Amid the daily barrage of new data on Covid-19, sometimes the most basic principles of the disease manage to evade the headlines. I recognize this by the types of questions I hear on a regular basis from friends, family, and even my co-workers at the hospital. Let’s address three of the most common concerns.
1. Since immunity to the novel coronavirus may not last long, doesn’t the virus need to be eradicated in order for the pandemic to end?
Humans generally become immune to a pathogen after immunization or recovery from an infection. Depending on the particular disease or vaccine as well as host characteristics such as the age and health of the individual, immunity can last a lifetime or may be short-lived. Moreover, immunity is not an ‘either/or’ process. Our immunity to different pathogens doesn’t just suddenly switch off. Instead, it wanes over time.
It is true that a person’s immunity to the novel coronavirus, SARS-CoV-2, probably only lasts a few months to a few years. It is also true that outbreaks of two other coronaviruses earlier this century, SARS and MERS, were indeed contained, although not technically eradicated. However, the other four known human coronaviruses, HCoV-229E, -NL63, -OC43, and -HKU1, are considered endemic. These viruses, which have been around longer than the other three, are continuously circulating through the population and typically cause no more symptoms than the common cold.
Interestingly, there is historical evidence that the four endemic coronaviruses were likely the cause of pandemics, or at least epidemics, in the past. Of course, this would have been long enough ago that people didn’t know what a coronavirus was, but humankind managed to recover anyway. These older coronaviruses now permeate among the population. People often become exposed at a young age, and, as with SARS-CoV-2, the vast majority of children have no symptoms or a minor respiratory infection. Even though immunity to these viruses diminishes over time, because they are endemic and continuously circulate through the population, every few years our immune systems are again exposed and receive a refresher course on how to kill the virus.
With possible exception to geographically isolated locations like Iceland and New Zealand, SARS-CoV-2 is on a path to becoming endemic like its older endemic coronavirus siblings. In fact, since March, for most regions containment has no longer been a strategy for managing SARS-CoV-2 as it was during the previous SARS and MERS outbreaks. SARS and MERS have a higher fatality rate than Covid-19, and it is for that very reason they were able to be contained. Since patients infected with SARS and MERS were more often symptomatic, generally developed more severe symptoms, and had a shorter period of time between exposure and the onset of symptoms, cases were recognized sooner, contacts were more easily traced, and further spread was prevented through quarantining.
While contract tracing and quarantining strategies remain important during the Covid-19 pandemic, they are aimed at protecting vulnerable groups and reducing the overall transmission of the virus rather than ultimately containing or eradicating the virus. At this point eliminating SARS-CoV-2 worldwide is essentially impossible. Fortunately, however, as was the case with the four endemic coronaviruses, eradication is not a requirement for the pandemic to end.
2. Because the novel coronavirus is so much more deadly and harmful than the other four endemic coronaviruses, won’t society have a huge problem if it becomes endemic?
Despite all the talk (and I’m not discounting that these are important things to discuss right now) about why SARS-CoV-2 is so infectious with its spike protein and ability to damage endothelial tissue, by far the biggest reason Covid-19 is so deadly is that before autumn of 2019 no human immune system in the world had ever encountered the virus. In contrast, the endemic coronaviruses don’t spread as quickly or with such lethality because most people’s immune systems have seen them before.
I’ve seen adults, children, and infants in the hospital infected with one of the four older coronaviruses. These patients almost always recover. I’ve cared for the hospitalized, frail, and elderly suffering from Covid-19 and, as you know, recovery is far from a guarantee.
However, I can all but guarantee that the vast majority of people who recover from Covid-19 now aren’t going to be dying from it in their later years — for the same reason we don’t see waves of elderly people succumbing to the endemic coronaviruses. On a repeat encounter with SARS-CoV-2, their immune systems will know what to do. Even if their immunity has waned and some develop symptoms, a re-exposure will generally result in a recovery rather then a fatality.
All this means that SARS-CoV-2 won’t always be as deadly as it is now. It is destined to become the fifth endemic coronavirus, and in all likelihood, over time it will become no more deadly than the common cold.
3. If herd immunity is the only foreseeable way the pandemic will end, don’t we need a vaccine in order for this to happen?
If you’ve been following the situation closely, you are likely familiar with the term, herd immunity, which can be defined as the minimum percentage of a population needed to be immune to a disease in order for the disease not to transmit efficiently. Estimates vary, but it is thought that somewhere around 45–60% of the population must develop immunity to Covid-19 either naturally or by vaccination in order to slow and eventually stop the spread of the virus.
Recall that humans in the past — populations that included our ancestors — managed to recover from coronavirus pandemics or epidemics. This didn’t occur because of a vaccine or medicine, it was on the strength of their collective immune systems. Did people have healthier immune systems back then? It’s possible. Did fewer people die because the population was younger? Also possible, but regardless, humans managed to develop herd immunity to these older coronaviruses without even trying. It just sort of happened.
Don’t get me wrong, as a doctor, I’m a huge supporter of vaccines. Measles and polio are fantastic examples of how vaccines can be a life-saving method of establishing herd immunity. But humans have also achieved herd immunity by natural means with other viruses such as parainfluenza, human metapneumovirus, and the four endemic coronaviruses. So, while I am grateful for the brilliant investigators all over the world diligently striving to develop a vaccine, I hope it has become apparent that, whether help arrives from a vaccine or not, we will indeed overcome this virus.