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How Does Having COVID Affect Your Immunity?

Medically reviewed by Susan Kerrigan, MD and Marianne Madsen on February 22, 2022

There’s a good chance you’ve had COVID-19. Last September, as the virus’s Delta variant was cresting, the U.S. Centers for Disease Control and Prevention estimated that an astounding 146 million Americans had already been infected. During the Omicron wave which followed, the record-breaking number of people testing positive for the virus reached over 800,000 in a single day.  Even more startling, some estimates are that 80-90 % of Omicron infections are completely asymptomatic –– twice as many as with Delta. Which means untold millions of infected people felt completely healthy over the holidays –– and most of them didn’t get tested. 


So let’s assume you’ve already had COVID. How will your immune system handle the next wave?  Recently researchers tested unvaccinated volunteers to see how prior infections affect immunity. Here are the surprising results and what they suggest for society’s rapid reopening.


Growing Familiarity 


Two years ago, the coronavirus was truly novel. Researchers were unsure of how it was transmitted and how it would affect the population. By the time it reached U.S. shores, it had already infected thousands in China and Europe. Generally, older patients fared the worst. Today, the CDC reports more than 81% of COVID-19 deaths occur in people over age 65 with their overall fatalities from the virus nearly 100 times than of adults under the age of 30. Other risk factors include being immunocompromised, having cancer or being overweight. In fact, the agency suggests that, “People who do little or no physical activity, or exercise, are more likely to get very sick from COVID-19 than those who are physically active.” Upsetting news for anyone whose favorite fitness center, swimming pool, or yoga studio was closed or even went out of business due to lockdowns and restrictions –– especially considering that in 2020 data analytics platform Evidation estimated that physical activity levels had plunged nearly 50% compared to 2019.


Yet long before the vaccines, most people who were exposed to COVID-19 were relatively unaffected. Children, for the most part, enjoyed a naturally powerful immune response which not only prevented illness but also prevented symptoms. Others remained healthy despite being close to family members who became seriously sick or even died. The human immune system is a complex machine and, even when confronted with an unknown virus, most people are capable of mounting a robust response. 


While seven out of ten Americans are now fully vaccinated (with a far smaller percentage “boosted”), a consistent cluster has refused the shot. Many are young and thus presumably at low risk; others are rural or White. Most media outlets along with some medical journals and even government health agencies have consistently reported that the unvaccinated are the most likely to die or be hospitalized. A decent percentage of the vaccinated public has even blamed them for the start-stop of societal reopening. Still, as we pass the two-year mark of the pandemic, it’s also important to distinguish between someone being hospitalized because of COVID-19 versus someone entering a hospital with COVID-19. In other words, if you sustain injuries in a car crash and test positive as part of normal hospital procedures, you could be included in the number of people hospitalized with the virus. This was less of a concern in the early days of the virus, both because (1) testing was less widespread and (2) most patients with the virus were being admitted with serious COVID-related illnesses. 


Now, however, statisticians are working to determine who has been hospitalized with the disease. They are also breaking down hospital admissions between vaccinated and unvaccinated. During a five-month examination of vaccine effectiveness (VE) against COVID-19–associated emergency department/urgent care (ED/UC), the Centers for Disease Control and Prevention recently published some surprising information. Looking at a period when Delta or Omicron were the primary variants, among nearly a quarter of a million “ED/UC encounters…Among persons with COVID-19–like illness seeking care at ED/UC facilities, 46% were unvaccinated, 44% had received two doses of vaccine, and 10% had received 3 doses.” In other words, most people entering medical facilities with the virus during the time in question had gotten at least one shot. So what’s better for long-term immunity –– prior infection or a shot in the arm?


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COVID-19 - Positive Test

COVID-19 - Positive Test

Shifting Data


“Infection-conferred protection” isn’t just a benign medical term. It’s become heavily politicized. Before most national vaccine mandates were halted by various federal courts, they generally made no provision for prior immunity. Many in the media reported that it was insufficient protection, despite a preponderance of evidence suggesting otherwise. Numerous smaller studies echoed the findings of a massive Israeli study that found natural immunity was 27 times more effective than vaccinated immunity at preventing COVID symptoms. 


When Novak Djokovic anonymously submitted his prior infection as evidence that he shouldn’t be required to be vaccinated in order to play in the Australian Open, it was accepted by the country’s medical board. However, when he arrived, his fame was a driving factor in the revocation of his visa because, as the person who sent the tennis star packing, Australian Immigration Minister Alex Hawke explained, allowing Djokovic to play “may be counterproductive to efforts at vaccination by others in Australia.” Djokovic has no plans to get the shot and believes his December bout with the virus offers sufficient immunity. Is he right?


In a recent study, unvaccinated adults were asked to participate in an examination of their antibodies. Some 750 took part. Slightly more than half were female and over 80% were White. The mean age was 48 and just 14 percent admitted to wearing masks in public. They fell into one of three groups: (1) Those who had tested positive for COVID-19, (2) those who suspected they’d had it but hadn’t gotten a test, and (3) those who believed they’d never had the virus. 


With an average of almost nine months since infection, some 97% of those who had had the virus tested positive for anti-RBD antibodies. These antibodies occur because of a person’s immune response following contact with SARS-CoV-2 (which causes COVID-19.) They are effective at preventing symptomatic or serious infections the second time someone encounters COVID-19. This antibody response is the driving benefit of vaccines. Yet, in some cases, even after a booster, the shot’s antibody protection was just 37% effective at preventing hospitalization five months later according to the CDC. 


During the study, it wasn’t just those with confirmed prior infections who had antibodies. Over half of those who suspected they’d been infected had anti-RBD antibodies along with 11% of those who’d been convinced they’d avoided contracting the virus. Although many displayed the antibody response, a relatively low number exceeded the 1000 U/mL routinely exceeded by those who got the mRNA vaccine. Still, vaccine-conferred immunity appears to wane over time while the study discovered ongoing immunity in unvaccinated healthy adults 20 months after confirmed COVID-19 infections. Further, antibodies aren’t the only protection. The reason many children (and adults) remain asymptomatic or never even get the virus is because of T-cell response –– which often does the heavy lifting of the immune system. 


With prior infections and vaccinations coupled with the Omicron’s variant’s rapid spread, we may actually be approaching the ever-elusive herd immunity. While future virulent variants are certainly possible, over time, successful viruses tend to become less deadly. Individuals and families should make their own risk assessments, and those who are at higher risk should continue to exercise caution. Still, we may be close to something even better than “normal.” After all, the Roaring Twenties followed the world’s last major viral pandemic at a time when medicine was far less advanced.


Written by John Bankston



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