Social distancing;

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 can people with a respiratory virus such as Covid-19 be contagious even when they don’t cough or sneeze?

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

Couple of factors likely play a role in the transmission of respiratory viruses such as Covid-19 even in the absence of respiratory symptoms: 1. Generation of small droplets through everyday activities such as talking and breathing; 2. Presence of infectious virus in the respiratory tract before onset of symptoms.1-4

Small droplet generation during every day activity: Normal human speech and breathing can yield small particles or droplets that are too small to see by naked eye but are perfectly capable of serving as vehicles for aerial transport (more like hot air balloons than 737’s!) of a variety of communicable respiratory pathogens. 1  These small particles are believed to originate from the mucosal layers coating the respiratory tract as well as from vocal cord adduction and vibration within the larynx.1

In some cool experiments involving normal volunteers,1 the rate of particle emission during normal human speech positively correlated with the loudness of voice, ranging from 1-50 particles/second, irrespective of the language spoken (English, Spanish, Mandarin, or Arabic).  Perhaps, equally intriguing was identification of “speech superemitters”, consistently releasing an order of magnitude more particles than other participants.

Simply counting out loud has been associated with around 2-10 times as many total particles emitted as a single cough, 2 and the percentage of airborne droplet nuclei generated by singing is several times more than that emitted during normal talking and more like that of coughing! 3 Given, these observations, perhaps, the unfortunate outbreak of Covid-19 among members of a church choir in state of Washington 5 is not totally unexpected.

Presence of infectious virus in persons without symptoms:  An estimated 18% to 75% of patients testing positive for Covid-19 have no symptoms. This of course means that irrespective of whether symptoms ever develop, persons with Covid-19 may serve as a source of infection, by just breathing, talking, or singing when around susceptible people.

For these reasons, social distancing and wearing of masks during a pandemic makes sense!

Bonus Pearl: Did you know that infectious viral particles can be recovered from 40% of breath samples of patients with influenza? 6

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 References

  1. Asadi S, Wexler AS, Cappa CD, et al. Aerosol emission and superemission during human speech increase with voice loudness. Scientific Reports 2019;9:2348. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6382806/
  2. Loudon RG, Roberts RM. Droplet expulsion from the respiratory tract. Am Rev Resp Dis 1967;435-42. https://doi.org/10.1164/arrd.1967.95.3.435
  3. Loudon RG, Roberts MR. Singing and the dissemination of tuberculosis. Am Rev Resp Dis 1968;98:297-300. DOI: 10.1164/arrd.1968.98.2.297 https://www.atsjournals.org/doi/abs/10.1164/arrd.1968.98.2.297?journalCode=arrd
  4. Lai KM, Bottomley C, McNerney. Propagation of respiratory aerosols by the Vuvuzela. PLoS One 2011;6:e20086. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3100331/
  5. Read R. A choir decided to go ahead with rehearsal. Now dozens of members have COVID-19 and two are dead. Los Angeles Times March 29, 2020. https://www.latimes.com/world-nation/story/2020-03-29/coronavirus-choir-outbreak
  6. Yan J, Grantham M, Pantelic J, et al. Infectious virus in exhaled breath of symptomatic seasonal influenza cases from a college community. PNAS 2018;115:1081-1086 https://www.pnas.org/content/115/5/1081

Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. 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 can people with a respiratory virus such as Covid-19 be contagious even when they don’t cough or sneeze?