This year, World Immunisation Week runs from 24-30 April and highlights the importance of vaccinating young children against diseases.
Across the UK, vaccination levels have fallen in recent years, with an estimated three million children and young people missing out on their measles, mumps and rubella vaccinations (MMR), according to the National Institute for Clinical Health and Excellence (NICE).
Vaccines work by producing antibodies to fight the disease without actually infecting a person with the disease. If a vaccinated person comes into contact with the disease itself, their immune system will recognise it and immediately produce antibodies to stop them from becoming infected.
Children who have not been vaccinated are at risk of catching diseases that can be easily prevented, and they can also put their schoolmates at risk - especially those who cannot receive certain vaccines for medical reasons.
Dr Adrian McLachlan, Chair of Lambeth Clinical Commissioning Group said: "It is important that parents understand the benefits of vaccinating their children. When they get vaccinated against a certain disease, they build up their immunity, making them stronger and more resistant to that disease."
"Throughout the school year, children are exposed to many serious childhood diseases and vaccines protect them from these. Vaccines are the most effective way in preventing deadly viruses such as measles, mumps and rubella in the population too. That's why it's important to keep your family up to date with the recommended vaccines."
Vaccines are thoroughly tested before they are made routinely available. They are also continually monitored, even after they have been introduced to make sure they continue to be safe.
If you have any concerns about vaccinations talk to your GP, or visit NHS Choices for further information.
This includes a useful checklist of the vaccines that are routinely offered free of charge to everyone in the UK. You can also find information on travel vaccinations.