COVID-19 Immunity: Key Questions About Antibodies and Reinfection Risk Answers

When it was revealed at the beginning of the year that the causative agent of a mysterious disease in China is a new coronavirus, scientists' concern about the growing epidemic in the country almost gave way to despair. As a rule, representatives of this family of viruses do not form strong immunity in those who have been ill: already six months or a year after recovery, the same infection can easily be picked up again, writes Air force.

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However, the more we learn about the new virus, the more we are convinced that Sars-Cov-2 is very different from its predecessors. This means that there is hope that immune protection in recovered patients will be much longer-term—perhaps even lifelong.

However, so far this is only an assumption. The main questions on which the strategy to fight the epidemic depends remain unanswered.

The BBC Russian service says that scientists have learned about immunity to COVID-19 in the six months since the beginning of the pandemic, and also why most researchers of the virus and vaccine developers against it are rather optimistic.

What is immunity in general

Immunity is the body’s ability to resist infection, that is, to protect against a particular disease by neutralizing its causative agent (virus, bacteria or fungus).

Immunity is divided into congenital, that is, inherited from our ancestors (it allows us to fight diseases in general), and acquired, which is formed after birth as a result of an encounter with a specific infection (and protects only from it).

Having first encountered the causative agent of any disease, our body develops a strategy to combat it - and at the next meeting it immediately puts up effective resistance. In fact, this means that our body can remember and recognize past illnesses after some time.

Often, the immune memory (as scientists call this phenomenon) stores memories of events that have long been erased from ordinary memory.

For example, you yourself hardly remember how in early childhood you had chickenpox or were vaccinated with BCG, but your immunity remembers this and prevents you from getting sick again - it neutralizes particles of the chickenpox virus (or Koch bacilli) that have entered our body.

How long does immunity last?

The duration of immune memory depends on the disease. Chickenpox, mumps, or measles most often leave behind lifelong immunity (this is the exception rather than the rule).

Vaccinations that protect against hepatitis A or yellow fever are recommended to be repeated every 10 years.

Contrary to popular belief, seasonal influenza also forms a strong immunity in the patient - however, only to the very variety (strain) of the virus that the person suffered from.

The flu quickly mutates, so that after a few months a person can get it again. However, in this case, the disease is often mild, since antibodies to the previous infection provide partial protection to the patient (more on this below).

What are antibodies and how do they work

The body selects the key to any new infection by trial and error.

Imagine that each viral particle is a dagger with a bizarrely shaped blade, and your body is a sheath production factory. Each line in this plant produces the same shaped cases, but together they provide an almost infinite variety of sizes and configurations.

As soon as one of the cases matches the shape of the dagger and the blade has been hidden, all the free conveyors of the plant immediately begin to produce scabbards of the same shape on an industrial scale - and sooner or later all the daggers can be secured.

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In this case, each conveyor is a specific blood cell (the so-called B-lymphocyte), and the scabbard is the protein molecules (antibodies) produced by this cell. When one of the molecules fits the shape of the “blade” - the spike protruding on the surface of the coronavirus - it seems to be pushed onto it from above, changing the shape of the spike and thus preventing the virus from entering the cell.

But outside the cell, the virus cannot multiply: in order to stamp its own copies, it needs its building materials. Therefore, the growth in the number of viral particles slows down.

At the same time, the body receives a signal that one of the antibodies has managed to neutralize the invader, and launches molecules of a similar shape “into mass production.” When the spikes on all viral particles can be blocked, the person recovers.

Will all patients have the same antibodies?

Not necessary, because the same dagger can be sheathed in different sheaths.

For example, the sheath cannot be shorter than the blade or have a narrower opening than the width of the blade itself, but the sheath may well be a little longer and the hole a little wider.

In the blood of COVID-19 patients, scientists have found a total of more than 250 types of antibodies produced by the patients' bodies in an attempt to stop infection. 28 of them fought the disease (that is, neutralized the virus) most effectively.

What Happens After Recovery

Unclaimed cases “go into storage”: antibodies remain in the blood and continue to patrol the body in case of re-infection. This is why they can be found in recovered patients weeks, months and even years later (see above).

Some of the B-lymphocytes are converted into so-called memory cells. When they re-encounter an infection, they activate and re-start the well-oiled conveyor, thereby providing a quick immune response.

However, this does not mean that such a person is protected from re-infection. The strength of the immune response depends on both the severity of the illness and the time elapsed after recovery.

The more severe the disease progresses, the stronger the protection against re-infection will be. The more time has passed since recovery, the less effective the immune response will be.

Is it true that people who have not had COVID-19 may be immune to the virus?

In theory, this is possible. As mentioned above, antibodies to coronavirus (as well as to other diseases) come in different forms. Some of them may be effective against more than one infection.

For example, in blood samples donated by healthy people long before the start of the epidemic, antibodies were found that can effectively neutralize the new coronavirus Sars-Cov-2, although they were originally developed as a protection against some other disease.

The mere presence of such antibodies does not mean that people have effective immune defenses. However, this increases the likelihood that COVID-19 infection in such people will be milder.

However, the opposite is also possible. The fact is that the new virus itself is not too dangerous for the body - the main problems for the health of patients are created by their own immune system.

The most dangerous symptoms in seriously ill patients begin to appear precisely after the development of antibodies to COVID-19. And it is possible that the presence in a person’s blood of similar antibodies to previous diseases can only intensify infection - intensifying the aggressive immune reaction (the so-called cytokine storm) and complicating the course of the disease.

Only antibodies provide immunity from coronavirus?

The simple answer is no. In addition to antibodies, other agents also take part in the fight against infection, including so-called T cells (or T lymphocytes), which are also involved in the formation of immune memory.

Moreover, judging by the latest data, T cells play no less, and maybe a greater role in the immune defense against COVID-19 than antibodies to coronavirus, since the lifespan of T-lymphocytes is much longer.

As in the case of antibodies, which can provide partial protection against a new virus, despite the fact that they remained in the body after fighting another infection, T cells can exhibit similar properties and effectively neutralize the causative agent of COVID-19, even in people who have not been met with him.

This may be one of the explanations for why some patients experience the disease in such a severe form, while in others, COVID-19 is able to cause no symptoms at all: some of us may be partially protected by the immunity left after previous diseases.

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The fact is that the common cold is caused by four different viruses belonging to the same “crowned” family (coronaviridae). So, in the body of many people who have had a cold over the past couple of years, there is a high probability that there are either antibodies to one of these coronaviruses, or T-cells that remember the previous infection.

This phenomenon is called cross-immunity and, according to some reports, almost every third person has such nonspecific T cells, and together with antibodies, up to half of the world's population can have partial protection against COVID-19.

In addition to T-lymphocytes and antibodies, there is another protective mechanism that scientists have been increasingly talking about in recent years - the so-called trained innate immunity.

As mentioned above, hereditary immunity is not specific, that is, it is not directed against any specific infection. However, more and more studies indicate that he also has the ability to remember past illnesses - albeit not for so long.

Macrophages, monocytes and natural killer cells are more effective in neutralizing viruses and bacteria with which they have already met before, and can even protect against other pathogens completely new to the body.

Can you get COVID-19 again?

So far, no reliable case of re-infection with coronavirus is known. Scientists do not exclude that this is possible, but in the context of all of the above, the likelihood of such an infection is not very high.

Research shows that after recovery from COVID-19, specific antibodies are found in the blood of most patients - even in those who were asymptomatic.

As in the case of many other viral diseases, their concentration is higher in those who have had the virus in a severe form, but in any case, it begins to fall after three months, and sometimes after several weeks.

Since Sars-Cov-2 was first discovered only seven months ago, scientists have so far refrained from making predictions about how long acquired immunity lasts or whether reinfection is possible in principle. However, some conclusions can be drawn based on its more studied predecessors and close relatives - the SARS (SARS) and MERS (Middle East Respiratory Syndrome) viruses.

In the blood of patients who recovered from SARS in 2002-2003, specific antibodies to the virus persisted for an average of two years (to be more precise, from a year to three). Although in people who have had severe SARS, they were found even 12 years later.

Patients with Middle East respiratory syndrome (an average of every third infected die from it) retained specific antibodies to the MERS virus for at least 34 months.

And while scientists do not know how long the immune protection against COVID-19 will last and how effective it will turn out to be, this very fact inspires optimism. The longer they don’t know the answer to this question, the more likely it is that reinfection is impossible.

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