Reviewed by Majed Koleilat, MD, Deaconess Clinic Allergy and Immunology
This is a very common question that we often receive, along with many other doctors and pharmacists, and we understand why people ask this question. When you’ve had an illness, why would you need a vaccination to prevent getting it again?
However, COVID-19 infection leading to “natural immunity,” and the risk of future infection, isn’t nearly as straightforward as many other illnesses.
According to a study in Kentucky earlier this summer1, 2
, unvaccinated people who have had COVID-19 are more than twice as likely to be re-infected than those who are vaccinated. Given the prevalence and increased transmissibility (contagiousness) of the Delta variant, this number is likely even higher now.
We’ll break down the reasons why those who have had COVID-19 in the past still need to be vaccinated, as well as why prior infection isn’t necessarily a helpful piece of information when it comes to current COVID-19 infections and hospitalization rates.
1) "Natural Immunity" wanes.
Natural immunity results from the antibodies made by a person’s immune system when they’re infected with a particular pathogen. When someone is infected with COVID-19, they do develop antibodies to the SARS-COV-2 virus (the virus that causes the COVID-19 infection). But over time, those antibodies begin to reduce in number. This process is different from person-to-person, and impossible to predict.
2) Natural immunity doesn’t adequately protect against variants.
Why Sharing Prior COVID-19 Infection Data Isn't Helpful
The genetic make-up of viruses changes and evolves over time. (For example, the flu changes each year, requiring a somewhat different shot every fall.) SARS-COV-2 is doing the same thing, and prior infection from earlier variants of the virus may not offer the same protection for new variants. Immunity from vaccination, however, offers broader coverage because it creates antibodies to the protein on the outside of the virus, which is remaining more consistent. That means a vaccinated immune system is more prepared to recognize variants of the SARS-COV-2 virus.
3) Natural immunity is not predictable.
Different people get exposed to different viral loads (quantities of viruses). In a studied vaccine, everyone gets the same dose. This makes the response predictable.
Let’s use chickenpox as an example. For those of us old enough to have been infected with chickenpox prior to vaccination availability (about age 25 or older now), we probably know someone who had chickenpox twice. In those cases, the first chickenpox infection was likely mild, which meant that their immune system didn’t create adequate antibodies to prevent a second infection.
That is now COVID-19 infections seem to be working. Mild-to-moderate SARS-COV-2 infections tend to not create as strong of an immune response to the virus, allowing reinfection.
Additionally, those who had severe cases of COVID-19 may not mount an adequate antibody response, due to timing (an infection many months ago), or unknown immune suppression (contributing to the severe infection in the first place). Those who have had severe infections are being re-infected, although at a lower rate than those with a milder infection.3
Vaccination, on the other hand, delivers a precise, equal and measurable dosage, which instructs the body to make antibodies that recognize multiple versions of the virus. This is predictable and easier to study.
4) Vaccination reduces the likelihood of both contracting or spreading COVID-19.
People who have had both a COVID-19 infection and are vaccinated are believed to have the best protection from future infection.
People with natural immunity but are unvaccinated may be more likely to spread infection to others because we cannot predict how protected they are (see #3, above) and now because of the highly-contagious Delta variant.
People who are vaccinated don’t have as high of a viral load as an unvaccinated person (amount of virus in their nose and throats) for as long of a time span4. That shorter time span can reduce the likelihood of spreading to others, especially at the beginning of the infection, when one may be asymptomatic or with minor symptoms.
Additionally, as more people become vaccinated, making their bodies an unhospitable host to the SARS-COV-2 virus, the more we can reduce the risk of future variants. Every time a virus replicates, there is the risk of a new variant forming.
5) Vaccination reduces current and future suffering.
One of the most difficult feelings for any human to process is regret. When unvaccinated people get seriously ill with COVID-19, or when people realize they’ve given COVID-19 to someone else, it leads to feelings of regret and “shoulda, woulda, coulda.”
Being unvaccinated increases the risk of severe illness, which can have long-lasting consequences for not only the patient, but their family who is counting on them. And as mentioned earlier, vaccination reduces the risk of giving COVID-19 to someone else…someone who may not do as well. No one wants to learn that a loved one, or a patient you were caring for, passed away because of a COVID-19 infection that you gave them.
In healthcare, when sharing information about COVID-19 infections and hospitalizations, we’re often asked why we don’t include the numbers of people who have had COVID-19 before. Including that data isn’t helpful in drawing meaningful conclusions because of many variables explained above, including:
- When did someone have COVID-19?
- How severe was it?
- Which variant/strain was it?
- What percentage of the overall community has had COVID-19, to recognize if it’s a proportional number?
So listing a “yes or no” for prior COVID-19 infection isn’t always a meaningful statistic, compared to whether someone has been vaccinated. Prior infection is not always a useful predictor. Listing vaccination is far more straightforward and precise, as we know how many eligible people have been vaccinated, what their dosage was, etc.
The greatest variable now among listing vaccination numbers is those who are immunocompromised (due to medical conditions or age) resulting in their body’s inability to mount as strong of an immune response to the vaccine. That factor is why 3rd doses are being recommended for that group of patients. More information on third dose eligibility
You can schedule a vaccine at Deaconess at www.deaconess.com/vaccines,
or at area pharmacies and other locations at www.vaccines.gov.
Dr. Koleilat is board certified in allergy and immunology, and pediatrics. He completed his fellowship in Allergy and Immunology at Duke University, and is a member of the American Academy of Asthma, Allergy and Immunology.