Why the COVID-19 vaccines are safe

Vaccination is a simple, safe, and effective way of protecting people against harmful diseases before they come into contact with them. It uses your body’s natural defenses to build resistance to specific infections and makes your immune system stronger. During the COVID-19 pandemic, vaccination continues to be critically important. When you get a vaccine, your immune system responds. The vaccine is therefore a safe and clever way to produce an immune response in the body, without causing illness. Vaccines are getting ready before a battle; your opposition is kept at bay.

Herd immunity, also known as ‘population immunity’, is the indirect protection from an infectious disease that happens when immunity develops in a population either through vaccination or through a previous infection. The World Health Organisation (WHO) supports achieving ‘herd immunity’ through vaccination, not by allowing the disease to spread through a population, as this would result in unnecessary cases and deaths.

Two key reasons to get vaccinated are to protect ourselves and to protect those around us. Because not everyone can be vaccinated including very young babies, those who are seriously ill or have certain allergies, depend on others being vaccinated to ensure they are also safe from vaccine-preventable diseases. An experimental vaccine is first tested in animals to evaluate its safety and potential to prevent disease. It is then tested in human clinical trials, in three phases.

In phase I, the vaccine is given to a small number of volunteers to assess its safety, confirm it generates an immune response, and determine the right dosage.

In phase II, the vaccine is usually given to hundreds of volunteers, who are closely monitored for any side effects, to further assess its ability to generate an immune response. In this phase, data are also collected whenever possible on disease outcomes, but usually not in large enough numbers to have a clear picture of the effect of the vaccine on the disease. Participants in this phase have the same characteristics as the people for whom the vaccine is intended. In this phase, some volunteers receive the vaccine and others do not, which allows comparisons to be made and conclusions are drawn about the vaccine.

In phase III, the vaccine is given to thousands of volunteers some of whom receive the investigational vaccine, and some of whom do not, just like in phase II trials. Data from both groups are carefully compared to see if the vaccine is safe and effective against the disease it is designed to protect against. Almost all the COVID-19 vaccines have gone through all the phases of a trial.