Feature Article: COVID-19 — Natural Versus Vaccine-induced Immunity

The recommendation to get the COVID-19 vaccine even if someone was previously infected has been a point of contention for some who repeatedly ask, or at least wonder, why they need a COVID-19 vaccine if they have already been infected. Recently, immunity garnered from infection, so-called natural immunity, has been cited as an argument against mandates. So, we thought it would be a good time to discuss the nuances and considerations surrounding this topic.

Relying on our immune systems: Natural immunity

Our immune systems are awesome. They protect us from numerous attacks daily from the moment we are born until the moment we die. In most cases we remain unaware of this protective activity, but sometimes these outside challenges get the better of our immune systems. These may be minor, taking the form of a cold or even symptoms severe enough to spend a few days in bed. However, on rare occasions, we become more severely ill, going to the doctor or the hospital for medical care. Even more rarely, these infections may overwhelm an individual causing death.  

We are right to rely on the effectiveness of our immune systems, but we also need to be aware that not all assaults are created equal. Said another way, sometimes our immune systems have a better chance of success than others. So, what affects these chances?

• Strength of our immune system — We often talk about the importance of taking care of ourselves by doing things like eating right, staying active, and getting enough sleep. Though these things help, we would be foolish to think that our actions alone affect the calculation of risk when it comes to infectious diseases.
• Characteristics of the pathogen — Simply put, some pathogens are more dangerous to people than others. Before it was eliminated from the face of the earth, smallpox killed about 3 of every 10 infected people. Likewise, about 1 or 2 of every 10 people with invasive meningococcal disease die and another 2 of 10 live with resulting complications, such as deafness, nerve damage, or loss of limbs. And rabies, the most virulent of all infectious diseases, kills 100% of those with symptoms. In some cases, like the cause of COVID-19, pathogens are not uniformly dangerous in that certain subgroups of people are at greater risk, but the reality is that any organism that can cause disease can also cause death.
• Dose and timing — If a person is exposed to a large dose of pathogen or if they are exposed at a time when they are personally more susceptible, their immune system may also be at a disadvantage. These are factors that we often cannot control and may not even be aware of.

Not only do these factors affect the success of the immune system in terms of preventing infection or symptoms, they also affect our resulting immunity. As such, the strength and durability of immunity after infection can vary by individual. Further, while the severity of symptoms or illness often correlates with the strength of the resulting immunity, it doesn’t always. Said another way, we cannot assume that two previously infected individuals are equally protected, nor is it always the case that the one who had more severe illness will be better protected against future infection. 

Helping our immune systems: Vaccine-induced immunity

Another factor that affects the chance for immune system success is pre-existing immunity. Once our immune system has been introduced to a particular pathogen, it is better equipped to respond during subsequent exposures. So, indeed, previous infection better positions our immune system against future exposure, but because of those uncontrollable factors described above (e.g., characteristics of the pathogen, timing and dose), sometimes individuals pay a high price for natural immunity and individual levels of protection may be variable, leaving some more susceptible than others.

Vaccines, on the other hand, afford us control without taking the chance of experiencing severe illness or death. And, while vaccines are not 100% effective, they tend to provide more consistent immunity, and in some cases, such as with COVID-19 vaccines, a broader immunity that better protects against variants.

Sorting out how this relates to COVID-19

In the current situation related to COVID-19, some feel like the risks presented by natural infection are low and the risks presented by vaccination are high. Although the vaccines have been shown to be extremely safe, some may calculate and prefer the risk related to infection. Indeed, for many of them, that calculation will work out. They will get infected with COVID-19, have a mild or asymptomatic case, and gain immunity. But two important considerations related to this choice are warranted:

1. We cannot predict who among us will be severely affected because choosing to gain immunity through natural infection means relying on things that are out of our control (e.g., characteristics of the pathogen, dose and timing). And, while we know that certain subgroups of people are likely to be more severely affected by COVID-19, the reality is many “high-risk” people have weathered COVID-19 infections and many people with no underlying conditions have not.
2. And as mentioned, the immunity that follows natural infection can be variable. As such, some people will enjoy robust immunity after infection, while others may remain susceptible to reinfection, again needing to “win” the game of chance that comes with natural infection.

While vaccines do not work for everyone either, they more consistently position people with robust immunity and the price paid is significantly lower for the majority of individuals. And, while it is true that a few individuals suffer more severe side effects following vaccination, the risks of vaccination are minimal compared with natural infection. The severe side effects found following COVID-19 vaccination are rare and because they most often affect different subgroups of people, as shown on this infographic, individuals can choose a version that further decreases their individual risk.

SARS-CoV-2, the virus that causes COVID-19, is not going anywhere, so everyone will eventually gain immunity to it. Their immunity will come either from natural infection or vaccination. A recent study found that in May 2021, about 1 in 5 people had immunity to COVID-19 resulting from infection and about 3 in 5 had immunity from vaccination for a total populational immunity of about 83%. During that same period, about 594,000 people died from COVID-19 and as of November 2021 (see “What are the side effects of the COVID-19 vaccine?”), 5 people have died following COVID-19 vaccination (1 died from Guillain-Barré syndrome (GBS) and 4 from the blood clotting condition called thrombosis with thrombocytopenia syndrome or TTS).

Hopefully, this information helps demonstrate that vaccines provide us with an opportunity to control how we gain immunity in a way that natural infection does not.

A word about mandates

While mandates are often viewed as disregarding individual rights, they are really about community safety. Vaccine mandates increase our collective safety in the same way that traffic laws do. For everyone to be safer on the roads, we all need to give up a bit of our “individual freedom” to drive the way we want. Of course, if we could trust that everyone would drive responsibly, we would not need those traffic laws. But human nature does not always include thinking about the effects of our decisions on others. As such, all groups, including civilized societies, must have rules of behavior.

Considering this idea in relation to vaccines, if everyone who could get vaccinated would do so, mandates would not be necessary. But we know that even after considering the above information, some people will still decide that they want to take their chances with natural infection. However, like driving in traffic, that choice does not only affect them. It also affects everyone they come into contact with when they eventually get infected (or re-infected). As previously stated, the risk they decide to take is likely to work out for them and they won’t get very sick. But as the virus reproduces in the war with their immune system, others are likely to be exposed to the resultant viral particles, so the individual’s risk is extended to others by no choice of their own. As such, mandates end up being put into place to improve community safety.

So, people can keep talking about natural immunity, mandates and their individual rights, but the fact of the matter is we are all in this together, and we will only see our way out of it through high enough levels of community immunity. The difference will be the collective price we pay getting there.

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Last updated: Dec. 6, 2021