The world's population is rapidly ageing. For the first time in history, adults over 65 now outnumber children under five. By 2030, nearly 1 billion people will be in this age group.
Yet, while childhood immunization programmes have saved millions of lives, vaccination of adults remains an overlooked tool—especially in low- and middle-income countries, where efforts have historically focused on reaching children, adolescents, and women of reproductive age.
A recent World Health Organization (WHO) study published in Vaccines underscores the value of adult vaccination to achieve healthy aging, while meeting the challenge of rising healthcare costs and antimicrobial resistance.
Although WHO recommends vaccines against diseases such as influenza, COVID-19, pneumococcal disease, tetanus, and respiratory syncytial virus (RSV), among others, for different adult population groups, the study finds that access remains unequal. Many low- and middle-income countries have yet to include vaccines targeting adults in their national schedules—leaving millions unprotected.
"As outbreaks of vaccine-preventable diseases increase, it's more critical than ever that people receive every recommended dose—through every stage of life—to stay protected," said Dr Alba Vilajeliu, lead author and technical officer in the Department of Immunization, Vaccines and Biologicals at WHO. "This isn't just about saving lives; it's also about increasing the quality of life for adults, their productivity within communities and alleviating the burden on already overstretched health systems."
Under Immunization Agenda 2030, a global strategy for vaccination, countries envision a world where everyone, everywhere, at every age benefits from vaccines. Expanding adult immunization programmes will not only benefit older populations it will strengthen immunization programmes across the life course by enhancing health worker capacity, infrastructure and confidence in vaccines.
Adult immunization can be scaled quickly – as shown by COVID-19
The COVID-19 pandemic thrust adult vaccination into the global spotlight, driving major shifts in policies, attitudes, and health systems traditionally focused on childhood immunization. By the end of 2023, more than 13.6 billion COVID-19 vaccine doses had been administered globally, reaching 89% of health workers and 84% of older adults.
However, the WHO-study found those efforts have yet to translate to other adult vaccines. Despite seasonal influenza causing 3 to 5 million severe cases and up to 650 000 deaths annually, just 4% of low-income countries offer influenza vaccines to pregnant women, and only 8% to older adults. In contrast, high-income countries include them in 87% and 89% of national immunization schedules for these groups, respectively.
More than 50 years ago, countries began providing tetanus-containing vaccines for pregnant women to prevent maternal and neonatal tetanus. Today, 73% of low-income and 80% of lower-middle-income countries offer these vaccines. The experience of these and other vaccines for pregnant women offers valuable lessons for introducing new ones, like the maternal RSV vaccine to protect infants or future vaccines to prevent Group B streptococcus and malaria in pregnancy.
A recent Office of Health Economics (OHE) report also found that scaling up adult vaccination programmes for seasonal influenza, RSV, herpes zoster and pneumococcal disease in just 10 high- and upper middle-income countries returned up to 19 times their initial investment, offering a potential greater return in low- and middle-income countries. This amounted to up to US$ 4637 per individual full vaccination course.
New vaccines and innovations will broaden adult immunization
In addition to scaling up existing adult vaccines, new vaccines in development—like the next generation of tuberculosis vaccines, and vaccines for combinations of respiratory viruses—are expanding target groups beyond childhood. Through new platform technologies, such as mRNA, vaccine candidates are advancing into clinical testing at faster rates, without compromising safety.
Countries will need to continue to strengthen immunization programmes as part of primary health care services in order to introduce new- and under-utilized adult vaccines, scale-up existing vaccines, and ensure strong demand and uptake for adult immunization. Additionally, health workers will need to be trained to communicate on the importance of immunization across the life course. Engaging community leaders and healthcare professional networks will be essential for developing tailored communication for adult populations.
"As vaccination expands across the life course, now is the moment for countries to lay a strong foundation," says Dr Kate O'Brien, Director of the Department of Immunization, Vaccines and Biologicals at WHO. "When we prioritize disease prevention to support lifelong health, we create continuous opportunities for health and well-being—and shift from a disease-centered model to one that truly puts people first. Adult immunization is central to that shift."
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