What is the difference between the vaccines made by Pfizer/BioNTech, Moderna, and AstraZeneca?
Prof. Susanna Zierler: With the help of the so-called spike protein, the SARS-CoV-2 virus attaches to a specific surface protein on certain body cells. The spike protein also helps the virus be absorbed by the cell, resulting in body cells becoming infected. The new vaccines aim to prevent this by targeting this spike protein in particular.

The vaccines made by both Pfizer/BioNTech and Moderna are fairly similar mRNA vaccines and differ just a little. Encapsulated in small lipid beads, the mRNA contains the blueprint for the SARS-CoV-2 virus spike protein. The lipid particles act as a transport system to introduce the mRNA into the cell. The cell then begins to produce the spike protein itself.

The AstraZeneca vaccine, on the other hand, uses a so-called virus vector as a transport system. Based on a weaker cold virus that cannot really cause an infection, this is basically a kind of “viral envelope” that has had its own genetic material removed and replaced with the spike protein. This principle was used successfully in an Ebola vaccine that has been approved since 2019.

There are currently over 60 potential vaccines in clinical trials and around 170 others in pre-clinical development. The European Medicines Agency (EMA) recently approved AstraZeneca's vaccine. Prior to this, the two mRNA vaccines made by Pfizer/BioNTech and Moderna had already passed the approval procedure. There is hope that others will soon follow.

What does a vaccine do in the body?
Prof. Susanna Zierler: As already mentioned, most vaccines use the SARS-CoV-2 virus’ spike protein as a defining feature. This means that this protein is presented to the immune system in order to prepare it to protect the body from infection by the virus. The new mRNA vaccines stimulate the cell to produce the spike protein for the short term. Cells in the innate immune system then basically serve this up on their surface as if on platters. Eventually, the cells recognize this as 'foreign' and the acquired immune system, the T-helper cells, and will then activate these key cells to direct further immune response. These T-helper cells also stimulate the production of protective antibodies by additional immune cells (B-cells). These activated T-cells and B-cells eventually create so-called memory cells that can respond immediately in the event of a new viral infection. The body has a higher level of protection on a cellular level to prevent an outbreak of the disease or the reaction may not be as severe.

How can pharmacologists exclude the possibility of undetected effects / long-term consequences due to the vaccines’ rapid development?
Prof. Susanna Zierler: Unfortunately, unknown long-term effects can never be ruled out with certainty, but this has nothing to do with the vaccines’ rapid development to combat the SARS-CoV-2 virus. Only those factors studied during the clinical trials can be determined with certainty. The study process is currently faster than normal, but the number of subjects and the conduct are in line with a norm that has very high standards in Europe. Ultimately, the decision to be for or against vaccination is based on a clear risk assessment. When it comes to Covid-19 risk groups, such as older people and people who have pre-existing medical conditions, the benefit is clearly paramount. However, the vaccination could also benefit the rest of the population and protect recipients from experiencing the illness severely as well as indirectly protecting family and friends.

What are potential side effects?
Prof. Susanna Zierler: The newly approved vaccines’ spectrum of side effects is similar to those of conventional vaccines, ranging from redness and pain at the injection site, headaches and joint pain to fever and chills. These side effects are probably more common after the second dose, but usually last only one day. More dangerous, but also extremely rare, are allergic reactions up to allergic shock. Patients who have a history of increased risk of allergic reactions must be monitored for several minutes after being immunized.

Are there groups of people who have pre-existing conditions that should not be vaccinated?
Prof. Susanna Zierler: As with any vaccine, people who feel ill should not be vaccinated. Immunocompromised patients and pregnant women were not included in the clinical trials. For safety reasons, there is no clear recommendation to vaccinate pregnant women at this time. However, there is evidence from participants who became pregnant during the trials and there was no indication of any direct or indirect harm. For immunocompromised individuals in particular, an mRNA-based vaccine, similar to a dead vaccine (killed pathogen), might be preferable to a conventional live vaccine (weakened pathogen). The mRNA cannot replicate in the body and cannot cause illness. However, the protective immune response may be somewhat weaker in immunocompromised patients. More tests and studies are needed to determine whether or not there is sufficient protection.

Why should children not be given the vaccine? Why is it difficult to develop vaccines for children?
Prof. Susanna Zierler: Children have not been a part of the conducted and ongoing studies. It is more common to test new vaccines in adults first and then, once approved, consider a gradual extension to children. However, since children have a less severe reaction to the disease, older persons and those in high-risk groups are the priority at the moment.

What does herd immunity mean?
Prof. Susanna Zierler: If there is a high rate of those vaccinated in the population, a pathogen can no longer be easily transmitted from person to person and the disease cannot spread. After some time, the disease then disappears completely, and that, of course, would be the stated goal. The point in which this kind of "herd immunity" exists varies from disease to disease. Looking at measles, for example, we can attain this effect once the vaccination coverage rate is around 95%. We don’t know how high the vaccination rate for Covid-19 has to be in order to achieve this kind of herd immunity. Up until now, we assumed it’s a rate of 60-70%. However, the new SARS-CoV-2 virus mutations seems to be much more transmissible so currently, experts believe the coverage rate needs to be more around 80-85%.

How long does Covid-19 vaccine immunity last?
Prof. Susanna Zierler: Unfortunately, at the moment we cannot say for sure. However, we expect will take several months to years. This also depends, of course, on how much the virus continues to mutate. If existing vaccines provide less sufficient protection when it comes to virus mutations, the new mRNA vaccines can be used for a quicker response. We just need to modify the mRNA blueprint accordingly.

Will you be getting vaccinated? If yes: which of the vaccines do you prefer?
Prof. Susanna Zierler: Definitely! As soon as it is my turn, I will gladly take the vaccine intended for me. I not only have confidence in the science, but also in the clinical studies and the regulations in effect to approve drugs at the European Medicines Agency.