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How long will the COVID-19 pandemic last? Three possible scenarios.

Early this week, researchers from the Center for Infectious Disease Research and Policy, at the University of Minnesota, released a report titled, The Future of the COVID-19 Pandemic: Lessons Learned from Pandemic Influenza.

In the report, the researchers argue that while the future course of COVID-19 still remains uncertain, analyses of comparative models from past pandemics have may help us understand how COVID-19 is likely to play out.

Specifically, analyses of past Influenza pandemics are likely to lead to the most accurate models given that:

  • Influenza, like SARS CoV-2 was a novel viral pathogen to which the global population had little to no immunity.

  • As with COVID-19, asymptomatic infection was a key contributor to the rapid spread.

  • The spread of both viruses predominantly was through airborne droplets.

Key points from observing the epidemiology of past influenza pandemics that may provide insight into the COVID-19 pandemic include the following. First, the length of the pandemic will likely be 18 to 24 months, as herd immunity gradually develops in the human population. This will take time, since limited serosurveillance data available to date suggest that a relatively small fraction of the population has been infected and infection rates likely vary substantially by geographic area. Given the transmissibility of SARS-CoV-2, 60% to 70% of the population may need to be immune to reach a critical threshold of herd immunity to halt the pandemic.

This may be complicated by the fact that we don’t yet know the duration of immunity to natural SARS-CoV-2 infection (it could be as short as a few months or as long as several years). Based on seasonal coronaviruses, we can anticipate that even if immunity declines after exposure, there may still be some protection against disease severity and reduced contagiousness, but this remains to be assessed for SARS-CoV-2. The course of the pandemic also could be influenced by a vaccine; however, a vaccine will likely not be available until at least sometime in 2021. And we don’t know what kinds of challenges could arise during vaccine development that could delay the timeline.

Second, there are several different scenarios for the future of the COVID-19 pandemic, and some of these are consistent with what occurred during past influenza pandemics. These can be summarized as follows and are illustrated in the figure below

Possible Scenarios

Adapted from CIDRAP, University of Minnesota

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 is especially relevant in countries such as India which do not have robust healthcare infrastructure.

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.

While the models developed in the study primarily apply to the health systems in the temperate northern hemisphere, much of the conclusions can apply to the global south as well. In fact, the magnitude of the impact may be far higher owing to the general lack of robust healthcare infrastructure and the co-existence of other co-morbidities such as TB in the region.