COVID-19 will probably become endemic – here’s what that means
Waning immunity
In diseases that give permanent immunity after infection, each new child born is susceptible after the immunity obtained from the mother wears off. This is why childhood infections such as measles are endemic in many parts of the world where the birth rate is high enough.
In diseases that only give temporary immunity through natural infection, people lose that immune protection to become susceptible again. A virus or bacteria can also evade the immune memory by mutation so that people with immunity to an older strain will become susceptible to the new version of the disease. Influenza is aprime example.
We don’t yet know how long immunity from infection from COVID-19 will last, or how good vaccines will be at protecting people. But other coronaviruses that are endemic in the human population, such as those that cause colds, only confer temporary immunity ofabout one year.
Another important point is that people with immunity, whether from infection or vaccination, are rarely evenly distributed throughout a community or country, let alone the world. Certainly in the case of COVID-19, there are areas where the infection has spread more intensively and areas that have been relatively spared. Without even distribution, there is no population immunity even if enough people have been vaccinated to meet the predicted necessary threshold.
In these cases, the average R can be low enough that the infection is under control, but in the unprotected pockets it will be well above 1. This leads to localized outbreaks and allows the disease to remain endemic. It continues to spread from place to place, seeded by a few locations where population density and interaction are high enough, and protection low enough, to sustain transmission.
How we respond
How we deal with COVID-19 once it becomes endemic will depend on how good our vaccines and treatments are. If they can protect people from the most severe outcomes, the infection will become manageable. COVID-19 will then be like several other diseases that we have learned to live with and many people will experience during their lives.
Depending on whether immunity – either from natural infection or from vaccination – is permanent or temporary, we may need yearlyvaccine updatesto protect us (like influenza). Or it could be controlled by vaccination at some optimal age (like many childhood infections).
If vaccines not only prevent clinical disease but also strongly reduce transmission and confer long-lasting immunity, we can envisage other scenarios, such as the potential eradication of the disease. But realistically this is unlikely. Eradication is notoriously difficult, even for diseases for which we have almost perfect vaccines and permanent immunity. Endemic disease is therefore the most likely outcome.
This article is republished fromThe ConversationbyHans Heesterbeek, Professor of Theoretical Epidemiology,Utrecht Universityunder a Creative Commons license. Read theoriginal article.
Story byThe Conversation
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