Why do we develop permanent immunity with some diseases and not with others? (And what will happen to the coronavirus)

¿Por qué con algunas enfermedades desarrollamos inmunidad permanente y con otras no? (Y qué sucederá con el coronavirus)

Against some diseases, there are vaccines that immunize us for life, but others, such as flu or seasonal influenza, require a new version every year. We asked two immunologists why

Once we become infected with certain diseases, such as measles, or get vaccinated against them once, we develop lifelong immunity. On the other hand, there are others, such as the flu, that require a new version of the vaccine every year.

The question now is what will happen to SARS-CoV-2: ¿a permanent immunity to the COVID-19, the disease-causing the new coronavirus?

To find the answer, we must observe what happens inside our body.

Here’s what two immunologists – one in the United States, one in Europe – say about the issue and why the vaccine is key to achieving immunity.

Your cells have memory

“When we talk about immunity, we mean being able to generate an immune response that protects us. And that response may or may not be lasting, “he tells BBC Mundo. Sheena Cruickshank, an immunologist, and professor of biomedical sciences at the University of Manchester, England.

“The type of white blood cells [las células que defienden nuestro organismo] that are in charge of that are the lymphocytes. They have the ability to recognize a germ in a very specific way and, potentially, remember it.”

Lymphocytes can recognize a particular infection before we develop it in our body.

“Some of them make antibodies that can remain in our body for a long period of time,” he says. Marc Jenkins, Director of the Center for Immunology (CBI), University of Minnesota School of Medicine, United States.

“Thus, if we get infected again or get a vaccine, these antibodies can eliminate the infection immediately, before we develop symptoms, so we have immunity,” adds the academic.

“That is very, very important because there is a phase in which you have what is called “protective immunity” —This part of the immune response can help kill the germ — and then the memory cells (or T cells) remember what has happened and know how to fight it in the future, ”says Cruickshank.

But how long do they stay in our body?

The answer varies depending on the disease.

Antibodies are key to fighting infection. (Photo: CHRISTOPH BURGSTEDT / SCIENCE PHOTO LIBRARY)

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“There is evidence that, during the Spanish flu epidemic (1918-1920), the memory cells of some people were able to produce antibodies up to 50 or 60 years later,” says the immunologist.

“However, as we get older the ability of those cells to remember those germs may also fade because our immune systems become less effective.”

When that happens, our body no longer recognizes the pathogen and, therefore, doesn’t know how to fight him.

Like an arms race

But not everything has to do with how your immune system evolves: “Infections evolve too,” says Cruickshank.

“Many of them have developed strategies to hide of our immune system, and they can do it in many ways: by hiding inside our cells; ‘stealing’ human proteins to resemble them; transforming with fragments of our information … They have many strategies ”.

And when they use them, our immune system has a harder time fighting the infection.

“It is very complex, it is as if it were a constant arms race between our immune system and those germsCruickshank illustrates.

According to the expert, there are certain germs that, or we have not discovered what is the best way to develop protective immunity against them, or we cannot.

And he gives us an example of malaria, a disease for which we do not develop permanent immunity.

“It is common for a person to be well protected from it, but go elsewhere, come back years later and lose that immunity, being as vulnerable to it as if they had never been exposed.”

Cruickshank says that this occurs because the parasite has mutated, but also due to the fact that this particular disease requires a very complex immune response, with many phases in our body for the fight to be effective.

Viruses commit “mistakes”

“Viruses have genetic material (RNA or DNA) that replicate in our body to cause infection. In doing so, they make mistakes, to a greater or lesser extent. AND those errors can change the structure of the virus explains Professor Jenkins.

It is what we also know as mutations.

Some viruses make many mistakes when replicating their genome and that complicates our reaction to them because they transform. (Photo: Getty Images)

“Some viruses, such as those of influenza (flu), have a very sophisticated mechanism to mutate. They make a lot of mistakes and can randomly change their genetic information, “adds the immunologist.

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“That is a problem for our immune system because if, for example, last year you developed an immune response to a certain form of the virus, and it mutates and changes, that response is no longer good for that type of virus. That is why a new vaccine is needed every year ”.

Viruses that can easily change their genetic material – such as influenza or HIV – have been problematic for developing vaccines in the past, Jenkins says.

What about COVID-19?

“What we know so far about the new coronavirus is that does not make many mistakes when replicating. That is something without a doubt positive for us because, historically, in this scenario, we have been able to develop good vaccines, ”Jenkins tells BBC Mundo.

“But we still cannot say so”, adds the immunologist. “How mutable is the coronavirus?¿CHow easily can you change your genetic material? That is going to be key ”.

That is also for Cruickshank the big question about COVID-19, which will allow us to find out whether or not we are capable of developing a long-term immune response.

“SARS-CoV-2 appears to behave in a similar way to SARS, which is good because there is evidence that we have immunity if we are exposed to it, but we still don’t know for sure.”

“That does not mean that we have long-term immunity against COVID-19,“ Says the immunologist.

“Hopefully so, but we still don’t know.. Only with more time will we be able to know if we are still protected several months later ”.

We still don’t know if our immune reaction to the new coronavirus is permanent. (Photo: Getty Images)

What we do know, says Cruickshank, is that our bodies respond to the new coronavirus by manufacturing three types of antibodies —AGM (the most generic); AGG (better and more powerful); and AGA (the most important) – whose levels are gradually decreasing.

And not it should come as a surprise that antibody levels drop. In fact, if they didn’t, it would be dangerous.

“All ‘normal’ immune responses have that trend curve: we make a lot of antibodies between the weeks and a month after infection, and then those levels drop after two to three months,” he explains.

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“But this decrease does not mean that we stay at zero, but at a stable level that could even give us permanent immunity,” he clarifies.

“I have been studying immune responses for many years and that decline is totally predictable”.

“That is the critical part of our immune response: it is designed to react when it needs to, and deactivate when it must,” explains Cruickshank.

“We are not interested (nor do we need) that the body continues to generate antibodies because that could have an inflammatory effect, very harmful to our body. In fact, in some patients with COVID-19, the immune reaction is exaggerated, and that is why they get very sick. ”

The importance of the vaccine

“Vaccines replicate an infection to give the immune system the information it needs to be able to generate long-term protective immunityCruickshank explains.

“Scientists from around the world work very hard to find out the strategies of the new coronavirus in our body and to know if we can have permanent immunity against it. We are learning more and more about him at a spectacular rate. That gives me hope that, in the end, we will win the battle “says the immunologist.

The Covid-19 vaccine, even seasonal, could save many lives. (Photo: Peter Dazeley / Getty Images)

Both scientists warn about misinformation and the risk that would imply that, once an effective vaccine was found, part of the population would not want to apply it.

“That would mean that our fight against the coronavirus would not be as effective, because we will need many to get vaccinated to protect those who cannot do it, or older people, for whom its effect could be less,” says Cruickshank.

“Vaccines are one of the safest drugs out there. Thanks to them we have globally eradicated infections such as smallpox, and practically also polio (poliomyelitis), ”adds Jenkins.

“When we have an effective vaccine against the coronavirus, even if its effect is temporary, such as seasonal flu, it will be necessary for as many people as possible to be vaccinated to be able to fight the infection and prevent more deaths and serious illnesses.”

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