FAQ: Why vaccination breakthroughs occur


Status: 11/12/2021 6:35 p.m.

The number of corona infections is rising again and more and more people have to go to hospital – including those who have been vaccinated. Why is that? How well does the vaccination protect? Here are the most important questions and answers.

By Veronika Simon, SWR science editor, and Anja Martini, tagesschau

How many people have been hospitalized?

More and more patients are currently being admitted to hospitals with a Covid-19 infection. According to the Robert Koch Institute, the numbers are increasing in almost all age groups. The group of people over 60 is particularly affected. In reporting week 40 (October 4th – 10th) there were 1388 hospitalized people in this age group out of a total of 2535. Four weeks later, 2907 people out of a total of 4407. The numbers also increased noticeably among 35 to 59 year olds. In calendar week 40 there were 759 patients and in the 44th calendar week 957 patients.

Christian Karagiannidis is the medical and scientific director of the DIVI intensive care registry and speaks with us in an interview tagesschau24 from two groups that can now be seen more and more in intensive care units: on the one hand, there are younger, unvaccinated people and, on the other hand, older people with a weakened immune system and without a booster vaccination.

Since July 13, hospitals have not only had to report the admission of Covid-19 cases, but also suspected COVID-19 illness and death to the health department. However, the number cannot be recorded precisely because reports are always late. Inaccuracies in the RKI report are also caused by subsequent submissions when the condition of Covid 19 patients only worsens after a few days and they then have to go to the clinic.

How many people are affected by vaccination breakthroughs?

The number of people who get the coronavirus despite being vaccinated is also increasing. According to these data, there have been 175,188 probable vaccination breakthroughs in Germany since the start of the vaccination campaign. The President of the Society for Immunology, Christine Falk, explains at tagesschau24that with 56 million vaccinated people this is only 0.3 percent of those vaccinated who apparently had a vaccination breakthrough. And of the total number of vaccine breakthroughs, only about four percent would have to go to hospital. In all other cases, the vaccinated would have such an easy course that they did not have to go to the clinic. That shows how effective the vaccines are.

Why are there vaccination breakthroughs at all?

It was already known after the approval studies that people would become infected even though they were vaccinated. The vaccines showed a very good effect, but none of the vaccines had an effectiveness of 100 percent in the studies. Such breakthroughs in vaccination are normal and are also known from other vaccines.

The fact that the number of such breakthroughs after the Covid vaccination is currently increasing is also due to the fact that many no longer adhere to hygiene rules so strictly, says Katherine O’Brien. The immunologist heads the WHO immunization and vaccination department. However, the safety precautions are important to keep the spread of the virus in check: “If the virus spreads faster and further, then we come into greater contact with it – this also affects people who have been vaccinated.” In rare cases, they could also fall ill.

How long does the vaccination last?

It has now been shown that the protection afforded by vaccination decreases over time. According to a British study, the longer it has passed since full immunization, the higher the likelihood of falling ill despite being vaccinated. Because the antibody level that the body has built up against the coronavirus drops some time after the vaccination. However, this does not leave the body defenseless. Because the immune system consists of other defense cells that are activated by the vaccination. In this way, the immune defense can be reactivated relatively quickly, even if the antibodies are barely measurable after a few months.

Why can people who have been vaccinated also become infected and pass the virus on?

A vaccination protects against a severe course of Covid 19 disease – but it does not protect people who have been vaccinated from becoming infected. Immunologist Falk explains that the antibody defense in people who get a breakthrough vaccination may not be completely complete. This could allow the virus to get into the throat and then infect the vaccinated person. However, the second level of defense, that of the T cells, then sets in. However, they need a little time to become really active. In this time window of around two to three days, the viral load could be relatively high. However, this then drops again because the T cells prevent the virus from spreading in the body. For this reason, breakthrough infections often lead to mild courses of the disease.

Who is particularly affected?

Not all people have the same risk of developing Covid-19 despite being vaccinated. People with a weakened immune system are particularly affected, explains O’Brien. This can be the case, for example, after an organ transplant or during cancer treatment. But the risk of a vaccination breakthrough also increases with age. The reason for this is that the immune system becomes more inflexible with age and learns more difficultly how to ward off previously unknown pathogens. As a result, the vaccination does not work as well or not at all, and no long-term protection can be built up.

How does an immune response work?

The vaccination stimulates the body to produce antibodies. They arise within days and weeks from specialized blood cells. Immunologist Carsten Watzl calls the antibodies an “army” that must grow as quickly as possible through cell division. If the real pathogen invades the body again, be prepared. The antibodies blocked the binding site of the virus, and then it could no longer infect the body’s cells.

Already infected cells are simply destroyed by T cells, also known colloquially as T killer cells. It prevents the disease from spreading throughout the body.

The second important part of the immune response are so-called memory cells. These are found in both the B cells responsible for antibody formation and the T cells. After an infection, the body produces these memory cells that contain information about a pathogen such as SARS-CoV-2. If the infection is re-infected, they can start the immune reaction, produce antibodies and form specific T cells within a day. So the virus can be fought quickly. Researchers suspect that this also seems to be the case with SARS-CoV-2. They were able to show that those who have recovered form memory T cells that remain in the body for a long time.

How are the disease processes?

Vaccinated people have a clear advantage – even in the event of an infection. Because on average they were no longer as sick, explains the immunologist O’Brien. Many are unlikely to notice an infection or develop only mild symptoms.

But here too, not all age groups are equally affected: In a study by the Yale School of Medicine in the USA, the data of almost 1000 Covid patients were analyzed. The group of people who became seriously ill despite being vaccinated and had to be treated in hospital was 80.5 years old on average. Many had previous chronic illnesses.

How good is the protection against a severe course?

Nevertheless, the following applies to older people: Overall, the vaccination continues to provide good protection against a serious or fatal course. The effectiveness of the vaccinations in the older group declines over time – but when it comes to preventing severe courses, according to current Israeli data, protection is over 80 percent in all age groups.

According to the Robert Koch Institute, with a full vaccination in Germany, around 85 percent of people over the age of 60 are still protected from hospitalization, 90 percent from treatment in the intensive care unit and around 87 percent from a fatal course. These numbers relate to reported vaccination breakthroughs over the past four weeks.


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