More than 300 million individuals worldwide suffer from major depression. About 16 million of them are in the U.S., where 90 percent report difficulties with work, home or social activities related to their symptoms. While there are many effective treatments for depression, including medications and psychological therapies, the rate of depression is not going down, and treatment is not enough to reduce the burden. Recently, research has emerged indicating that about half of all cases of depression are preventable.

Yet we’re not doing much to prevent it. In much the same way we vaccinate against other debilitating diseases, it is our moral obligation to begin concerted prevention efforts to reduce the number of new cases of depression in our communities.

Depression is the number one cause of disability worldwide. It produces substantial suffering not only for the depressed individual, but also for those around them—when it leads to suicide, the impact on surviving loved ones is devastating. Depression is also related to a number of other health problems. Take smoking, for example, which is the leading cause of preventable death in the world, and how it is affected by depression. People who suffer from depression are more likely to start smoking, less likely to quit, and, if they quit, more likely to start again. This is the case with the use of alcohol and other drugs as well. Adolescent girls who have suffered at least one episode of major depression have a greater probability of having sexual relations as teenagers, having more than one sexual partner and having unintended pregnancies.

The benefits of preventing depression would go far beyond mental health. The good news: there is a way to prevent it.

Effective psychological interventions such as cognitive behavioral therapy, which teaches patients skills that give them greater control over their mood, have been found to reduce the likelihood of having another depressive episode in the future compared to antidepressant medications, once treatment stops. This preventive effect led researchers to ask, “Why wait until people are clinically depressed to teach them these skills?” In over 40 randomized controlled prevention trials to test this question, the evidence has been mounting that we can prevent about 50 percent of new episodes of major depression in people at high risk of becoming depressed in the near future. If we did this at the community level, the impact on our nation’s health would be massive.

Some critics say that we cannot prevent depression until we understand its causes, and that we are still far from doing so. But we have already found effective treatments without a complete understanding of how depression works. There is a famous public health story that describes how John Snow stopped a cholera epidemic in a neighborhood in London by figuring out that the people getting sick lived near a water pump. He removed the pump handle and the epidemic in that neighborhood stopped. The cause of cholera was not known then. Similarly, intervening with methods that have been shown scientifically to treat and prevent depression makes sense.

Others argue that we should wait until we have methods that are more effective than reductions of 50 percent. But we spend many resources on flu vaccinations, even though they are only effective in preventing 30 percent to 60 percent of cases, depending on the strains that are active each year. Given the burden of these diseases, even preventing a substantial portion of new cases makes both economic and humanitarian sense.

Beginning a concerted national effort to prevent depression will require using strategies that can scale up and are inexpensive, in addition to in-person forms of preventive interventions based on traditional psychotherapies. Internet interventions have been shown to work in the treatment of depression, and some early studies indicate that they can also be effective in stopping new cases, including one randomized controlled study from Germany that shows that new major depressive episodes can be prevented using online interventions.

With this knowledge, our research group has argued for the creation of digital apothecaries; that is, online portals that would provide access to massive open online interventions (MOOIs), similar to MOOCs, or massive open online courses. These MOOIs would provide evidence-based health interventions to anyone wishing to use them at low or no cost, including interventions that teach users mood management interventions to prevent or manage depressive episodes.  These digital interventions would adapt the work already done in face-to-face preventive studies that have shown that new episodes can be prevented in people at risk for depression.

By developing, evaluating and disseminating in-person interventions as well as websites and mobile apps designed to prevent depression, we will take an important set of steps in the long road toward a world without depression.