Coronavirus immunity: Can you get it twice?

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Can you get coronavirus again? Why are some people sicker than others? Will he come back every winter? Will a vaccine work? Could immunity passports get some of us back to work? How do we handle the virus in the long term?

The immune system is at the center of some of the most important questions about the coronavirus.

The problem is that we know very little.

How do you become immune to the coronavirus?

Our immune system is the body’s defense against infection and comes in two parts.

The former is always ready to go and jumps into action as soon as a foreign invader is detected in the body. It is known as the innate immune response and includes the release of chemicals that cause inflammation and white blood cells that can destroy infected cells.

But this system is not specific to the coronavirus. It will not learn and will not give you immunity to the coronavirus.

Instead, it needs the adaptive immune response. This includes cells that make targeted antibodies that can bind to the virus to stop it, and T cells that can attack only cells infected with the virus, which is called a cellular response.

This takes time: Studies suggest that it takes about 10 days to start producing antibodies that can attack the coronavirus, and sicker patients develop the strongest immune response.

If the adaptive immune response is powerful enough, it could leave a lasting memory of the infection that will provide protection in the future.

It is not known whether people who have mild symptoms, or none at all, will develop a sufficient adaptive immune response.

How long does immunity last?

The memory of the immune system is quite similar to ours: it remembers some infections clearly, but has a habit of forgetting others.

Measles is very memorable: one episode should provide lifelong immunity (as the weakened version of the MMR vaccine does). However, there are many others that are quite forgettable. Children can get RSV (respiratory syncytial virus) several times in the same winter.

The new coronavirus, called Sars-CoV-2, has not been around long enough to know how long immunity lasts, but there are six other human coronaviruses that may give a clue.

Four produce the symptoms of the common cold and immunity is short-lived. Studies showed that some patients could become infected again within a year.

But the common cold is generally mild. There are two more troublesome coronaviruses, those causing Severe Acute Respiratory Syndrome (Sars) and Middle East Respiratory Syndrome (Mers), in which antibodies have been detected a few years later.

“The question is not whether you become immune, but how long,” said Paul Hunter, a professor of medicine at the University of East Anglia.

He added: “It is almost certain that it will not last a lifetime.

“According to antibody studies at Sars, immunity may only last for one to two years, although this is not yet known with certainty.”

However, even if you are not completely immune, a second infection may not be as severe.

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Have people caught him twice?

There have been reports of people appearing to have multiple coronavirus infections in a short span of time.

Some have argued that people are actually infected twice. Another school of thought is that the virus stealthily enters the body before being reactivated.

However, the scientific consensus is that the test is the problem with patients who were incorrectly told that they were free of the virus.

No one has been deliberately reinfected with the virus to test immunity, but a couple of rhesus macaque monkeys have.

They were infected twice, once to develop an immune response and then a second time three weeks later. Those very limited experiments showed that they developed no symptoms again after such a rapid reinfection.

If I have antibodies, am I immune?

This is not guaranteed and that is why the World Health Organization is nervous about countries that use immunity passports as a way to get out of the blockade.

The idea is that if you pass the antibody test then it is safe to go back to work. This would be particularly valuable for staff in nursing homes or hospitals who come into contact with people at risk of developing severe symptoms.

But although you will find some antibodies in almost all patients, not all are the same. Neutralizing antibodies are those that bind to the coronavirus and can prevent it from infecting other cells. A study of 175 recovered patients in China showed that 30% had very low levels of these neutralizing antibodies.

That is why the World Health Organization says “that cellular immunity [the other part of the adaptive response] it can also be critical to recovery. “

Another problem is that just because you can be protected by your antibodies doesn’t mean you can’t yet harbor the virus and pass it on to others.

Why does immunity matter?

It matters for obvious personal health reasons and if you will receive Covid-19 multiple times and how often.

Immunity will also affect the lethality of the virus. If people retain some protection, even imperfect, the disease will be less dangerous.

Understanding immunity could help alleviate the blockage if it is clear who is not at risk of contracting or spreading the virus.

If long-term immunity is very difficult to produce, it could make a vaccine more difficult to develop. Or it can change the way the vaccine should be used: it will be once in a lifetime or once a year like the flu shot.

And the duration of immunity, whether from infection or immunization, will tell us how likely it is that we can stop the spread of the virus.

These are all important questions that are still missing answers.

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