COVID-19 Vaccine: Immunity Questions and Answers: Shot

When the COVID-19 vaccine is deployed, three major questions arise. First, can vaccinated people still spread the disease? Second, does the vaccine remain effective as the virus evolves? And third, how long will vaccine protection last?

The answer to these questions lies in our immune system. And the answer is not easy because our immune system is very proficient and very difficult to predict.

Let’s start with the first question. It’s about whether vaccinated people can still spread the disease. Marion PepperImmunologists at the University of Washington say this is an open question about the vaccine in general, not just this vaccine.

“We’re constantly attacked by a variety of pathogens, and I don’t know when your immune system is responding, so I think it’s hard to say,” she says. We never know about them, as there may be infections that do not get sick. However, we may be spreading the disease.

When a person becomes infected or vaccinated, the immune system prepares to produce antibodies that specifically target the virus. Over time, these antibodies naturally declined. However, the immune system still retains the memory of the virus, and when the virus reappears, the cells begin to move and prepare new batches of antibodies. However, the process can take 3-5 days.

During that time, the virus can start replicating in the body.

“It’s a bit of a race between the immune system and the virus.” Dr. Michel Nussenzweig says, Researcher at Howard Hughes Medical Institute, Rockefeller University.

When the immune response begins immediately, few viruses are produced. Your ability to spread the disease is “actually a function of the amount of virus you are producing,” says Nussenzweig.

It seems that the human immune system is likely to win the arms race, but scientists do not yet have the data to say it with confidence. Therefore, vaccinated people are required to wear a mask and take other precautions until it is resolved.

Another wildcard here is that the lungs and nasal passages contain so-called T cell populations. These cells are prepared to identify cells infected with the virus. This type of T cell remains in the tissue and is much more difficult to study. As a result, scientists studying blood samples will not see them.

Because these T cells are prepared to react immediately, they can also help bridge the gap between the time of infection and the time the immune system can initiate a complete response with antibodies.

“In influenza, T cells embedded in tissues can have the dramatic effect of limiting infection,” he said. Stephen Jameson, Immunologist, University of Minnesota School of Medicine. But “we still don’t know enough,” he says, whether they work for COVID-19 as well.

The second question as to whether the vaccine remains effective as the virus evolves is difficult to answer. So far, scientists are less worried about the current strain of the virus that is widespread around the world. Vaccines clearly seem to work against them. However, the virus continues to transform and the results are uncertain.

“Everyone is clearly worried about the evolution of the virus, but the responsiveness of memory B cells also evolves over time,” says Pepper.

Memory B cells are an important component of the immune system because they remember infections. They are lurking in the bone marrow and are ready to turn into antibody-producing cells when the “remember” virus reappears in the body.

But they don’t just remember the specific antibodies that acted against the virus in the past. It is also possible to randomly generate similar new antibodies. This may be more effective against virus strains that the body has never seen before.

“Mature cells deliberately introduce mutations into DNA at almost the only time in the body,” says Pepper.

However, while this system is noteworthy, it has its limitations. Viruses that change significantly from one year to the next, such as the flu, can defeat this system. Therefore, a new flu shot is required every year. The coronavirus that causes COVID-19 mutates much more slowly than influenza, but it is not yet clear whether memory B cells are sufficiently adaptive to suppress the virus permanently.

Finally, the question is how long the vaccine will last.

In some cases, the memory of the immune system can be very long.

“Some natural infections can give you lifelong immunity,” says Jameson. “You get it only once and you are protected for the rest of your life.”

Vaccines mimic natural infections and provoke an immune response. However, vaccines may require a boost to keep their immunity strong. Memory B cells that target the coronavirus that causes COVID-19, for example, may not have the sustainability of the cells that protect us from measles. So far, scientists have observed that these memory B cells persist for months after a case of COVID-19, but to say nothing about whether they will eventually decline. Is premature.

“The good thing is that if it turns out, there will be an opportunity for some decline in the immune response,” says Jameson. “Then, like many other vaccines, maybe … you’ll get another booster after a year or something.”

These questions reflect how scientists have come to understand our immune system in recent years. COVID-19 also reveals that we do not yet know how the immune system protects us from infectious bacteria.

“It’s very interesting to see this unfold in real time, because we’re learning a lot about the virus and its immune response in ways never before,” says Pepper.

You can contact Richard Harris, correspondent for NPR Science [email protected]..