Can you get sick again with COVID-19?

In the early 2000s, humanity was already facing an epidemic caused by the coronavirus. Then it was severe acute respiratory syndrome (SARS, English SARS) – a respiratory viral disease caused by the SARS-CoV coronavirus. When scientists analyzed the health status of people who had been ill with SARS (SARS), they found that specific immunity to coronavirus lasts an average of about 2 years. When the world faced a new coronavirus infection SARS-CoV-2, which causes the development of a dangerous disease – COVID-19, many immediately assumed that the situation with acquired immunity would be about the same. But it turned out that with the new coronavirus, everything is not so simple.

Immunity and SARS-CoV-2

Immunity to SARS-CoV-2 can be natural or vaccine-induced. The first develops after a person has been ill and the immune system “remembers” the causative agent of the disease. In this case, the body produces immune cells and proteins that can recognize and destroy the pathogen if it reappears. As a result, a person can either avoid a recurrence of the disease, or the disease will be easier. In the presence of natural immunity from a repeated disease, the body is protected by several types of cells at once:

• antibodies – proteins circulating in the blood, they are able to recognize foreign bodies, including viruses, and neutralize them;
• T cells – recognize pathogens and destroy them;
• B cells – produce new antibodies when the body needs them.

Researchers have found that people who have recovered from the new coronavirus disease have all of these components in their bodies. But how long they last and provide proper protection is not known – so far too little research has been done to draw unambiguous conclusions.

One recent US study suggests that despite high variability in immune response, immune memory to SARS-CoV-2 can last up to 8 months. ^[1]. A few months earlier, another group of scientists from the United States conducted similar studies and concluded that antibodies to SARS-CoV-2 in the blood of those who have been ill persist for at least 3 months, even in the case of a mild form of the disease. ^[2].

Icelandic experts also studied the question of how long antibodies remain in the blood of those who have recovered from COVID-19. Among 1215 people who recovered from coronavirus infection, antibodies were determined in 1107. Scientists continued to measure the antibody titer and found that even 4 months after the disease, the number of antibodies in them practically did not decrease ^[3]. And scientists from the United States, starting in the spring of 2020, studied the analyzes of almost 30 thousand Arizona residents and discovered that even in people who have had a mild form of COVID-19, the production of antibodies continues for at least 5-7 months, although the production of antibodies in the case of a more severe disease progression is markedly higher. ^[4].

With regard to immunity obtained after vaccination, it allows the body to produce antibodies without prior infection. After vaccination, a sufficient number of B- and T-cells are produced, which, if infected, will be able to resist the virus. But, as a rule, several weeks must pass from the day of vaccination in order to develop a sufficient number of cells to protect. While they are not there, a person is just as vulnerable as before vaccination.

Despite the fact that today there are several vaccines against the new coronavirus in the world, so far no one can say for sure how long immunity will last after vaccination. Moreover, the virus, as it turned out, is prone to mutation, and several strains of SARS-CoV-2 have already been detected. Even more, it is already clear that the South African strain is more resistant to Novavax and Johnson & Johnson vaccines than other strains of the new coronavirus. ^[5].

Is the presence of antibodies a guarantee of protection against re-infection?

Experts say that antibodies appear in almost every body after contact with SARS-CoV-2. In some individuals, they appear already within the first week after the onset of the disease. But there are different types of testing that aim to detect different types of antibodies. ^[6].

For example, some tests detect the nucleocapsid protein found in the coronavirus, while others recognize antibodies that protect against the coronavirus spike protein.

However, a positive antibody test still does not give a clear picture of the body’s resistance to the virus. In particular, experts remind that in some infections, antibodies can indeed protect against re-infection, while in others, re-infection is possible, but the symptoms will be milder. However, there are cases when antibodies are not at all protection against re-infection. In addition, false-positive antibody test results occur, in which it is also easy to get infected. ^[7].

Re-infection with COVID-19: is it possible?

Today, cases of re-infection with the SARS-CoV-2 virus, although they remain not very common, do occur. In particular, a group of scientists conducted a study among health workers in the UK. A total of 50 people took part in the study. Participants in the study were tested for antibodies to SARS-CoV-12 every 2-4 weeks for 2 months. The first test showed that about a third of the participants had antibodies to the virus, which confirmed the infection of people in the first wave of the pandemic. Then, over the next 5 months, approximately 1% of people in the antibody group were re-infected with COVID-19. Moreover, reinfection occurred both in those who were asymptomatic in the first wave, and in those who suffered the disease in its full manifestation. In addition, during the study, scientists found that in some people, antibodies after illness persist for a very long time, while in others they disappear quickly. ^[8].

Cases of re-infection have also been reported in South Africa. True, vaccination can reduce the severity of the disease. ^[9]. Similar cases continue to be recorded in different countries of the world.

The main problem is that until now, scientists know too little about the mechanism of re-infection with COVID-19. In what cases can re-infection occur, who is at risk, how severe is the re-infection, what does reinfection mean for immunity, and how soon after the first case of the disease can the second occur? These are questions that experts do not yet have answers to. This means that all of us – healthy, recovered, vaccinated – remain at risk, so we must not lose vigilance and ignore prevention.

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