Adverse event following immunization is any untoward medical occurrence which follows immunization and which does not necessarily have a causal relationship with the usage of the vaccine. If not rapidly and effectively dealt with, can undermine confidence in a vaccine and ultimately have dramatic consequences for immunization coverage and disease incidence. Alternatively, vaccine-associated adverse events may affect healthy individuals and should be promptly identified to allow additional research and appropriate action to take place.

There is no such thing as a “perfect” vaccine which protects everyone who receives it and is entirely safe for everyone. Effective vaccines (i.e. vaccines inducing protective immunity) may produce some undesirable side effects which are mostly mild and clear up quickly. The majority of events thought to be related to the administration of a vaccine are actually not due to the vaccine itself – many are simply coincidental events, others (particularly in developing countries) are due to human, or programme, error.

BioTalk on Adverse Effect Following Immunisation

It is not possible to predict every individual who might have a mild or serious reaction to a vaccine, although there are a few contraindications to some vaccines. By following contraindications the risk of serious adverse effects can be minimized. Effective spontaneous reporting of adverse events following immunization (AEFI) is the first step to making sure that vaccine products are safe and are being safely administered. Yet almost half the world’s population lives in countries without an effective system for monitoring the safety of vaccines.

Severe reactions following immunization are extremely rare so several countries have joined forces to pool their AEFI data in a common global database. The database is managed by the WHO Programme for International Drug Monitoring. Experience shows that most severe AEFI are not true vaccine reactions; rather, they are coincidental occurrences of health events or the anxiety associated with receipt of a vaccine. The goal is that all countries should at least have a system for spontaneous reporting of AEFI and for investigating those that are serious. Countries that manufacture vaccines and countries where newly available vaccines are being introduced should have additional capacity for vaccine pharmacovigilance.

girl getting vaccinated
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Block rejection, lower immunization uptake, loss of confidence in RI, attack on RI providers, discrimination of RI providers, and divorce threats among spouses were the consequences and crises the healthcare providers mentioned due to AEFI. Proactive and reactive communication with the caregivers and community members would minimize the consequences of AEFI. In line with the guideline, the respondents in our study explained that health education of the caregivers, community sensitization, and community dialogues were strategies adopted to overcome AEFI consequences.

The most obvious findings that emerged from studies are the varying understanding of AEFI definition and classification among RI providers. Among different possible causes of AEFI, error during vaccination was frequently mentioned by the study participants. Low uptake of immunization due to AEFI was one of the consequences of AEFI at the community level. Educating caregivers, community sensitization and community dialogue were actions taken by the respondents to overcome the consequences of AEFI. Besides, refresher training on safe injection procedures and symptomatic treatment of AEFI were ways to prevent AEFI and its negative consequences.

The Nigerian AEFI surveillance guideline broadly categorized AEFI based on causes, seriousness and frequency. Cause-specific types of AEFI are classified as vaccine product-related reaction, vaccine quality defect-related reaction, immunization error-related reaction, immunization anxiety-related reaction and coincidental events. Vaccine reactions by seriousness and frequency are classified as non-serious reactions and serious reactions.

Careful investigation of all serious AEFIs is critical. The ultimate goal of an investigation is to determine the likelihood of a causal link between a reported AEFI and the vaccine(s) administered or the vaccination process, or alternately to find another cause. The findings of the investigation should lead to appropriate action, where needed, to prevent further AEFIs. Effective and efficient management of AEFIs is an essential component of all immunization programmes in order to ensure continued public confidence in vaccination, and ultimately to ensure high immunization coverage and thereby reduction in disease and death due to vaccine-preventable diseases.

WHO, at the request of governments of Member States, provides assistance to national authorities for the investigation of serious AEFIs. In particular, WHO works with national authorities to ensure appropriate investigation and response to serious AEFIs reported following the administration of WHO-prequalified vaccines.


World Health Organisation (2023) Adverse Events Following Immunization (AEFI)

Omoleke, S. A., Getachew, B., Isyaku, A., Aliyu, A. B., Mustapha, A. M., Dansanda, S. M., Kanmodi, K. K., Abubakar, H., Lawal, Z. I., & Kangiwa, H. A. (2022). Understanding and experience of adverse event following immunization (AEFI) and its consequences among healthcare providers in Kebbi State, Nigeria: a qualitative study. BMC health services research, 22(1), 741.

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