Masks

Why is the Delta variant of SARS-CoV-2 increasingly becoming a “variant of concern” in the current Covid-19 pandemic?

FA Manian MD, MPH, , , , , , , , , , , , , , , Leave a comment

The Delta variant (B.1.617.2, formerly India variant) has become an increasingly prevalent strain of SARS-Cov-2 causing Covid-19 in many countries outside of India, including the United States and United Kingdom, particularly affecting younger unvaccinated persons.  Several features of the Delta variant are of particular concern. 1-7

  1. Delta virus appears to be more transmissible when compared to previously emerged variant viruses. Data from new Public Health England (PHE) research suggests that the Delta variant is associated with a 64% increased risk of household transmission compared with the Alpha variant (B.,1.1.7, UK variant) and 40% more transmissibility in outdoors. 1,8  
  2. Delta virus is also associated with a higher rate of severe disease, doubling the risk of hospitalization based on preliminary data from Scotland. In vitro, it replicates more efficiently than the Alpha variant with higher respiratory viral loads.5
  3. Delta virus may also be associated with reduced vaccine effectiveness with increased vaccine breakthroughs. One study found that Delta variant is 6.8-fold more resistant to neutralization by sera from Covid-19 convalescent and mRNA vaccinated individuals.5 Fortunately, a pre-print study released by PHE in May 2021 found that 2 doses of the Pfizer vaccine were still 88% effective against symptomatic infection with Delta variant  (vs 93% for the Alpha variant) and 96% effective against hospitalization; 1 dose was only 33% effective against symptomatic disease (vs 50% for the Alpha variant). 6   Two doses of Astra Zeneca vaccine were 60% effective against symptomatic disease from the Delta variant.8 
  4. Aside from its somewhat unique epidemiologic features, Covid-19 caused by Delta variant seems to be behaving differently (starting out as a “bad cold” or “off feeling”), with top symptoms of headache, followed by runny nose and sore throat with less frequent fever and cough; loss of sense of smell was not common at all based on reported data to date.1

What the Delta variant reminds us is, again, the importance of vaccination, masks and social distancing. The pandemic is still with us!

Bonus Pearl: Did you know that, on average, a Delta variant-infected person may transmit it to 6 other contacts (Ro~6.0) compared to 3 others (Ro~3) for the original SARS-CoV-2 strains found during the early part of the pandemic?1

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References

  1. https://www.bbc.com/news/health-57467051
  2. Knodell R. Health Advisory: Emergence of Delta variant of coronavirus causing Covid-19 in USA. Missouri Department of Health & Senior Services. 23 June, 2021. https://health.mo.gov/emergencies/ert/alertsadvisories/pdf/update62321.pdf
  3. Kupferschmidt K, Wadman M. Delta variant triggers new phase in the pandemic. Science 25 June 2021; 372:1375-76. https://science.sciencemag.org/content/sci/372/6549/1375.full.pdf
  4. Sheikh A, McMenamin J, Taylor B, et al. SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness. Lancet 2021; 397:2461-2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8201647/
  5. Mlcochova P, Kemp S, Dhar MS, et al. Sars-Cov-2 B.1.617.2 Delta variant emergence and vaccine breakthrough. In Review Nature portfolio, posted 22 June, 2021. https://www.researchsquare.com/article/rs-637724/v1
  6. Bernal JL, Andrews N, Gower C, et al. Effectiveness of Covid-19 vaccines against the B.1.617.2 variant. MedRxiv, posted May 24, 2021. https://www.medrxiv.org/content/10.1101/2021.05.22.21257658v1 vaccine efficacy
  7. Allen H, Vusirikala A, Flannagan J, et al. Increased household transmission of Covid-19 cases associatd with SARS-Cov-2 variant of concern B.1.617.2: a national case control study. Public Health England. 2021. https://khub.net/documents/135939561/405676950/Increased+Household+Transmission+of+COVID-19+Cases+-+national+case+study.pdf/7f7764fb-ecb0-da31-77b3-b1a8ef7be9aa  Accessed June 27, 2021.
  8. Callaway E. Delta coronavirus variant: scientists brace for impact. Nature. 22 June 2021. https://www.nature.com/articles/d41586-021-01696-3 

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis or its affiliate healthcare centers, Mass General Hospital, Harvard Medical School or its affiliated institutions. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author.

Why is the Delta variant of SARS-CoV-2 increasingly becoming a “variant of concern” in the current Covid-19 pandemic?

Beyond masks and hand hygiene, what factors impact transmission of Covid-19 in indoor gatherings?

FA Manian MD, MPH, , , , , , , , , , , , , , , Leave a comment

Aside from factors specific to the source individual (eg, viral load in exhaled air, “superspreader” features, etc…) and host characteristics (eg, older age, obesity, immunocompromised state), transmission of SARS-CoV-2 in indoor settings may be impacted by several factors, including social distancing, ventilation of rooms/ direction of airflow, room occupancy, exposure time and higher risk activities, such as eating, talking loud, heavy breathing during exercise, laughing, coughing and sneezing. 1-4

  1. Physical distance from infected individuals. Although a “safe” distance of 6 feet has often been cited, increasing evidence suggests that SARS-CoV-2 may be spread not only by larger droplets but also by airborne route (ie, beyond 6 feet or shortly after an infected person leaves the area). In fact, 8 of 10 studies on horizontal droplet distance have reported droplets traveling more than 6 feet (2 meters), some cases up to 26 feet (8 meters), and 1 study documented virus at 13 feet (4 meters). Transmission beyond 6 feet is not surprising since even as early as 1948 beta streptococci were found 9.5 feet from 10% of people who were infected!1
  2. Quality of ventilation and direction of airflow in the room. Poorly ventilated rooms would be expected to have more potentially infectious droplets in the air for longer periods of time, even after an infected person leaves the area.
  3. Room occupancy. The higher the occupancy the more likely to have exhaled contaminated air from 1 or more infected persons (symptomatic or asymptomatic) with exposure of susceptible hosts.
  4. Exposure time. Exposure to contaminated air in the room even for a relatively short period of time (ie, >5-15 minutes) is likely to increase the risk of transmission.
  5. Activity of infected individual. Many activities such as singing, speaking loudly, eating, laughing, breathing heavily during exercise, coughing and sneezing may increase risk of Covid-19 transmission in indoor settings.

Recall that over one-half of Covid-19 transmissions are due to asymptomatic individuals.5 In this setting and in the presence of factors discussed above, it’s easy to see how transmission of Covid-19 in indoor settings can occur readily, possibly explaining cases without apparent source.

Bonus Pearl: Did you know that the odds of Covid-19 transmission may be 18.7 times greater indoors compared to open-air environment and the odds of superspreading event in closed environments may be 32.6 times higher?4

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References

  1. Bahl P, Doolan C, de Silva C, et al. Airborne or droplet precautions for health workers treating coronavirus disease 2019? J Infect Dis 2020. Published online April 16, 2020. https://pubmed.ncbi.nlm.nih.gov/32301491/
  2. Jones NR, Quereshi Z, Temple RJ, et al. Two metres or one: what is the evidence for physical distancing in covid-19? BMJ 2020;370:m3223. https://www.bmj.com/content/370/bmj.m3223/rr-18
  3. Johansson MA, Quandelacy TM, Kada S, et al. SARS-CoV-2 transmission from people without COVID-19 symptoms. JAMA Network open. 2021;4():e2035057. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2774707?utm_source=For_The_Media&utm_medium=referral&utm_campaign=ftm_links&utm_term=010721
  4. Nishiura H, Oshitani H, Kobayashi T, et al. Closed environments facilitate secondary transmission of coronavirus disease 2019 (COVID-19). MedRxiv 2020. https://www.medrxiv.org/content/10.1101/2020.02.28.20029272v2.full.pdf
  5. Leclerc QJ, Fuller NM, Knight LE,e tal. What settings have been linked to SARS-CoV-2 transmission clusters? Wellcome Open Research October, 2020. https://wellcomeopenresearch.org/articles/5-83    

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis or its affiliate healthcare centers. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

Beyond masks and hand hygiene, what factors impact transmission of Covid-19 in indoor gatherings?

How effective are face masks in reducing transmission of Covid-19?

FA Manian MD, MPH, , , , , , , , , , , Leave a comment

Overall, review of data to date suggests that face masks are quite effective in reducing the transmission of coronaviruses, including SARS-CoV-2, the cause of Covid-19. A Lancet 2020 meta-analysis involving over 12,000 subjects, found that transmission of coronaviruses (SARS-CoV-2, SARS and MERS) was reduced with face masks by 85% (adjusted O.R. 0.15, 95%CI 0.07-0.34).1

More specific to Covid-19, a study from Mass General Brigham hospitals found a significant drop in healthcare worker (HCW) SARS-CoV-2 PCR positivity rate from 21.3% to 11.5% following adoption of universal masking of HCWs and patients.2

An U.S. epidemiologic survey of 2,930 unique counties plus New York City found mandating face mask use in public was associated with a significant decline in the daily Covid-19 growth rate. 3 It was estimated that more than 200,000 Covid-19 cases were averted by May 22, 2020 as a result of the implementation of these mandates.

Another 2020 meta-analysis involving 21 studies reported an overall efficacy of masks (including surgical and N-95 masks) of 80% in healthcare workers and 47% in non-healthcare workers for respiratory virus transmission (including SARS, SARS-CoV-2 and influenza).4

A criticism of above reports has been their primarily retrospective nature. A randomized-controlled Danish study found a statistically insignificant 20% reduction in incident SARS-CoV-2 infection among mask wearers (5,6).    Despite its randomized-controlled design, this study had several limitations, including relatively low transmission rate in the community and lack of universal mask wearing in public during the study period. In addition, less than one-half of participants in the mask group reported adherence to wearing masks, and there was no assurance that masks were worn correctly when they did wear them. 

At most, this study suggests that it’s not enough for the uninfected to wear masks; the infected—often with little or no symptoms— should also wear them to help curb the pandemic.

So please do your part and tell your friends and family members to do the same by masking up while we are at war with Covid-19!

Bonus Pearl: Did you know that universal wearing of masks in the public in response to a respiratory virus pandemic is nothing new?  It was adopted as far back as 100 years ago during the 1918 Spanish influenza pandemic!

References

  1. Chu DK, Akl EA, Duda S, et al. 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: 1973-87. https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(20)31142-9.pdf
  2. Wang X, Ferro EG, Zhou G, et al. Association between universal masking in a health care system and SARS-CoV-2 positivity among health care workers. JAMA 2020;324:703-4. https://jamanetwork.com/journals/jama/fullarticle/2768533
  3. Lyu W, Wehby GL. Community use of face masks and COVID-19: evidence from a natural experiment of state mandates in the US. Health Affairs 2020;39: July 16. https://www.healthaffairs.org/doi/full/10.1377/hlthaff.2020.00818
  4. Liang M, Gao L, Cheng Ce, et al. Efficacy of face mask in preventing respiratory virus transmission: A systematic review and meta-analysis. Travel Med Infect Dis 2020;36:1-8. https://pubmed.ncbi.nlm.nih.gov/32473312/ 
  5. Bundgaard H, Bundgaard JS, Tadeusz DE, et al. Effectiveness of adding a mask recommendation to other public health measures to prevent SARS-CoV-2 infection in Danish mask wearers. Ann Intern Med 2020; November 18. https://pubmed.ncbi.nlm.nih.gov/33205991/
  6. Frieden TR Cash-Goldwasser S. Of masks and methods. Ann Intern Med 2020; November 18. https://www.acpjournals.org/doi/10.7326/m20-7499

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Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis or its affiliate healthcare centers. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

How effective are face masks in reducing transmission of Covid-19?