GENEVA – If you want to know the value of vaccines, just spend some time in a clinic in Africa. The faces of the mothers and fathers say it all: vaccines prevent illness and save lives.But what these parents probably do not realize is that the story does not end there. As they leave the clinic and head home, they have already taken steps to improve not just their child’s health, but also his or her educational prospects and long-term future. What’s more, they will have also helped to improve their own lives and enhance the economic prospects of their wider community.The reasons are simple. We know that children who are healthier do not require medical treatment or care, both of which cost time and money. So, by avoiding illness, infants have a greater chance of growing into healthier children who are able to attend school and become more productive members of society.Meanwhile, instead of caring for a sick child, parents can work, thereby increasing their ability to earn. So, rather than spending money on medical bills, they are boosting their income and spending capacity, both of which help the economy to grow.All of this intuitively makes sense, and there is a growing body of scientific evidence to back it up. It has been shown, for example, that vaccinated children not only do better at school, but also that, through the prevention of damage that can be caused by infectious diseases and resulting nutritional imbalances, they appear to benefit in terms of cognitive development.Similarly, vaccination has been shown to lead to wage gains across populations, while improvements in child survival rates are associated with lower fertility rates. And, in terms of the wider gains, one study found that a five-year improvement in life expectancy can translate into a 0.5-percentage-point increase in annual per capita income growth.What all of this means is that by measuring the effectiveness of vaccines merely in terms of "lives saved,” we could be seriously underestimating the full extent of the benefits that they offer. As things stand, in terms of the cost effectiveness of health interventions, vaccines are already considered one of public policy’s "best buys.”Indeed, it has been calculated that the work being done to expand vaccine coverage in developing countries by my organization, the GAVI Alliance, should yield an 18% return on investment by 2020. But now, as more evidence is gathered, it looks likely that even this may not do justice to the full value of vaccines.Given the progress made in expanding vaccination programs in recent years, this revelation represents a unique opportunity for the global community, particularly as we begin to close the lid on polio. With poliovirus now endemic in just three remaining countries, we are already beginning to use the momentum that has carried eradication efforts so far to broaden the scope of routine immunization to reach more of the poorest children. Now the same health systems and strong immunization services can act as a platform to help fight poverty, too.But, with current estimates indicating that, by 2030, only half the world’s children will be fully immunized with the 11 vaccines recommended globally by the World Health Organization, we clearly still have some way to go. For our part, we are helping to change that.Since it was formed in 2000, GAVI has already helped to immunize more than 370 million children against a range of deadly diseases. As a result, we have prevented 5.5 million deaths, and we aim to immunize a further 245 million children and save five million more lives by 2015.At the same time, we now know that the value of vaccines extends far beyond the number of lives saved. Investment in vaccines is not about short-term savings, either in terms of lives or economic costs; it is about providing children with lifetime protection and the ability to realize their full potential. So, while reducing mortality is already reason enough to want to immunize every child on the planet, now we have the added motivation that we are not just saving lives, but also helping to improve many more lives in the process.Seth Berkley, M.D., is Chief Executive Officer of the GAVI Alliance, which works to immunize children in the developing world.www.project-syndicate.org