Corona Immunity: How Long do Infection and Vaccination Protect?

Through vaccinations, but also through surviving infections, people develop immunity against the corona virus. But how good is it actually and how long does it last?

SARS-CoV-2 has kept the world in suspense for over a year. Other viruses are also highly contagious and dangerous, but this virus was completely new to mankind. And this is exactly where the problem lies: all over the world, people have been naive to the virus. This means that not a single immune system had an answer to this attacker and anyone who came into contact with the virus could also get sick and pass the virus on. That is the only reason why the pandemic was able to develop as we have experienced in recent months.

Does a past infection protect?

Through vaccinations, but also through surviving infections, people develop immunity against the virus. But how good it actually is and how long it lasts is still the subject of research. A study from Denmark has shown: people who have already contracted Covid-19 are 80 percent protected from reinfection. In the over-65s, however, this was only the case for 47 percent - presumably because the immune system no longer works as well in older people as it does in younger people. Because like the body as a whole, the immune system also ages. It can no longer react so quickly and so well to pathogens. It is therefore important to vaccinate people who have already been infected with SARS-CoV-2. The vaccination strengthens the immune response and thus improves protection against reinfection.

How the immune system reacts to the virus

When infected, the virus penetrates the body cells in order to multiply there. The innate immune system reacts to this first: phagocytes recognize the intruder as foreign, destroy the infected cell and then present components of the virus on their surface. This activates the specific immune system: B cells dock on the presented corona virus proteins and form suitable antibodies that can prevent further corona viruses from penetrating body cells.

How many antibodies are formed depends on the severity and duration of the disease. The more seriously someone was sick with Covid-19, the more antibodies they usually produced. In the course of time, however, the number of antibodies decreases again in everyone who has recovered. Similar to B cells, T cells also attach to the virus proteins presented by the phagocytes. They form substances that find and destroy other cells in the body that are already infected. As long as the infection is active, these processes continue to run and more and more T and B cells are fighting the virus. After infection, they gradually disappear from the blood - except for the so-called memory cells. If there is new contact with the virus, they immediately recognize the attacker and ensure fast, effective defense.

How long does natural immunity last?

So far, scientists have assumed that immunity to SARS-CoV-2 will last for at least four to six months after an infection, even if this has not been proven. However, it will almost certainly prevent severe courses for a long time. It is still unclear whether a passed infection can also protect against virus variants.

How long does the vaccination protect?

Since they have only been vaccinated in large numbers for a few months, it is not yet clear how long the immunity achieved with the vaccines actually lasts. However, according to the data so far, experts assume that a vaccination will work safely for at least six months. It is not yet possible to estimate how well the vaccines and infections protect against future virus variants. Regular booster vaccinations with vaccines adapted to the new variants may be necessary - similar to the flu vaccination. It can already be seen that vaccinated people - depending on the vaccine used - are very well protected from the British, but less well protected from the South African and Brazilian variants. These have mutated so strongly that the immune system cannot recognize them properly despite being vaccinated.

Basic immunity increases with the number of people vaccinated

The more people have been vaccinated or recovered, the more likely it is that basic immunity against SARS-CoV-2 will develop worldwide. Then billions of immune systems will at least have a clue what SARS-CoV-2 is and how it can be combated. In this way, they can react more quickly to new virus variants and significantly fewer sick people, severe courses and deaths are to be expected.