Before a vaccine is approved for public use, it undergoes thorough testing. Similar to other medications, vaccines are subjected to detailed clinical trials, where they are given to and carefully observed in groups of volunteers. In the UK, the Medicines and Healthcare products Regulatory Agency (MHRA) reviews the trial outcomes to ensure safety and efficacy.

No medication, including vaccines, can be entirely free of risk or guaranteed to work 100% of the time. However, robust approval processes and safety evaluations confirm that the health benefits of vaccines provided through the NHS far exceed any potential risks. Because vaccines are administered to healthy individuals, the safety standards are exceptionally high, setting a lower threshold for acceptable risk compared to other drugs.

Even after a vaccine is included in the routine schedule, the MHRA continues to monitor its safety and effectiveness. Any potential side effects can be reported by healthcare professionals or patients to the MHRA via the yellow card scheme.