How do vaccines work?

The purpose of a vaccine is to help develop immunity to an infectious agent by stimulating the immune system to produce antibodies, thus protecting against future infections.
In the case of the new coronavirus, a vaccine can make the vaccinated person less susceptible to an infection with the virus and thus the COVID-19 disease it causes. At the very least, it should make an infected person have a shorter duration of illness or fewer complications.

Why should I get vaccinated even if I am not part of the vulnerable or elderly population?

Given the current epidemiological situation, it is important to primarily ensure a protection for those who are most at risk. This includes people over 65 years of age or those who are vulnerable, particularly because of an underlying disease that increases the risk of complications or death. People at high risk to develop a severe course can be found in all age groups due the individual health condition.

However, also people not belonging to these categories can transmit the virus once they are infected, even if they might not show any or only light symptoms. The vaccination is expected to reduce the transmission of the virus and thus is an act of solidarity: When you get vaccinated, you can also help to protect everybody around you.

I had a COVID-19 infection in the past and recovered. Do I still need to get vaccinated?

Yes. At the current state, there is no data available for how long someone is protected from getting COVID-19 again after infection. Early evidence suggests that natural immunity from COVID-19 may last for around 5 months, but more studies are needed to better understand this.

Therefore, it is highly recommended to get vaccinated even if you have had COVID-19 in the past. Also, there have been no reports of safety problems associated with vaccinating individuals with a history of COVID-19 infection, or with detectable COVID-19 antibodies.

How can I be sure that the vaccines are safe?

All COVID-19 vaccines are being developed following the same legal requirements as other types of drugs. Like for all medications, effects of COVID-19 vaccines are first tested in laboratories (cells and animal models), then, in a later phase, they are tested in human volunteers. There are several stages of human testing which are referred to as phases of clinical trials. At each stage, they have to pass many tests to enter into the next phase until they finally can get approved by the European Medicine Agency:

Pre-clinical testing:
The developed vaccine is tested in the laboratory using cell cultures or animal models. Efficacy, toxicity and pharmacokinetics are addressed at this point. No testing on humans is performed until the preclinical testing is completed.

Clinical testing - Phase 1:
Healthy volunteers are recruited to test the safety of the drug. Different doses are tested, and the possible dosage of the vaccine is assessed. Adverse effects are very closely monitored in this stage.

Clinical testing - Phase 2:
Volunteering patients (usually several hundreds) are recruited to test the efficacy of the drug. Side effects are closely observed with regards to the mechanism of action of the vaccine.

Clinical testing - Phase 3:
Several hundreds to several thousands of volunteering patients are participating in two groups. One group will receive the new vaccine whereas the other group receives the standard-of-care treatment or a placebo if there is no alternative vaccine available. Only if the tested vaccine has proven a significant improvement in treatment and passes all safety criteria, approval by the authorities can be given.

Clinical testing - Phase 4:
This phase is conducted after approval of the vaccine during the subsequent years. The occurrence of rare side effects is monitored. It should be noted that vaccines are generally not expected to have any long-term effects.