As with any vaccine, it is essential to closely monitor the safety and efficacy of COVID-19 vaccines as they are delivered. If a problem is reported following vaccination, a thorough investigation should take place.

During these investigations, it is extremely rare that health problems are found to be caused by the vaccine itself. Adverse events are most often found to be coincidental and may be entirely unrelated to vaccination. Sometimes they are related to how the vaccine has been stored, transported, or administered. Such errors can be prevented by better training health workers and strengthening supply chains.

In the very rare cases where a genuine adverse reaction is suspected, the vaccine may be suspended from use. Further investigations will take place to determine what exactly caused the event, and corrective measures will be put in place. WHO works with vaccine manufacturers, health officials and other partners to monitor any safety concerns and potential side effects on an ongoing basis.