Why get a booster dose?

From 24 January, people and children over 12 years of age can get a booster dose after 5 months after the completion of vaccination.

We have only known about COVID-19 since December 2019, and although it is the subject of intense research by scientists around the world, we still don’t know everything about it. The same applies to vaccination against this disease. How long the protection lasts after vaccination and when it is appropriate to re-vaccinate can only be determined after a certain period of time by monitoring vaccines in clinical trials. This applies to all vaccinations. It usually takes several years to set up the best vaccination schedule.


Since the launch of the COVID-19 vaccination, a number of studies have been conducted worldwide. The results from some of these studies show that approximately six months after vaccination, the effectiveness of protection decreases and therefore the likelihood of a breakthrough infection, i.e. infection in the vaccinated individual, increases. This likelihood is further increased by the emergence and spread of new SARS-CoV-2 variants, which were not known at the time of the vaccine development and which can partially bypass the protective mechanisms established after vaccination and possibly cause the disease.

Other studies point to the risk that protection declines more quickly after vaccination in older people or in those with weakened immunity or chronic illnesses. Again, this is not unusual, as this phenomenon is also observed in vaccinations against other diseases. In order to prevent an increase in breakthrough infections, especially in people in high-risk groups such as immunocompromised, chronically ill or elderly people, it is advisable to vaccinate these groups to strengthen their protection against COVID-19. These people are most at risk of a decline in protection against COVID-19 and, above all, sooner than others. Vaccination is also appropriate for people who may be at risk of contracting COVID-19 or who are at a higher risk of contracting the disease as part of their employment. These include people working in healthcare or social services.

What are the benefits of the booster vaccination dose?


The main advantage of the vaccinated over the unvaccinated is their protection from the COVID-19 disease, especially from its severe course, or from hospitalization or death related to the COVID-19 disease. Even though cases have been described in properly vaccinated persons, the likelihood of contracting the disease and the risk of severe disease is significantly lower than in unvaccinated persons.

The administration of a booster dose will reduce the likelihood of a possible infection and its severe course many times over, thus ensuring greater health protection for those at risk. Some studies have reported that after a booster dose, the level of protective antibodies increases by 5 to 11 times more than after a second dose. In addition, this boost in immunity occurs very quickly, usually within days. After the first dose, it takes up to three weeks for the body to respond to the vaccination by producing antibodies. However, the antibody response alone is not sufficient to assess the effectiveness of vaccines and therefore it is necessary to wait for the results of clinical trials.

Since the length of protection after vaccination varies from person to person, no one can predict with certainty how long they will be protected to the greatest extent possible. Therefore, as soon as it is possible for a given group of people, the use of vaccination is the best we can do against the COVID-19 infection.

Does the booster vaccine also protect against new coronavirus variants?

The significant increase in antibodies following the booster dose will also enhance protection against previously-known new variants of the virus, such as the omicron variant. The omicron variant was not known at the time of research into current vaccines and although vaccination provides some protection against it, this protection is lower than that of previously circulating variants of the virus. However, the administration of a booster dose should provide sufficient protection against this variant.

So vaccination is not the end of coronavirus?

Vaccination is the most effective way to reduce the spread of coronavirus and COVID-19 in the population and to protect the health of as many people as possible. No other measure has the same impact as vaccination. However, how the Tečka (i.e. end of the pandemic) will be achieved through vaccination is still under investigation. According to the results of studies, protection against the COVID-19 disease after vaccination decreases over time, and therefore it will be necessary to use booster doses in people at risk to increase and maintain it at the highest possible level. It is not uncommon to administer multiple doses of a vaccine to provide sufficient protection against an infectious disease. For example, the tick-borne encephalitis vaccine consists of three doses in the first year and then regular re-vaccination at intervals of three to five years. Influenza vaccinations are given every year, with vaccines being modified according to the currently circulating strains of the influenza virus to make them as effective as possible. The most effective vaccination schedule for COVID-19 is still under investigation. A number of scientific studies will need to be carried out to determine whether a third dose alone will be sufficient or whether additional doses of vaccination will be needed, and the development of cellular and antibody immunity in vaccinated persons will need to be carefully monitored.

Of course, for the COVID-19 vaccination to be the true Tečka (end) of all lockdowns, restrictions and masking, as many people as possible need to be vaccinated. According to current data, vaccinated people are not only less likely to become infected, but also significantly less likely to infect someone else, according to epidemiological surveys.

Why not wait until a modified vaccine is available to vaccinate?

As the number of confirmed cases is now gradually increasing again and new variants of the coronavirus are spreading, a further deterioration of the epidemic situation can be expected during the autumn. It is therefore necessary to do everything possible to protect the most vulnerable groups in particular. These are mainly elderly people, people with immune disorders, but also with various chronic diseases. Most of these people from at-risk groups were already vaccinated at the beginning of 2021, more than half a year ago. It can therefore be assumed that some of them have experienced a decrease in protection after vaccination and could be at risk of contracting COVID-19 in the event of another epidemic wave. As the vaccination coverage in the Czech Republic is still not high enough, there are still a large number of people who can spread the disease and infect vaccinated people, including people from risk groups. To prevent this from happening, post-vaccination protection needs to be strengthened, not only for people in at-risk groups, but also for healthcare workers, social care workers and any other vaccinated people who express an interest in strengthening their protection.

It is not yet clear when vaccines modified to protect against the new coronavirus variants will be available in the Czech Republic, probably not before the expected autumn wave. And since the number of people in the Czech Republic, especially from at-risk groups who were vaccinated more than 8 months ago, will start to increase in October, it is necessary to take advantage of the options currently available to protect them as much as possible. This is a booster dose of one of the mRNA vaccines (Spikevax/Moderna, Comirnaty/Pfizer).

It is difficult to predict how vaccination will develop in the future. If new variants of coronavirus continue to spread, it is possible that additional doses of vaccination may be needed in the future, possibly with modified vaccines. However, there is insufficient data to answer this question at this time.

Why is it suddenly possible to combine vaccines when vaccinating?

Information on vaccination evolves over time. The more experience we have with vaccination and the more vaccines that can be monitored and continuously investigated, the more data can be used in practice. The vaccines that have been gradually developed in the world and in the Czech Republic were thoroughly tested before their introduction to the market. Each pharmaceutical company, of course, has exclusively tested its own vaccine under development and, based on its research, has set up the most appropriate vaccination schedule, which it has included in the Summary of Product Characteristics. Only over time, when more vaccines became available, did it become possible to start studies on their possible combination. The results of these studies are gradually becoming available. The most ideal vaccines for re-vaccination seem to be the so-called mRNA vaccines (Spikevax / Moderna, Comirnaty / Pfizer), both because of their high efficacy and because they are easier to modify in relation to new coronavirus variants. At the moment, these two vaccines are the only vaccines allowed for re-vaccination by the emergency measure of the Ministry of Health.

A combination of vaccines is also possible in case of the uneven distribution of vaccines in the Czech Republic. This is particularly the case when the person seeking a booster dose does not have a vaccination site near their home that offers the vaccine with which they were originally vaccinated.

However, for basic vaccination, the preferred option is still to be vaccinated with the same vaccine.

Frequently asked questions regarding COVID-19 vaccination can be found here.