The announcement that an effective and safe COVID-19 vaccine has been developed was one of the most anticipated news of the last few months. Studies have shown that some vaccines can be as effective as more than 90% effective, protecting against the development of severe COVID-19 disease. However, despite this, we still do not know, for example, whether a person vaccinated with COVID-19, after contact with the SARS-CoV2 coronavirus, can infect other people?

Immune response to the COVID-19 vaccine

The COVID-19 vaccine is designed to induce mainly an immune response so that IgG antibodies against the SARS-CoV2 coronavirus are produced. This is to prevent the virus from spreading throughout the body and the development of a severe form of COVID-19.

IgG antibodies are the dominant group of immune proteins in our body. They are produced by B lymphocytes specifically against certain proteins in a virus or other pathogen. By sticking to the surface of the virus, they neutralize it and allow it to be safely removed from the body by the cells of the immune system.

However, such a vaccine mechanism is systemic and does not necessarily stimulate the respiratory mucosa response, which is the primary gateway for coronavirus entry.

In the mucosa, on the other hand, specific IgA antibodies play a key role in neutralizing the coronavirus, which do not have to be produced following COVID-19 vaccination.

Preclinical studies have shown that the coronavirus can be detected in nasal swabs of vaccinated people, even though they have not developed symptoms of COVID-19. This suggests that vaccinated people, despite not having symptoms, may be susceptible to infection by spreading the coronavirus through the respiratory tract.

Why is a person vaccinated against COVID-19 contagious with the coronavirus?

This phenomenon may be due to the fact that currently used vaccines against COVID-19 do not cause the so-called sterilizing immunity, which is achieved when antibodies (mainly IgA antibodies) neutralizing the virus bind to it, preventing it from entering the cell and multiplying.

For the COVID-19 vaccine, even though it protects againstsevere course of the disease, this does not exclude the possibility of re-entry of the coronavirus into the body of the vaccinated person. In other words, thanks to these vaccines, the immune system is "trained" to stop the outbreak of the disease, but the coronavirus can survive in the body, potentially allowing it to infect others.

A consequence of the lack of sterilizing immunity is that the coronavirus may still circulate in the population and cause COVID-19 disease in unvaccinated people. Hence, it is so important to vaccinate as many people in the population as possible.

Perhaps in the future, next generations of the COVID-19 vaccine, e.g. oral form containing an attenuated virus (unable to cause disease), will prove to be more effective in inducing sterilizing immunity.

This is because, when an oral vaccine is given, the virus, by infecting cells in the intestine, stimulates the mucosa-bound immune system and produces specific IgA antibodies. This protects the respiratory system against the negative effects of virus entry and at the same time allows the concentration of IgA antibodies to be increased on all mucous membranes.

COVID-19 vaccine is not a source of infection

The second important point to understand is that currently used COVID-19 vaccines do not contain the virus, only a fragment of it. Therefore, vaccination alone is not a source of virus in the body of the vaccinated person.

However, it may happen that a vaccinated person comes into contact with someone suffering from COVID-19 or becomes infected with coronavirus in public. Even though the coronavirus will enter her body and likely to multiply, the vaccine will protect her from developing COVID-19.

It should also be noted that most vaccines require two doses to provide us with effective protection against the development of COVID-19. Therefore, in the period between successive vaccines, not only the coronavirus infection itself may occur, but also the development of a severe form of COVID-19.

Should vaccinated people continue to follow the sanitary regime? Although available clinical trials show the effectiveness of vaccines in preventing the development of COVID-19 disease, they cannot conclusively confirm that currently used vaccines are effective in stopping the spread of the coronavirus.

Therefore, it is recommended that people vaccinated against COVID-19 still maintain social distancing, wear mouth and nose masks, and wash their hands frequently.

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COVID 19