Childhood vaccine coverage not yet back to pre-pandemics levels: WHO, UNICEF

The number of people globally who have received certain vaccines has still not returned to pre-pandemic levels, according to a new joint report of estimates from the World Health Organization (WHO) and the United Nations Children's Fund (UNICEF).

Estimates of coverage of the first dose of the diphtheria, tetanus and pertussis vaccine (DTP) and the measles-containing vaccine (MCV) remained stable from 2022 to 2023 – higher than rates during the pandemic but lower than pre-pandemic estimates, according to the report, which was published on Sunday evening.

Additionally, an estimated 21 million children missed one or more vaccines in 2023, about 2.7 million more than seen in 2019.

"The global immunization coverage has stagnated, or it is stalling," Dr. Ephrem T. Lemango, associate director of immunization at UNICEF, told ABC News. "It's not really recovering as quick as we want."

For the report, WHO and UNICEF researchers reviewed vaccination coverage data submitted from more than 190 countries and performed analyses, with consideration of potential biases and local expert opinion, to produce global and country-specific estimates.

One of the major findings of the report was that, for estimates of when infants received the first dose of the DTP vaccine, 89% of infants did so in 2023, which is the same percentage as in 2022. However, this year's percentage is lower than the 90% of infants in 2019 who received the first dose, the report found.

Estimated coverage for the third dose of the DTP vaccine also remained unchanged at 84% from 2022 to 2023, but lower than the 86% in 2019 who received all three doses of the vaccine.

Lemango said although DTP coverage is stalling, it is nonetheless approaching pre-pandemic levels and is higher than coverage seen during the pandemic.

"We can safely say that, even though it feels very slow, we are on a path to recovery, which is basically going back to pre-pandemic levels," he said.

Additionally, the number of children of who were unvaccinated against DTP increased from an estimated 13.9 million in 2022 to 14.5 million in 2023. Nigeria had the highest absolute number of children who had not received a single dose of the DTP vaccine during that time, followed by India, according to the report.

The report also found that not all children who began their vaccine schedule finished it. In 2023, an estimated 6.5 million children globally did not complete their follow-up doses of the DTP vaccine, which is higher than the 5.5 million children that missed follow up doses in 2019.

The report also looked at coverage of the MCV vaccine, which protects against measles. Lemango explained that measles is a highly contagious disease and, because it spreads so quickly, it acts as a "canary in the coalmine," revealing potential gaps in immunity coverage.

"So, if you see measles outbreaks increasing across countries, it shows you these are the areas where there is an immunity gap and, if you can identify these areas, you will usually also end up realizing these children are also not getting other vaccines, and, most likely, they are not even getting other health services," he said.

The first dose of MCV is recommended at 9 months old in countries with ongoing transmission of measles, and at 12 months old in countries with low risk of transmission, according to a WHO-funded study.

Similar to DTP, the estimated percentage of children who received the first dose of MCV was unchanged from 2022 to 2023, at 83%, lower than the 86% in 2019 who received a first dose.

Additionally, an estimated 22.2 million children in 2023 missed their routine first dose of measles vaccine, according to the report.

However, there were some positive signs in the report. In 2023, coverage of the first dose of the human papillomavirus (HPV) vaccine among females increased from 20% in 2022 to 27% in 2023, while coverage of the last dose increased from under 15% in 2022 to 20% in 2023.

HPV has been linked to numerous cancers, including head and neck, throat, penile, cervical and rectal cancer. Receiving the HPV vaccine has been shown to prevent cancers caused by the virus, according to the Centers for Disease Control and Prevention.

To drive increased vaccine coverage, Lemango said organizations need to make sure vaccine delivery service continues even during conflicts, which is one of the major drivers of missing vaccinations. Countries also need to ensure they're keeping their vaccine stockpiles supplied, he said.

Lastly, Lemango said organizations need to continue to improve and maintain vaccine confidence.

"In so many places, vaccine confidence – such as mistrust in the system, mistrust in the vaccines and mistrust in the people who deliver these vaccines – tends to affect the overall uptake of any vaccine," he said. "So, we need to make sure that we build systems that are able to be trusted by the community. As workers, we need to continue to provide the right and complete information to parents."