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What is a superspreader event?

This article was published on
July 19, 2021

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A superspreader event occurs when a single infection spreads among attendees at a gathering, resulting in an unusually large outbreak at once. This mode of transmission has been observed with the severe acute respiratory syndrome (SARS-CoV) epidemic, Middle East respiratory syndrome (MERS-CoV), Ebola, smallpox, tuberculosis, and the COVID-19 pandemic. 

A superspreader event occurs when a single infection spreads among attendees at a gathering, resulting in an unusually large outbreak at once. This mode of transmission has been observed with the severe acute respiratory syndrome (SARS-CoV) epidemic, Middle East respiratory syndrome (MERS-CoV), Ebola, smallpox, tuberculosis, and the COVID-19 pandemic. 

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What our experts say

A superspreader event occurs when a single infection spreads among attendees at a gathering, resulting in an unusually large outbreak at once. This mode of transmission has been observed with the severe acute respiratory syndrome (SARS-CoV) epidemic, Middle East respiratory syndrome (MERS-CoV), Ebola, smallpox, tuberculosis, and the COVID-19 pandemic. 

Documented superspreader events have occurred in a variety of settings, from family gatherings, funerals, and weddings, to corporate conferences, political ceremonies, and cruise ships. What is considered an unusually high number of infections varies by disease, therefore, scientists lack a standard set of criteria to define an event as a “superspreader.” However, there are some key, common ingredients among superspreader events: 

  1. Indoor spaces without adequate ventilation are high risk areas for virus droplets to circulate and cause infection. 
  2. Certain activities, such as choir practices or exercise classes, generate more airborne droplets. 
  3. Gatherings where the majority of attendees are unmasked are more likely to have poor control over infection sources. 
  4. Prolonged periods of contact increase exposure to droplets and the risk of transmission. 

Measures to minimize and control infection transmission include: 

  1. Closing or restricting the capacity of indoor spaces and gatherings.
  2. Holding gatherings outdoors. 
  3. Limiting the number of attendees at an event. 
  4. Requiring attendees to wear a mask correctly. 
  5. Mandating social distance between attendees to at least 6 feet. 
  6. Isolating for 14 days after close contact (within 6 feet for at least 15 minutes) of someone with COVID-19, or 7 days after a negative test (taken at least 5 days after the day of exposure). 
  7. Monitoring for known symptoms common to people with the infection for 2-14 days after potential exposure, and isolating accordingly if symptoms develop. 

While implementing regulations can help reduce risk, policy makers face the challenging act of balancing the economic and societal consequences of public health safety measures. As societies progress from state-of-emergency lockdowns and more people become vaccinated, superspreader events will likely lead to a larger percentage of infections.  

Context and background

Superspreader events have risen to attention as important contributors to COVID-19 transmission. Lately, experts have been concerned that international events, such as the recent Euro 2020 soccer tournament and upcoming Tokyo Olympics, are responsible for upticks in infection rates. 

Despite the progress of vaccination campaigns, Dr. Hans Henri P. Kluge, the World Health Organization (WHO) Regional Director for Europe, noted that only 24% of the European population was fully vaccinated. Prompting his statement on July 1st was the first increase in the number of COVID-19 cases in the WHO European Region after a 10-week period of decline. Crowds gathering to watch the soccer games in stadiums and at local establishments may have advanced rising COVID-19 infection rates in Europe. According to the WHO’s weekly COVID-19 epidemiological update on July 6th, the “European Region reported a sharp increase in incidence (30%)” compared to the previous week. 

Two weeks from the start of the Games, Tokyo Olympic organizers and Olympic officials decided to bar local spectators from attending several venues in response to increasing COVID-19 infections in Japan. The country’s fourth state of emergency was declared and began on July 12th. It will take effect throughout the Olympics, until its end on August 8th. 

Resources

  1. What Are ‘Superspreader’ Events and Why Should You Avoid Them? (Cleveland Clinic)
  2. Superspreading drives the COVID pandemic - and could help to tame it (Nature)
  3. What is a Superspreader Event? (Massachusetts General Hospital
  4. Tracking the White House Coronavirus Outbreak (The New York Times)
  5. SARS-CoV-2 (COVID-19) superspreader events (Journal of Infection)
  6. When to Quarantine (Centers for Disease Control and Prevention)
  7. Statement – COVID-19: The stakes are still high (World Health Organization)
  8. Crowds for European Championship soccer games are driving infections, the W.H.O. says (The New York Times)
  9. Weekly epidemiological update on COVID-19 - 6 July 2021 (World Health Organization)
  10. Tokyo Olympics: Spectators also barred from outlying venues (The Associated Press)
  11. Tokyo Olympics Bars Spectators as Japan Declares Covid-19 State of Emergency (The Wall Street Journal)
  12. Tokyo enters fourth COVID-19 state of emergency as Olympics loom (The Japan Times)

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