Antibodies are proteins made by the immune system in response to an infection or vaccination. They are present on the surface of important cells of your immune system called B cells. Other immune cells called T cells help clear the infection.
Antibody tests can detect the body’s levels of antibodies against a certain virus. When a test detects antibodies, it means that a person was previously infected or vaccinated for a disease such as COVID-19. Thus, antibodies are a signal that an individual is likely protected from future infection.
This article will explain what antibodies are, how they work, and how they differ when acquired from infection or vaccination.
How Antibodies Defeat Infections
Antibodies play a key role in fighting certain types of infections. They work with other parts of your immune system to get rid of pathogens (bacteria or viruses that cause disease). That includes SARS-CoV-2, the virus that causes COVID-19.
However, it takes a while for this to work. If your immune system has never dealt with a particular virus before, it won’t have antibodies to the virus ready to go.
Neutralizing Antibodies
Antibodies attach very precisely to a specific spot on a given virus. So it takes your immune system a while to figure out which exact antibody will work to neutralize (counteract) a virus.
That’s one of the reasons it takes you a while to get better after you are infected with a new virus. Depending on the specific type of antibody, it can take a couple of weeks or so to produce the right antibodies in large enough amounts.
Antibody Types
The body usually first produces a specific antibody type called IgM. Sometimes, doctors will test for IgM antibodies to see if you have recently been infected with a certain virus. For example, doctors commonly use this kind of test to check for recent infection with the hepatitis B virus.
Neutralizing vs. Non-Neutralizing
Even though antibodies are important for fighting and preventing many infections, not all antibodies the body produces against a virus are effective.
A little later, the body produces other types of antibodies. An essential type is IgG antibodies. These tend to last longer than IgM antibodies.
How Antibodies Prevent Infections
After an infection, certain T cells and B cells that can recognize the virus stick around for a long time. Then, when they are re-exposed to the virus (or another pathogen), these special memory cells recognize it quickly and respond.
IgG antibodies are critical for controlling the initial disease and preventing re-infection if you are exposed again in the future.
Recap
Antibodies trigger your immune system to fight infection. They connect to a specific spot on a virus to inactivate it.
When this happens, you don’t get sick. Or, if you do get sick, you usually only get a very mild version of an illness.
This is called protective immunity to a disease. Depending on the situation, this immunity might last for months or years.
You might also have partial immunity. This is like giving the immune system a head start that offers you some degree of protection, but not total protection.
COVID-19 Antibodies
Antibodies have a key role in treating infection and preventing disease. That’s why scientists have been so interested in understanding the role of antibodies in COVID-19.
Plasma
The Food and Drug Administration (FDA) has granted Emergency Use Authorization (EUA) for some COVID-19 treatments. Some of the treatments include the use of plasma (the clear, liquid portion of blood) donated from people who have recovered from the illness.
While researchers initially hoped plasma containing antibodies to the virus might help individuals recover more quickly from an infection, recent research has not suggested plasma is effective in treating COVID. While some trials continue, the World Health Organization does not currently recommend it.
Synthetic Antibodies
Researchers have developed synthetic (chemical) antibody therapies that might end up being an important part of treatment. Several monoclonal antibody products received EUA by the FDA, but most of these EUAs were later revoked. Some of these antibodies are intended for prevention after exposure and early treatment in people who are high-risk for severe disease.
Vaccines
Studying how antibodies work in COVID-19 has also been critical for developing successful vaccines. This knowledge is also important for assessing how immunity to COVID-19—either from infection or a vaccine—decreases over time. This will help scientists determine when people need booster vaccine shots to re-up their immunity.
Antibodies From Natural Infection
When you develop antibodies through illness, your immune system reacts to protect you. First, it goes through a process of identifying the virus and eventually making effective antibodies.
Your B cells make antibodies to different parts of the virus. Some of the antibodies your body makes are effective, and some are not. These help you eliminate the virus and recover. Hopefully, some of these antibodies also help protect you from future infections.
For example, infection with COVID-19 seems to give you some protection from being re-infected, at least in the short term. A study published in March 2022 compared unvaccinated people who had and had not been previously infected with COVID-19. Those previously infected were 86% less likely to be reinfected. However, protection waned more than one year after infection. The authors note that this study was conducted prior to the development of the more contagious delta and omicron variants, meaning these results may no longer be applicable to protection against these newer COVID-19 strains.
However, other studies have found much shorter durations of protection—some as short as three months. Researchers believe the variation may be a result of a combination of factors, including individual susceptibility as well as exposure levels.
Studies have indicated that people with symptoms of COVID-19 also seem to produce effective “neutralizing” antibodies. In fact, contracting COVID and then getting vaccinated appears to produce the most robust protection against later reinfection. In the March 2022 study mentioned above, which looked at more than 35,000 people, the authors found that “infection-acquired immunity waned after 1 year in unvaccinated participants but remained consistently higher than 90% in those who were subsequently vaccinated, even in persons infected more than 18 months previously.”
In a 2022 study, researchers concluded that reinfection after natural infection is seven times more likely than infection after vaccination. However, these data were compiled before the advent of the delta and omicron variants. Since these variants are more contagious, this reinfection rate may now be higher.
How Long Might Natural Immunity Last?
How long protective immunity lasts after infection varies for different types of viruses.
Some viruses mutate (change) rather quickly. That means when you are exposed to a new strain of the virus, your previous antibodies might not work. This is why a new flu vaccine is created each year.
Immunity to some types of coronavirus may be short-lived. For example, people can get cold-like symptoms from certain coronaviruses season after season.
But coronaviruses don’t mutate as rapidly as viruses like the flu. This may mean that protective immunity could last longer for COVID-19 than it does for something like the flu.
Antibodies to COVID-19 do appear to decrease in the months after infection. However, that happens for all infectious diseases. Therefore, it doesn’t necessarily mean that immune protection is decreasing.
B cells may decrease their antibody production in the months after infection. But memory B cells can continue to circulate in the bloodstream for years. Presumably, these B cells could start releasing the neutralizing antibody if they were again exposed to the virus.
After they have studied a virus for a long time, scientists can determine whether a person is immune based on a blood test. For example, they might look for a certain concentration of a specific antibody.
Since people’s immune systems respond very differently to natural infection, it is difficult for scientists to pinpoint how long natural immunity to COVID-19 might last for a specific individual.
The COVID-19 vaccine is recommended even for people who have recovered from the virus because people’s immune systems respond more consistently to vaccination than to a prior infection.
However, researchers have been gathering data on what immunity looks like. In one study published early in the pandemic, researchers found antibodies in the majority of people three months after experiencing symptoms from COVID-19.
Another study published in November 2021 looked at antibody response to the Pfizer vaccine over a longer period of time. After a second dose of the vaccine, antibody responses declined at three months, and declined further after six months, the researchers found. At six months after the second dose, antibody response was similar to people recovering from COVID and to levels after the first dose. They also found elderly people had less antibody response.
In addition, experiencing more side effects from the vaccine correlated with stronger protection. How long immunity lasts might also be impacted by whether a person had an asymptomatic, mild, or severe infection.
Antibodies From Vaccination
Vaccination is a way for your body to build protective immunity without having to get sick first. Different types of vaccines do this in different ways.
Naturally acquired immunity happens after becoming infected with a particular illness. This usually protects from reinfection, at least in the short term. How long natural immunity lasts depends on the virus and how quickly it mutates.
Regardless of how a vaccine introduces your body to a virus, all vaccines essentially do the same thing:
- They expose the immune system to one or more proteins from the virus (or another pathogen).That exposure instructs your immune system to make B cells.Those B cells then make specific antibodies that can fight off a specific virus.
The vaccination process prompts the body to make memory B cells, just like they do in natural infection. If you are ever exposed to the virus again, these B cells go into action right away and release antibodies that can target the virus.
These antibodies stop the virus before you get sick. Or, in some cases, you might get sick but with a much milder case.
Vaccine vs. Natural Immunity
There are a lot of similarities but also sometimes some differences between vaccine immunity and natural immunity. For example, in response to an infection or vaccination with a live virus, IgM antibodies usually are made first, followed by IgG and some other types of antibodies.
That’s because your immune system already has a head start—one it wouldn’t have had if you hadn’t been vaccinated.
And just like in a natural infection, protective immunity doesn’t begin the moment you get vaccinated. It takes a couple of weeks or so for your immune system to form the antibodies and groups of B cells that it needs. That’s why you don’t get full protective coverage from a vaccination right away.
For the most part, the antibodies that you form from getting vaccinated are the same kind of antibodies you would get from a natural infection. One difference is that certain types of vaccines only show the immune system part of the relevant virus. Because of that, the immune system doesn’t form as many different types of antibodies as it would in the course of a natural infection.
However, this doesn’t mean that the antibodies formed are less effective than those formed in a natural infection. It’s just that someone who has been naturally infected might also have additional antibodies (many of which might be ineffective).
To make a vaccine, researchers carefully select a specific part of the virus shown in lab studies to trigger an antibody response that effectively neutralizes the virus.
Sometimes researchers can use this understanding to help make diagnostic decisions. For example, with hepatitis B, differences in certain antibodies can sometimes be used to determine if a person has an acute or chronic infection.
Protective immunity that builds over time
Body may be introduced to one specific antibody that has been found effective in fighting the virus
The specific antibody acquired through vaccination is effective at fighting the virus
Vaccines provide immunity without the risk of complications from exposure to a virus
Protective immunity that builds over time
Body may form many different antibodies in response to anillness
Some of the specific antibodies acquired through infection are effective at fighting the virus
Natural immunity comes with the risk of complications from exposure to a virus
It can also tell if they have been successfully vaccinated. People who got the antibodies through natural hep B infection have a specific antibody not found in vaccinated people (one not important for developing immunity).
Most of the vaccines for COVID-19 only show the immune system part of the virus. This is a protein chosen to trigger a strong immune response. (This includes the Pfizer, Moderna, and Novavax vaccines.) So, someone who had naturally been infected with the virus might have some additional antibody types not found in someone who had been successfully vaccinated.
The difference between vaccine-acquired and naturally acquired immunity is a very complex topic. You can’t just compare natural infection to vaccination because not every vaccine has the same properties. In addition, not every vaccine will trigger the same immune response.
COVID-19 Vaccines: Stay up to date on which vaccines are available, who can get them, and how safe they are.
In some cases, a specific vaccine might not provide as effective an antibody response as being naturally infected. But other times, the reverse might be the case. This is especially true if a vaccine has been designed to provoke a strong response.
We can’t make assumptions without studying the specific data over the long term.
Potential Risks of Antibodies
Antibodies provide many benefits. They eliminate infections and provide protective immunity against future infections.
Vaccines introduce your body to proteins from a virus. This prompts your body to make B cells, which produce antibodies to fight the virus if you become exposed. As a result, vaccination helps you avoid getting sick or getting severely ill.
However, in rare circumstances, antibodies might actually worsen an infection. For example, antibodies might bind to a virus in such a way that makes it easier to enter cells.
This might mean that if a person is re-infected after an initial mild infection, they could then have a more severe case the second time. Or, it theoretically might mean that a person could have a worse response to potential infection if they have previously been vaccinated for the disease.
This scenario has been called “antibody-dependent enhancement.” It has been found in viruses such as dengue. In that virus, it complicated the creation of successful vaccines.
Researchers are continuing to study how immunity and the antibody response change over time, as the virus changes and updated vaccines have been introduced. This will help determine when booster vaccines are necessary.
Because researchers were aware of this theoretical possibility, they have been looking very carefully to see whether this might be possible in COVID-19.
“Breakthrough” cases—infection after vaccination—have also become more common with new variants of the virus that causes COVID-19. While these cases occurred in only a small percentage of vaccinated people when the vaccines were first introduced, the protection the original vaccines provided against the omicron variants began to decline. Boosters have helped to restore some of that protection. One study from July 2022 found the two mRNA boosters (Pfizer and Moderna) offered significantly higher protection against omicron infection compared to protection from previous infection only.
Summary
Antibodies help your body fight off certain infections. They work when your body is actively ill. They also stick around to help prevent you from becoming re-infected.
Vaccines are another way your body can acquire antibodies. Vaccines introduce your body to one or more proteins from a virus. This prompts it to make B cells, which produce antibodies against a specific virus.
Vaccines are a safe and effective way to protect yourself from infectious diseases. COVID-19 vaccines are the safest way to protect yourself from COVID-19. They are widely available to everyone 6 months and older.
