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US Experts Predict Waves of COVID-19 Lasting Into 2022
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Mark Mascolini
Get ready for multiple waves of COVID-19 into 2022, warns a US group of public health and infectious disease (ID) specialists [1]. Using pandemic influenza as a model, the group figures that the COVID-19 pandemic will probably last at least another18 to 24 months.
Pandemic COVID-19 "caught the global community off guard, and its future course is still highly unpredictable," write experts working with the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota. Other authors of this report come from the Harvard TH Chan School of Public Health and Tulane University School of Public Health and Tropical Medicine.
The Public Health/ID team foresees a continuing epidemic until 60% to 70% of the global population attains immunity against SARS-CoV-2, the virus that causes COVID-19. Cases of infection, they predict, "may come in waves of different heights . . . and in different intervals."
To predict the course of the COVID-19 epidemic, the researchers reject comparisons with two other coronavirus diseases, SARS (caused by SARS-CoV-1) and MERS (caused by MERS-CoV) because their epidemiology differs too much from COVID-19. The best model for the COVID-19 epidemic, they propose, could come from pandemic influenza. Four flu pandemics have ripped across the globe since 1900, in 1918-1919, 1957, 1968, and 2009-2010.
COVID-19 and pandemic flu have several similarities, the Public Health/ID team notes: (1) little to no pre-existing immunity in the population, (2) respiratory spread through large droplets and smaller aerosols, (3) asymptomatic transmissions, and (4) ability to infect millions of people around the world.
But several differences between COVID-19 and pandemic flu make modeling COVID-19 on flu tricky: (1) Longer incubation with COVID-19 (about 5 days versus 2 with flu) allows COVID-19 to move silently. (2) The fraction of asymptomatic people appears larger with COVID-19 than with flu. (3) SARS-CoV-2 may have more presymptomatic shedding than pandemic influenza A.
All the just-listed factors influence how transmissible SARS-CoV-2 and influenza are. Epidemiologists gauge transmissibility as R0, the average number of new infections caused by a single person in a wholly susceptible population. Researchers estimate the R0 for COVID-19 in China at 2.0 to 2.5, whereas the R0 for pandemic flu has been lower: 1.8 for 1918 and 1968, 1.65 for 1957, and 1.46 for 2009-2010. An outbreak begins to decline only when R0 falls below 1.0. In other words pandemic influenza viruses have been less transmissible than SARS-CoV-2.
Pandemic influenza has come in waves, with peaks that may wane without human intervention. And flu pandemics usually were not much influenced by vaccination campaigns. Analyzing the epidemiology of past influenza pandemics—and trying to balance all the noted similarities and differences—led the Public Health/ID group to suggest what may happen with the current COVID-19 pandemic.
First, the COVID-19 pandemic will probably last 18 to 24 months. Second, the pandemic will not disappear until 60% to 70% of the global population becomes immune. And third, "depending on control measures and other factors, cases may come in waves of different heights (with high waves signaling major impact) and in different intervals." The authors propose 3 possibilities for the COVID-19 wave pattern:
Scenario 1: The first COVID-19 wave in spring 2020 gives way to a series of smaller waves that eventually peter out sometime in 2021.
Scenario 2: The spring 2020 wave is followed by a larger wave in the fall or winter and 1 or 2 smaller waves in 2021.
Scenario 3: The spring 2020 wave gives way to a "slow burn" of ongoing transmission without a clear wave pattern and lasting into 2022.
Whichever wave pattern develops, the researchers caution that "we must be prepared for at least another 18 to 24 months of significant COVID-19 activity, with hot spots popping up
periodically in diverse geographic areas."
The authors make several recommendations, included pointed advice to political leaders: "Risk communication messaging from government officials should incorporate the concept that this pandemic will not be over soon and that people need to be prepared for possible periodic resurgences of disease over the next 2 years."
Reference
1. Moore KA, Lipsitch M, Barry JM, Osterholm. ¬¬CIDRAP. Center for Infectious Disease Research and Policy. Part 1: The future of the COVID-19 pandemic: lessons from pandemic influenza. https://www.cidrap.umn.edu/sites/default/files/public/downloads/cidrap-covid19-viewpoint-part1_0.pdf
Scenario 1: The first wave of COVID-19 in spring 2020 is followed by a series of repetitive smaller waves that occur through the summer and then consistently over a 1- to 2-year period, gradually diminishing sometime in 2021. The occurrence of these waves may vary geographically and may depend on what mitigation measures are in place and how they are eased. Depending on the height of the wave peaks, this scenario could require periodic reinstitution and subsequent relaxation of mitigation measures over the next 1 to 2 years.
•Scenario 2: The first wave of COVID-19 in spring 2020 is followed by a larger wave in the fall or winter of 2020 and one or more smaller subsequent waves in 2021. This pattern will require the reinstitution of mitigation measures in the fall in an attempt to drive down spread of infection and prevent healthcare systems from being overwhelmed. This pattern is similar to what was seen with the 1918-19 pandemic (CDC 2018). During that pandemic, a small wave began in March 1918 and subsided during the summer months. A much larger peak then occurred in the fall of 1918. A third peak occurred during the winter and spring of 1919; that wave subsided in the summer of 1919, signaling the end of the pandemic. The 1957-58 pandemic followed a similar pattern, with a smaller spring wave followed by a much larger fall wave (Saunders-Hastings 2016). Successive smaller waves continued to occur for several years (Miller 2009). The 2009-10 pandemic also followed a pattern of a spring wave followed by a larger fall wave (Saunders-Hastings 2016).
•Scenario 3: The first wave of COVID-19 in spring 2020 is followed by a "slow burn" of ongoing transmission and case occurrence, but without a clear wave pattern. Again, this pattern may vary somewhat geographically and may be influenced by the degree of mitigation measures in place in various areas. While this third pattern was not seen with past influenza pandemics, it remains a possibility for COVID-19. This third scenario likely would not require the reinstitution of mitigation measures, although cases and deaths will continue to occur.
Whichever scenario the pandemic follows (assuming at least some level of ongoing mitigation measures), we must be prepared for at least another 18 to 24 months of significant COVID-19 activity, with hot spots popping up periodically in diverse geographic areas. As the pandemic wanes, it is likely that SARS-CoV-2 will continue to circulate in the human population and will synchronize to a seasonal pattern with diminished severity over time, as with other less pathogenic coronaviruses, such as the betacoronaviruses OC43 and HKU1, (Kissler 2020) and past pandemic influenza viruses have done.
Whichever scenario the pandemic follows (assuming at least some level of ongoing mitigation measures), we must be prepared for at least another 18 to 24 months of significant COVID-19 activity, with hot spots popping up periodically in diverse geographic areas. As the pandemic wanes, it is likely that SARS-CoV-2 will continue to circulate in the human population and will synchronize to a seasonal pattern with diminished severity over time, as with other less pathogenic coronaviruses, such as the betacoronaviruses OC43 and HKU1, (Kissler 2020) and past pandemic influenza viruses have done.
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