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A person who has been vaccinated against COVID-19 will have a slightly different immune response to the coronavirus than someone who was previously infected, researchers say. How long does immunity last—and is it all about antibodies?

How your immune system is primed may impact your long-term immunity.

A person who has been vaccinated against COVID-19 will have a slightly different immune response to the coronavirus than someone who was previously infected, researchers say. How long does immunity last—and is it all about antibodies?

How Long Does Covid-19 Immunity Last?

How your immune system is primed may impact your long-term immunity.

Body & Brain

How Long Does Covid-19 Immunity Last?Published: November 10, 2021Narrator: If you’ve been vaccinated against COVID-19, or if you’ve had a COVID infection, should you get a booster shot? How long are you still protected?It’s super complicated, but we do know that the immune system learns to fight COVID-19 through vaccination or in a less predictable way, from infection. And how your immune system is primed may have an impact on your long term immunityJohn Wherry: What happens during an infection is the virus comes in, in this case, in your nose and your upper respiratory tract and starts to replicate in the lining of your nasal passages and eventually the lining of your lungs. The virus causes damage when it does that, killing cells and actually inducing more and more inflammation.Narrator: So, vaccines give your immune system a leg up in the race against the virus.One of the early lines of defense your immune system deploys is antibodies. And in the case of vaccination or infection, your body makes a ton of them. These are tiny proteins that can lock onto parts of the virus. Most of the vaccines stimulate production of antibodies that will lock onto the spike protein that sticks out of the virusDeepta Bhattacharya: The virus needs that spike protein to attach to cells and to enter. And if you have antibodies that block that step, then it prevents viruses from getting in in the first place and then spreading if it happens to slip past that first wave of antibodies.Narrator: These are called “neutralizing antibodies because they can prevent the virus from entering your cells. Right after vaccination or infection, most people have lots of antibodies though in the early stages of your immune response, they might not be the best match against invadersBhattacharya: So basically if you happen to encounter a virus right in that early period, those antibodies, what they're doing is they're bouncing on and off the spike.Narrator: But antibodies evolve, even as they fight invaders. B cells create tons of variations of antibodies by scrambling their genetic code, and some of those are better at binding to the virus than others. And the B-cells that make the best antibodies are given the signal to make more, faster.Bhattacharya: There's a training process where the B cells that produce these antibodies are competing with each other to figure out who's the best. And it's only those cells that stick around and produce those antibodies.Narrator: Some research suggests that antibodies continue to evolve for several months. It's a good thing the antibodies get more efficient, because that initial spike in antibodies—that first wave—eventually starts to drop off.Theodora Hatziioannou: About two months post infection or vaccination, you have probably the highest levels of antibodies, and then they start declining. Then they reach a plateau. They do not decline significantly further. They just stay that.Bhattacharya: You basically don't take nearly as much of a hit as those antibodies are declining as you might expect, because the quality of those antibodies is improving.Narrator: Researchers don't yet know what levels of antibodies are protective against disease or infection, or if antibody levels are the best measure of immunity.They are however relatively easy to measure compared to other immune responses.Hatziioannou: We actually do not know what the precise effect of those waning antibodies in protection, the various categories of protection might be.Narrator: That decline in antibodies could have consequences if they wane too much in the presence of a lot of virus.But another line of defense—the memory arm of your immune system—may persist in your body for months, maybe even years.Bhattacharya: There are many layers of immunity beyond just antibodies. That cellular memory tends to be much more stable than the antibodies.So even if you do get an infection after you've been vaccinated or after you've recovered from an infection, you're not starting from the same point that you did the very first time you encountered a virus.Narrator: The T-cells, that kill infected cells and the B-cells that make new antibodies learn about the virus as they fight the virus—or in the case of the COVID vaccines—a piece of the virus. And after that threat is cleared, cells known as memory B- and T-cells, hold on to information about that invader and then lay in wait, ready to jump into action if there’s a new infection.Wherry: You now have this pre primed, or memory in your immune system so that you don't have to go through this whole process all over again. And you don't have to wait for your immune system to be educated.So what we're seeing in some of these infections and people who got vaccinated is they get maybe a little bit of mild symptom, but they don't get sick. They don't end up in the hospital. They don't end up with severe disease because the backup plan in the immune system is the memory cells, that jump into action much more quickly if you've been vaccinated.Narrator: There’s some evidence that suggests immunity after infection might be different than immunity after vaccination. And those that received the vaccine after recovering from an infection may actually have a stronger immune response than those who have never been infected.Wherry: So people are calling it super immunity, hybrid immunity. There are different terms for this. So you do seem to get some benefit of receiving the vaccine from an immunological standpoint. Your antibody levels are higher.That may protect you for longer because you've had essentially three exposures to the immune system being trained. You've had the infection in two doses of vaccine.Narrator: But allowing your immune system to prime by infection is really risky—the virus could do a lot of damage before your immune system catches up.In one of the only long term studies to look at three types of immune responses to COVID—antibodies, T-cell and B-cells, researchers followed two groups of vaccinated people for six months. One group had been infected with the virus and the other had not. And they found that vaccination helped long term cellular memory.Wherry: Memory-B and memory-T cells with some limits, they actually get better over time. And after a bit of rest, they actually become even more responsive.Narrator: Sounds like good news but a growing body of evidence suggests that vaccine’s protectiveness wanes somewhat in the first year after vaccination although vaccines are still very effective at preventing disease.Hatziioannou: They just observe that at six months you'll have an increase in symptomatic infections in the vaccinated population regardless of age.If that is the case, then the third shot is absolutely recommended because that's exactly what it's going to do, is going to boost your neutralizing antibodies further and potentially help stop this increase in symptomatic infections in vaccinated people.In my personal opinion, this is an experiment I don't want to do. Let's just stay ahead and include as many people as want to get the third dose. I think at the moment it is far more risky to wait and see what happensNarrator: Some experts argue against the need for booster shots—at least for most healthy vaccinated people—when much of the world remains unvaccinated.In addition to the continuing dangers of COVID for the unvaccinated, they point out that the more covid thrives, the more it will mutate—producing new variants that might be harder to fight.Bhattacharya: So the question is, if we start doling out these doses in this country and in Europe and in Canada because it will follow, does that impact our ability to get vaccines out to some of these lower income countries? And does that prolong the duration of the pandemic? And I think these are really complicated questions that they just haven't seen answered adequately.Immunologically speaking, those first two shots are so much more important than third ones.Narrator: Now boosters shots are authorized by the FDA and recommended by the cdc for certain high-risk groups, including those 65 and older.Hatziioannou: It appears that your your immune response is also overall wane with age.If you are at high risk of exposure due to work coming into contact with a lot of people, then also your chances of developing severe disease increase just because you are exposed to much higher viral load to just increase the probabilities. Why not protect those people regardless of age as much as we canNarrator: While there are still many unanswered questions, this may be the closest studied immune response to any virus in real time which gives some researchers a glimmer of hope—that our understanding of the immune system and how it battles viruses is getting better and better.

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Support Provided By

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Lingering Symptoms from COVID-19 are “Unprecedented”

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