Monitoring Vaccine Safety Worldwide, 2020–2022: WHO's New Indicator

Strong safety monitoring after a vaccine is authorized or licensed helps make sure its benefits keep outweighing its risks. Over the past decade most countries built at least basic systems for tracking adverse events following immunization (AEFIs). This CDC and WHO report describes progress from 2020 to 2022.

Two measures

• The old indicator. In December 2014, WHO set its first measure of minimal vaccine safety surveillance: aggregate reporting of more than 10 AEFIs per 100,000 surviving infants. In 2019, 121 of 214 WHO countries and territories (57%) met it.
• The new indicator. WHO's Vaccine Safety Blueprint 2.0 called for more comprehensive measures, and in December 2020 WHO's Global Advisory Committee for Vaccine Safety recommended a new, case-based one covering all ages: at least one serious AEFI reported per 1 million people a year. An AEFI counts as serious if it results in death, is life-threatening, requires or prolongs hospitalization, causes persistent or significant disability, or is a congenital anomaly, among other situations judged serious. Case-based reporting is meant to improve accuracy and help systems detect safety signals — evidence of a possible link between a vaccine and a previously unknown or poorly documented event.

In many countries, surveillance depends on two partners working together: the national regulatory authority (NRA), which makes sure medicines and biologics meet international standards and must monitor safety after authorization, and the national expanded program on immunization (EPI), which buys, stores and delivers vaccines, trains the health workers who give them, and so plays a key role in spotting and reporting adverse events. Coordinated reporting improves data quality so signals are caught quickly.

Data

Countries meeting the new indicator were identified from reports to VigiBase, WHO's global database of individual reports of suspected adverse reactions. Joint reporting was measured from the WHO/UNICEF Joint Reporting Form, which asks whether a country's count of serious adverse events came from the EPI, the NRA, both or another source. Reporting to both is voluntary, and countries that did not report were counted as not meeting either measure. There were 214 WHO countries and territories in 2020 and 2021, and 215 in 2022, when the Pitcairn Islands were added.

Results

WHO countries and territories reporting serious adverse events to VigiBase and meeting the new indicator, 2020–2022. CDC, MMWR.

• By region in 2022, the share meeting the new indicator was highest in Europe (76%), followed by Africa (47%), the Americas (32%), the Eastern Mediterranean (27%) and the Western Pacific (22%), and lowest in South-East Asia (9%).
• Africa saw the largest increase: from 3 countries (6%) in 2020 to 28 (60%) in 2021, before falling to 22 (47%) in 2022.
• Every region except South-East Asia improved from 2020 to 2022, but every region declined from 2021 to 2022.
• Data sources in 2022: of 169 countries that reported a source, 63 relied mainly on the EPI, 33 on the NRA and 57 on both; 17, including the United States (through its Vaccine Adverse Event Reporting System), reported other sources. Joint reporting rose in four regions, fell in the Americas and was unchanged in the Western Pacific.

Primary source of national data on adverse events following immunization, WHO countries and territories, 2022. CDC, MMWR.

What drove the change

The COVID-19 response likely did much of it, bringing more funding, intensive technical support and new monitoring tools such as smartphone apps; most AEFI reports in 2021 involved COVID-19 vaccines, and 2021 was the peak year for meeting the indicator. The dip in 2022 probably reflects smaller vaccination campaigns and less intensive surveillance. Africa and the Eastern Mediterranean made notable gains with WHO support for training, standard tools and national guidelines — yet even in the Eastern Mediterranean, the leader, only half of countries reported jointly, and fewer than half of all countries met the new indicator.

Limitations

The analysis used only VigiBase data, and countries that don't report consistently may be missed; it could not assess how NRA–EPI relationships affect meeting the indicator; and the two measures may not reflect how well a national system actually functions.

Why it matters

Case-based reporting makes adverse event data usable for action — timely detection, investigation, causality assessment by national committees, and response to serious events or clusters. Shared globally, individual reports can reveal trends in rare but serious events that national totals would miss. Continued investment is needed to keep public confidence in vaccination programs.

Sources

• Blau EF, Balakrishnan MR, Sköld H, et al. "Progress in Immunization Safety Monitoring — Worldwide, 2020–2022." MMWR 72(49). CDC.