Can you get coronavirus twice?
Why do some people have more severe symptoms than others?
Will there be a recurring epidemic each winter?
Does the vaccine help?
Can you go back to work with a certificate of immunity?
Is there a long-term strategy to control the virus?
And the most important question on everyone’s mind today is what role does our immune system play in this new reality?
The problem is that very little is known about it. Our immune system is the body’s defense against infection, and it consists of two parts. The first is innate immunity. It rushes into battle as soon as it detects a foreign element in our body. This process involves the release of chemical elements that cause inflammation, as well as white blood cells capable of destroying infected cells. But in the case of coronaviruses, a different component is needed – acquired immunity, which involves two mechanisms.
The first is the ability to produce antibodies that attach to the virus and limit its spread in the body. The second is the presence of T lymphocytes, which recognize and attack infected cells. It takes time for the acquired immunity to become active – according to research, it takes about 10 days for the body to start producing antibodies against the coronavirus, after which the most severely affected patients develop a strong immune response. The stronger the collision between acquired immunity and infection, the greater the likelihood that a person will be protected from reinfection with the same virus in the future.
At present, it is not known whether those who have had a mild form of the disease or who have been asymptomatic can develop a sufficiently robust mechanism to counteract future infections of the same type. Scientists believe that the more severe the disease, the greater the chance of developing immunity to it in the future. The immune system’s memory is similar to our own: it remembers some infections well, but can forget others.
Measles is well remembered; once you have had it, you get immunity for life (the same effect is provided by the combined MMR vaccine against measles, mumps, and rubella, which is a mixture of their weakened antigens). However, many other diseases fall out of the immune system’s memory. For example, a child may contract the respiratory syncytial virus HRSV several times during the course of a winter. The new coronavirus Sars-CoV-2 has emerged relatively recently, so it is not yet known how long it will persist in the immune system’s memory. However, the other six coronaviruses that can infect humans may provide clues. Four of them cause symptoms similar to the common cold, and our immune system does not remember them: research shows that some patients are re-infected with them within a year.
The development of a vaccine depends on the characteristics of immunity. However, a common cold is usually easily tolerated. However, there are two other problematic coronaviruses that cause Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). The antibodies produced in the body to fight these diseases do not disappear, even after several years. “The question is not whether you develop immunity, but how long it lasts,” explains Paul Hunter, professor of medicine at the University of East Anglia. “And almost certainly it will not last a lifetime.”
“Based on the experience of studying antibodies in SARS, immunity will last for one to two years, but we definitely do not know that yet,” Professor Hunter adds. However, even if you do not have full immunity, there is a possibility that a subsequent illness may not be as severe. There is information about people who appear to have had multiple coronavirus infections in a short period of time. Some believe that these people were actually infected with the coronavirus twice. Others believe that the infection occurred once, but the virus remained latent in the body, only to be reactivated later. However, the majority of scientists agree that it’s all about the tests: patients are simply misinformed that they don’t have the virus.
None of the humans were re-infected to see if they had developed immunity, but a pair of rhesus monkeys were less fortunate. They were infected twice: once to induce an immune response, and again three weeks later. Although the experiment was very limited, neither monkey showed any symptoms of the disease after the second infection with such a short interval.
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This is still not a guarantee, which is why the WHO is so concerned about countries that have introduced immunity passports to lift quarantines. The idea behind this innovation is that those who are tested and found to have antibodies to Covid-19 could be allowed to return to work safely. This would be particularly useful for nursing home and hospital staff who are constantly in contact with people at high risk of developing serious illness.
Although almost everyone has antibodies in their blood, not everyone has the same antibodies. Neutralizing antibodies are needed to attach to the coronavirus and prevent it from infecting new cells. However, a survey of 175 recovered patients in China showed that 30% of them had critically low levels of such neutralizing antibodies. Therefore, according to the WHO, immunity at the cellular level may also be a critical factor in recovery.
Another important point to remember is that even if you are protected by your own antibodies, it does not mean that you cannot be a carrier of the virus and thus a danger to others. This is a question of your health and whether you can become infected with Covid-19 again and how often this will happen. The mortality of this disease also depends on immunity. If people have at least partial immune protection, the disease will be less dangerous.
Understanding the principles of immunity will help to better address the issue of lifting quarantine measures, as medical professionals will have a better understanding of who is not at risk of infection and who will not become a carrier of the infection. If it proves difficult to develop long-term immunity to the virus, it will also be difficult to develop a vaccine against it. Alternatively, the vaccine might be different: for example, it might need to be administered every year, like the flu, rather than once in a lifetime. And the duration of immunity itself, whether developed during the current illness or through vaccination, will tell us whether we can contain the spread of this virus. Unfortunately, there are still no answers to all of these important questions.