indoor ventilation. However, the safest option indoors or in crowded outdoor settings is wearing an N95 mask.

The answer regarding whether the 6-foot rule is effective is yes. But it makes sense and is appropriate only if indoor ventilation is also addressed. Not having safe indoor ventilation is one of the most significant failings of our pandemic response.


References

·US Congress. Committee on Oversight and Accountability. A Hearing with Dr. Anthony Fauci. 2154 Rayburn House Office Building. June 3, 2024. Accessed July 21, 2024. https://oversight.house.gov/hearing/a-hearing-with-dr-anthony-fauci/

·Daily Mail. Rep. Comer says he 'likes the idea' of Fauci being arrested. MSN.com. June 2020. Accessed July 21, 2024. https://www.msn.com/en-us/news/politics/top-gop-says-he-likes-the-idea-of-fauci-being-arrested/ss-BB1nGvwA.

·Shukman D. Coronavirus: Could social distancing of less than two metres work? BBC. June 32, 2020. Accessed July 21, 2024. https://www.bbc.com/news/science-environment-52522460.

Sweden hardens COVID curbs amid worries over Omicron. Reuters. Dec. 21, 2021. Accessed July 21, 2024. https://www.reuters.com/world/europe/sweden-tightens-covid-restrictions-cases-mount-2021-12-21/.

·Eldred SM. Coronavirus FAQ: How Do The Rules of 6 Feet And 15 Minutes Apply To The Delta Variant? NPR. Aug. 27, 2021. Accessed July 21, 2024. https://www.npr.org/sections/goatsandsoda/2021/08/27/1031753581/coronavirus-faq-how-does-the-6-feet-15-minutes-rule-apply-to-the-delta-variant.

·Chu DK, Akl EA, Duda S, et al; COVID-19 Systematic Urgent Review Group Effort (SURGE) study authors. Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis. Lancet. 2020;395(10242):1973-1987. doi:10.1016/S0140-6736(20)31142-9. https://pubmed.ncbi.nlm.nih.gov/32497510/.

·Harvard T.H. Chan School of Public Health. Air pollution linked with higher COVID-19 death rates. Accessed July 21, 2024. https://www.hsph.harvard.edu/news/hsph-in-the-news/air-pollution-linked-with-higher-covid-19-death-rates/.

·Lam V. Air pollution can increase the risk of COVID infection and severe disease – a roundup of what we know. The Conversation. Accessed July 21, 2024. https://theconversation.com/air-pollution-can-increase-the-risk-of-covid-infection-and-severe-disease-a-roundup-of-what-we-know-201813.

·Oswin HP, Haddrell AE, Otero-Fernandez M, et al. The dynamics of SARS-CoV-2 infectivity with changes in aerosol microenvironment. Proc Natl Acad Sci U S A. 2022;119(27). doi:10.1073/pnas.2200109119. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9271203/.

·Morawska L. Health Watch USA Conference. Sept. 14, 2022.Accessed July 21, 2024. https://www.healthwatchusa.org/conference2022/2022Conference_downloads/05-Morawska-20220914-Webinar.pdf.

·Morawska L, Johnson GR, Ristovski ZD, et al. Size distribution and sites of origin of droplets expelled during expiratory activities. J Aerosol Sci. 2009;40(3):256-269. doi:10.1016/j.jaerosci.2008.11.002. https://www.sciencedirect.com/science/article/abs/pii/S0021850208002036.

·Santarpia JL, Herrera VL, Rivera DN, et al. The Infectious Nature of Patient-Generated SARS-CoV-2 Aerosol. medRxiv. July 21, 2020. Accessed July 21, 2024. doi:10.1101/2020.07.13.20041632. https://www.medrxiv.org/content/10.1101/2020.07.13.20041632v2.

·Fox M. Six-foot social distancing rule misses bigger risks, MIT experts say. CNN. April 27, 2021. Accessed July 21, 2024. https://www.cnn.com/2021/04/27/health/covid-spread-inside-wellness/index.html.