As the United States rounds out its second year of the pandemic, many people are trying to figure out just how vulnerable they may be to COVID-19 infection, and whether it’s finally safe to fully return to all the activities they miss.
On an individual basis, the degree and durability of the immunity a person gets after vaccination versus an infection is not an easy question to answer. But it’s one that science is hotly pursing.
“This virus is teaching us a lot about immunology,” says Gregory Poland, MD, who studies how the body responds to vaccines at the Mayo Clinic in Rochester, Minn. Dr. Poland says this moment in science reminds him of a quote attributed to Ralph Waldo Emerson: “We learn about geology the morning after the earthquake.”
“And that’s the case here. It is and will continue to teach us a lot of immunology,” he says.
It’s vital to understand how a COVID-19 infection reshapes the body’s immune defenses so that researchers can tailor vaccines and therapies to do the same or better.
“Because, of course, it’s much more risky to get infected with the actual virus, than with the vaccine,” says Daniela Weiskopf, PhD, a researcher at the La Jolla Institute for Immunology in California.
What is known so far is that how much protection you get and how long you may have it depends on several factors. Those include your age, whether you’ve had COVID-19 before and how severe your symptoms were, your vaccination status, and how long it has been since you were infected or inoculated. Your underlying health matters, too. Immune protection also depends on the virus and how much it is changing as it evolves to evade all our hard-won defenses.
In a new scientific brief, Here’s what we know so far:
Durability of immunity
The agency’s researchers say if you’ve recovered from a COVID-19 infection or are fully vaccinated, you’re probably in good shape for at least 6 months. That’s why this is the recommended interval for people to consider getting a booster dose.
Even though the protection you get after infection and vaccination is generally strong, it’s not perfect.
Getting COVID-19 after you’ve been vaccinated or recovered is still possible. But having some immunity -- whether from infection or vaccination -- really drops the odds of this happening to you. And if you do happen to catch COVID, if your immune system has already gotten a heads up about the virus, your infection is much less likely to be one that lands you in the hospital or morgue.
According to CDC data, at the height of the Delta surge in August, fully vaccinated people were six times less likely to get a COVID-19 infection compared with unvaccinated people, and 11 times less likely to die if they did get it.
How strong is immunity after a COVID-19 Infection?
About 90% of people develop some number of protective antibodies after a COVID-19 infection, according to the CDC. But how high those levels climb appears to be all over the map. Studies show peak antibody concentrations can vary as much as 200-fold, or 2,000%.
Where you fall within that very large range will depend on your age and how sick you became from your COVID-19 infection. It also depends on whether you have an underlying health condition or take a medication that blunts immune function.
Our immune system slows down with age. Immunosenescence starts to affect a person’s health around the age of 60. But there’s no bright line for failure. People who exercise and are generally healthy will have better immune function than someone who doesn’t, no matter their age. In general, though, the older you are, the less likely you are to get a robust immune response after an infection or a vaccination. That’s why this group has been prioritized both for first vaccine doses and boosters.
Beyond age, your protection from future infection seems to depend on how ill you were with the first. Several studies have shown that blood levels of antibodies rise faster and reach a higher peak in people with more severe infections.
In general, people with cold-like symptoms who tested positive but recovered at home are better protected than people who didn’t get any symptoms. And people who were hospitalized for their infections are better protected over the long term than people with milder infections. They may have paid a steep price for that protection: Many hospitalized patients continue to have debilitating symptoms that last for months after they go home.
On average, though, protection after infection seems to be comparable to vaccination, at least for a while. Six large studies from different countries have looked into this question, and five of them have used the very sensitive real-time polymerase chain reaction test (RT-PCR) to count people as truly being previously infected. These studies found that for 6 to 9 months after recovery, a person was 80% to 93% less likely to get COVID-19 again.
There are some caveats to mention, though. Early in the pandemic when supplies were scarce, it was hard to get tested unless you were so sick you landed in the hospital. Studies have shown that the concentration of antibodies a person makes after an infection seems to depend on how sick they got in the first place.
People who had milder infections, or who didn’t have any symptoms at all, may not develop as much protection as those who have more severe symptoms. So these studies may reflect the immunity developed by people who were pretty ill during their first infections.
One study of 25,000 health care workers, who were all tested every 2 weeks -- whether they had symptoms or not -- may offer a clearer picture. In this study, health care workers who’d previously tested positive for COVID-19 were 84% less likely to test positive for the virus again. They were 93% less likely to get an infection that made them sick, and 52% less likely to get an infection without symptoms, for at least 6 months after they recovered.