The vaccination against corona should start soon. Manufacturers have already submitted approval applications for two preparations in the EU, and approval could be granted within weeks.
Given the rapid pace of development in vaccines, however, some people get a queasy feeling. Are These Vaccines Really Safe? Have potential side effects been studied well enough? Isn’t it perhaps more sensible to accept a corona infection than to expose yourself to the risks of a new vaccine?
These questions are certainly not unjustified. Especially since the two vaccine candidates – one from the US company Moderna and one from the Mainz company Biontech in cooperation with the US pharmaceutical giant Pfizer – are so-called mRNA vaccines, which are based on a still new vaccine technology.
So far there is not a single approved vaccine in the world that is manufactured and works in this way. The fundamental difference between these novel vaccines and established vaccines: They do not contain any weakened or killed viruses, but only instructions for a component of the Covid-19 pathogen. The instructions are inoculated into the body in the form of a so-called mRNA molecule, where the human cells then produce a protein of the virus themselves. In the case of Sars-CoV-2, it is the so-called spike protein on the surface of the virus. It stimulates the human immune system to produce antibodies.
Initial data from the advanced clinical trial suggest that the vaccines are highly effective and generally well tolerated. According to the company, some of the vaccinated test persons experienced fatigue, headache and joint pain and redness at the injection site as side effects. Similar reactions are known from other vaccines and are also a sign that the vaccine is doing what it is supposed to: get the immune system going.
What is missing so far is information on rare, possibly severe side effects, as these only become apparent after vaccination of many people and a longer observation period. “There is therefore a residual risk,” says Christian Bogdan, Director of the Institute for Clinical Microbiology, Immunology and Hygiene at the Erlangen University Hospital. “How high that is will have to be checked in the coming months and years.” In order to record rare side effects, it is common practice to continue clinical studies even after approval.
Basically, the decision for or against a vaccination is always based on a risk-benefit analysis, says the expert, who is also a member of the Standing Vaccination Commission (STIKO) at the Robert Koch Institute (RKI). He makes the following example calculation: If an old person dies with a corona infection with a probability of 20 percent, “and at the same time the risk of getting a serious side effect of the vaccination is 1:50,000 or even less, I would take this risk accept. ”
Bogdan, on the other hand, would not vaccinate children because their risk of dying from Covid-19 is almost zero and at the same time they still have a very long life ahead of them. “These are all completely legitimate ethical considerations,” emphasizes Bogdan. They are also reflected in the vaccination recommendations of the Stiko, according to which initially only risk groups should be vaccinated. “In this way we achieve what we want: achieve the greatest possible benefit for society as a whole.”
But aren’t the risk groups in particular – elderly people or those with a previous illness – exposed to particular dangers when vaccinated? All risks cannot be ruled out at this stage in vaccine development, says Ulrike Protzer, director of the Institute for Virology at the Technical University of Munich (TUM) and at the Helmholtz Zentrum München. However, some special patient groups have already been taken into account in the clinical studies.
The company Moderna, for example, also tested its vaccine on people over 65 years of age, those with diabetes, severely overweight or heart disease. According to the company, no security concerns have arisen. “The risk of a rare, serious side effect is not nil, but compared to other risks that we accept every day, such as when driving a car, it is very low,” says Protzer.
Experts consider concerns that mRNA vaccines in particular pose particular safety risks and, for example, alter the human genome to be unfounded. “In humans, the genome is in the form of DNA in the cell nucleus,” says the Paul Ehrlich Institute, which is responsible for the safety of vaccines. “Integration of RNA in DNA is not possible due to the different chemical structure, among other things.”
A special feature of RNA is that it is chemically very labile. “When the mRNA gets into the cells, it is broken down again very quickly,” explains Protzer. A sustainable interaction with the human cell is unlikely for this reason alone. To increase the shelf life, the vaccine mRNA is packed in a kind of protective cover. “We have to observe what these additives do,” says Protzer. “One assumes a good tolerance, but there is still a lack of long-term experience.”
With a view to the safety of mRNA vaccines, another point is important: Although none of these vaccines have been approved for humans so far, the technology was not only developed in the wake of the corona pandemic; some experience with it is already available. The idea for this type of vaccine comes from basic immunological and infectiological research and from cancer research. The aim is to induce the body to attack tumor cells; clinical studies are already underway in this area. “The pandemic has now given the technology a huge boost,” says Bogdan.
The new mRNA vaccines have another special feature. Unlike weakened and killed viruses, which stimulate the immune system with many different surface structures, the mRNA vaccines trigger a very specific immune response. This can be an advantage because it may prevent unwanted reactions. On the other hand, there is a risk that this very specific immune response will not provide adequate protection.
It is also unclear what happens if the coronavirus mutates, i.e. if the pathogen’s spike protein changes – does the vaccine still work? In order to be able to answer these questions with certainty, a longer follow-up period is required. “But this is not a new challenge for vaccine research.”