From pandemic to endemic: Why COVID-19 may be here to stay

Since it first appeared in Asia, scientists have speculated that SARS-CoV-2, the virus that causes COVID-19 (coronavirus disease 2019), will not disappear. Similar to the seasonal influenza virus, it is expected to mutate over time—this has already become apparent as new “variants” of the virus have appeared. If correct, this suggests we will need to learn to live with the virus, and that it may eventually become endemic rather than pandemic.1

Endemic vs pandemic

The degree to which a virus spreads to cause disease can be classed into 3 different phases: endemic, epidemic, and pandemic.

Three regions of the earth with hotspots indicating amount of infected areas. Pandemic. Epidemic. Endemic.

  1. An endemic disease is restricted to a particular region or area and is constantly present but at manageable levels.2 For example, malaria is considered endemic in certain regions.
  2. An endemic disease becomes an epidemic when the number of people who are infected rises above levels that would be expected.2 Epidemics are also largely restricted to certain geographic regions or countries.
  3. A pandemic, on the other hand, occurs when an epidemic affects many more people and spreads across multiple countries or even entire continents.2 In a pandemic, the rate at which people become infected by a particular virus is exponential3—ie, a growing number of people are infected over a measure of time (eg, every day, week, month, etc).

COVID-19 is considered to be in its pandemic phase because the number of infections continues to increase and affect people worldwide.1 A February 2021 survey of over 100 scientists found that over half said they did not believe the virus could be eradicated, and 89% of them believe that COVID-19 will become endemic over time.1

How a COVID-19 endemic might be managed

By developing immunity against COVID-19—either through natural infection with the virus or vaccination—it is predicted that the disease will eventually become endemic. When most of the population is immune to a virus, so-called herd immunity can be achieved. The level of herd immunity that needs to be achieved to suppress transmission of a viral disease usually depends on how infectious it is in the first place—a virus that spreads easily and quickly requires higher levels of herd immunity.4 In the case of COVID-19, herd immunity would need to be achieved in at least 70% of the population to slow infection rates and reduce the spread of the virus, although this figure may be higher if new variants are shown to be more infectious.4

The role of vaccines in endemic disease

To stem the spread of COVID-19 and avoid serious illness and deaths, many countries have taken measures to control transmission and launched vaccination programs. Vaccines are one of the keys to ensuring that COVID-19 becomes endemic and stays that way as researchers have found that immunity from vaccination can be higher than immunity from natural infection.5 Levels of antibodies (the proteins developed by the body to fight harmful pathogens or substances) were also higher in people who previously had been infected with various variants of SARS-CoV-2 and later received a vaccine.6 Clinical studies have also found that moderate and severe disease that leads to hospitalization and even death could be reduced by up to 100% in adult trial participants.7 Other research shows that antibodies developed in response to a vaccine may target more variants of the virus that cause COVID-19 than those from natural immunity.8

As COVID-19 turns endemic and people return to a more normal way of living, without lockdowns or quarantines, widespread vaccination programs will continue to play a pivotal role. Antibodies developed in response to natural infection with SARS-CoV-2 tend to wane after 6-8 months.9 Antibodies from some vaccines against COVID-19 also appear to wane by 50% over 3 months,10 but studies have shown improved levels of protection when booster doses are used. Longer term immunity against the virus is still being explored.11,12

COVID-19 and seasonal influenza

Companies are also working on solutions to provide a single shot to vaccinate against influenza and COVID-19 at the same time. Such developments will further reduce the disease burden, expedite mass vaccination programs, and may help with speedier adaptations of vaccines to match new variants of a pathogen.

For more information about COVID-19 and seasonal influenza, visit our Areas of Research.

 

Relegating COVID-19 from a pandemic to a manageable endemic disease will require the commitment of global communities and the pharmaceutical industry. This is particularly important as the vaccines of the future will need to be flexible and adaptable to address multiple variants of the virus as they appear over time. In parallel, the need for consistent production and supply, along with equitable access and distribution of vaccines, must be adequately addressed.

  1. Phillips N. Nature. 2021;590(7846):382–384.
  2. Epidemic disease occurrence. Centers for Disease Control and Prevention. Available at: https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section11.html [Accessed 27 Aug 2021].
  3. Ma J. Infect Dis Model. 2020;5:129–141.
  4. D’Souza G, et al. What is herd immunity and how can we achieve it with COVID-19? Johns Hopkins Bloomberg School of Public Health. Available at: https://www.jhsph.edu/covid-19/articles/achieving-herd-immunity-with-covid19.html [Accessed 27 Aug 2021].
  5. Assis R, et al. BioRxiv. 2021. doi:10.1101/2021.04.15.440089.
  6. Leier HC, et al. MedRxiv. 2021. doi:10.1101/2021.04.25.21256049.
  7. U.S. clinical trial results show Novavax vaccine is safe and prevents COVID-19. National Institutes of Health. Available at: https://www.nih.gov/news-events/news-releases/us-clinical-trial-results-show-novavax-vaccine-safe-prevents-covid-19 [Accessed 27 Aug 2021].
  8. Greaney AJ, et al. Sci Transl Med. 2021;13(600).
  9. COVID-19 natural immunity. World Health Organization. Available at: href="https://apps.who.int/iris/rest/bitstreams/1346855/retrieve [Accessed 27 Aug 2021].
  10. Vaccine antibody levels start to wane at around 2-3 months. University College London. Available at: https://www.ucl.ac.uk/news/2021/jul/vaccine-antibody-levels-start-wane-around-2-3-months [Accessed 27 Aug 2021].
  11. Centers for Disease Control and Prevention. Effectiveness of a third dose of mRNA vaccines against COVID-19–associated emergency department and urgent care encounters and hospitalizations among adults during periods of Delta and Omicron variant predominance. 2022;71(4);139–145.
  12. Accorsi EK, et al. Association between 3 doses of mRNA COVID-19 vaccine and symptomatic infection caused by the SARS-CoV-2 Omicron and Delta variants. JAMA. 2022;327(7):639-651.
Additional reading

Additional reading

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