Although every vaccine goes through three phases of clinical testing before being used, vaccines or vaccine lots (specific batches) can be withdrawn or recalled after being deployed to countries. Vaccine recalls or withdrawals due to safety issues are very rare. Recalls are usually initiated voluntarily by a vaccine manufacturer, if as part of their continuous monitoring of the quality of vaccine production they find an irregularity affecting a specific batch of vaccines. Sometimes, health authorities may temporarily suspend or withdraw a specific vaccine batch as a precaution while they investigate a severe acute event following immunization or a cluster of adverse events. In most cases, a person who had been vaccinated with a vaccine from a recalled batch will not need to do anything after the vaccine is recalled. If the vaccine recall is related to a possible safety concern, people who were vaccinated should talk to their doctor if they have any concerns that they may be having a reaction. If a vaccine recall is due to low vaccine effectiveness, people who were vaccinated with a vaccine from that lot or batch might need to be vaccinated again to ensure they are protected against the disease.