How falling measles vaccination rates put millions of children at risk

As measles vaccination rates drop and zero-dose children rise, a new study urges urgent action to prevent a resurgence of this deadly disease.

Study: Measles Vaccination Coverage and Anti-Measles Herd Immunity Levels in the World and WHO Regions Worsened from 2019 to 2023. Image Credit: Phichet Chaiyabin / Shutterstock

In a recent study published in the journal Vaccines, researcher Pedro Plans-Rubió at the College of Physicians of Barcelona assessed zero-, one-, and two-dose vaccination coverage across 2030 across all World Health Organization (WHO) regions. They compared data from WHO and the United Nations Children’s Fund (UNICEF) databases between 2019 and 2023 to evaluate if current immunization coverage is on track to meet Immunization Agenda 2030 (IA2030) objectives.

Study findings revealed several alarming trends: 1. Global two-dose vaccination coverage in 2023 decreased by 3.7% compared with 2019 levels; 2. One-dose vaccination coverage improved by 7.8% globally, but most measles vaccination coverage indicators depict lower values than those from 2019; and 3. Current vaccination coverage is not on track to achieve IA2030 agreements. These findings highlight a need for policy and public health implementations to increase two-dose vaccination globally.

Additionally, the study found that zero-dose measles vaccination coverage — indicating children who received no doses — increased by 7.8% globally between 2019 and 2023, with a particularly concerning 24.9% rise in the African region. As of 2023, the number of zero-dose measles children was 40.6% higher than the level needed to remain on track for halving zero-dose children by 2030, a key IA2030 target.

Background

Measles, sometimes called ‘rubeola,’ is a highly contagious airborne viral infection resulting in high fever, cough, red eyes, and rashes. It often afflicts children and was once lethal, though advances in clinical interventions have since diminished its severity.

Measles is an eradicable disease. Medical science has developed effective vaccines against the exclusively human-borne measles virus (genus Morbillivirus), which, alongside intensive epidemiological surveillance, can curb its infectivity and halt its transmission. In light of this, the 73rd World Health Assembly’s Immunization Agenda 2030 (IA2030) committed to eliminating the disease from at least five World Health Organization (WHO) regions (out of six total regions) by 2030.

To achieve this agenda and effectively immunize individuals, two doses of vaccination (measles-containing vaccine [MCV]) are required. The WHO has implemented the widespread dissemination of the measles–mumps–rubella (MMR) vaccine alongside education about its administration to children between the ages of 12 and 15 months (first dose) and again between 3 and 15 years (second dose).

“High percentages of routine measles vaccination can generate both individual measles protection and sufficient population herd immunity to block measles transmission in the community.”

Unfortunately, 2019 research aimed at tracking global progress toward IA2030 goals demonstrates that only 14.4% of countries had two-dose vaccination coverage ≥ 95%. Worryingly, the basic reproduction numbers (R0) of African and Eastern Mediterranean regions were found to be ≥ 10, ≥ 11 in Western Pacific regions, and ≥ 13 in European, American, and South-East Asia regions. These R0 values correspond to required population immunity levels ranging from 90% (for R0 = 10) to 95% (for R0 = 20), and R0 is a metric that denotes the number of clinical cases a single infection within a community can trigger.

About the study

The present study aims to update this information by assessing: 1. The 2023 global measles vaccination coverage in WHO member nations (zero-, one-, and two-dose coverage); 2. Comparing current variations in measles vaccination coverage to 2019 levels; and 3. Assessing whether measles vaccination indicators are on track to meet IA2030 goals.

Study data was obtained from the WHO and the United Nations Children’s Fund (UNICEF) databases (global and regional). This data is recorded annually in all WHO member nations across its six designated regions: Africa, the Americas, the Eastern Mediterranean, Europe, Southeast Asia, and the Western Pacific.

For estimating anti-measles herd immunity levels and similar measles vaccination indicators, this study assumed that one vaccination dose provided 92% immunity to individuals, while two doses imparted 95% immunity. Correspondingly, required immunity percentages were calculated based on R0 thresholds — for example, 93.3% population immunity is needed to block measles viruses with an R0 of 15.

“…tracks required from 2019 to 2030 to achieve a 50% reduction by 2030 were determined for three zero-dose measles coverage indicators: (1) estimated number of children who did not receive the first dose of measles-containing vaccine (MCV1); (2) mean MCV1-based zero dose coverage; and (3) mean zero dose coverage determined from one and two doses of measles vaccine coverage.”

All statistical analyses were carried out in Microsoft Excel.

The number of zero-dose measles children (who did not receive the MCV1 vaccine) is estimated from 2019 and 2023, and a number of zero-dose children required from 2019 to 2030 to achieve the IA 2030 objective (9.65 million).

Study findings

Analyses results revealed that, on average, only 85.2% and 77.1% of WHO region children had received one or two doses of MCV vaccine, respectively. This corresponds to a 3.7% reduction in two-dose vaccination coverage compared to 2019 and is significantly below the on-track estimates for meeting IA2030 targets. Notably, only the Western Pacific region met MCV two-dose requirements of 95.5%, while the European region reached 92.5% coverage and all other regions were below 95%.

Dose-specific findings revealed that global zero-dose coverage was 65.3%, one-dose at 27.8%, and two-dose at 6.9%, with Africa’s zero-dose rate at 21.1% — far higher than other regions (less than 3%). These rates are more than 31% lower than IA2030 requirements. The African region demonstrated the lowest one-dose coverage, with 48.1%, while the Western Pacific region had the highest coverage (93.2%). Only 17 WHO member nations (8.7%) were found to have two-dose vaccination coverage of 95% or above.

Regarding herd immunity, the study found that only 41.5% of countries achieved sufficient immunity to stop measles virus transmission with R0 values of 15 or lower, and no region achieved immunity sufficient to block viruses with R0 ≥ 19 or 20. Only the Western Pacific region and some countries in the European region reached levels to prevent community-level outbreaks of highly contagious strains (R0 ≥ 15).

Despite some regional variations—the Western Pacific region has shown modest improvements since 2019—most areas, especially Africa, showed deteriorations in vaccination coverage and herd immunity levels.

The study noted that these trends were compounded by disruptions from the COVID-19 pandemic, which significantly impacted routine immunization programs and delayed recovery efforts.

In addition, the paper highlighted limitations such as reliance on WHO/UNICEF data, which may underrepresent gaps in certain populations, and emphasized the need for serological surveys to assess real-world immunity.

Conclusions

The present study highlights the decrease in the effectiveness of WHO-endorsed anti-measles vaccination programs in its six regions between 2019 and 2023 (-3.7% for two-dose coverage), with only one region (Western Pacific) depicting improvements from 2019 findings. While one-dose coverage increased by 7.8% globally, all metrics of measles vaccination coverage indicate that current efforts are not on track to meet IA2030 goals.

This underscores the need for policy improvements and enhanced vaccination dissemination programs aimed at both education and successful two-dose vaccine administration to help eradicate this childhood disease from the human population.

The study also calls for broader international cooperation and targeted efforts in regions like Africa to close immunization gaps and build sustainable herd immunity.