Some Latin American nations, as well as many African countries, have even lower immunization rates than the United States. Among the world's worst, for example, is the Central African Republic with only 25 percent, as well as South Sudan with 30 percent.
However, many countries have been more successful than the United States in vaccinating their 1-year-olds at least once. Among them are: Canada, Brazil, Bolivia, Uruguay, Paraguay, Cuba, Algeria, Morocco, Botswana, Zimbabwe, Tanzania, Egypt, Saudi Arabia, Iran, Kazachstan, China, Australia, Thailand, Russia, Kenya, New Zealand, nearly all European countries, Vietnam, Mongolia, Turkmenistan and Turkey.
That list is by far not exhaustive. It begs the question: Why do so many countries outperform the United States in immunizing 1-year-olds against measles? There are four key reasons.
- In many countries measles seemed to have been "eliminated." Hence, those countries (among them the U.S.) tend to "relax" about immunization. This, however, makes them vulnerable to renewed outbreaks, as the current cases show.
"Measles vaccination is sometimes the victim of its own success. When disease fades from memory and living standards rise, hesitancy to vaccinate children increases," Hayatee Hasan, a Technical Officer at the WHO, told The Washington Post.
- In developing countries the harm measles outbreaks can cause are still too visible to ignore. Parents and grandparents can see the change with widespread immunization — children are protected and no longer die from measles and complications associated with the disease such as blindness, or severe diarrhea.
Furthermore, many international organizations have devoted time and resources to vaccination programs, even in remote areas without health-care services. In countries hit by civil war, such as Syria, South Sudan or the Central African Republic, this has been much harder.
- Ongoing debates about the safety of vaccinations have prevented some parents in particular countries from becoming vaccinated. According to the WHO, this is a problem the United States shares with many other countries: Health-care workers sometimes encounter resistance among certain religious groups, typically those that prefer faith to modern medicine to cure or prevent illness.
- Some countries recommend doctors to give the first dose of measles vaccine at 9-months rather than at age 1 year, which increases the likelihood that those nations will have higher immunization rates for 1-year-olds. In fact, the U.S. Centers for Disease Control and Prevention recommends that the first dose of the vaccine not be administered to children less than 12-months old, but WHO recommends vaccination begin at 9-months.
However, higher immunization coverage does not necessarily mean that a country has higher levels of vaccine-derived immunity.
"Later vaccination is more effective. In the U.S., routine programs also give two doses, which increases the probability of successful vaccination, while many African countries rely on supplemental immunization campaigns to give children an opportunity for a second dose," explained Justin Lessler, an Assistant Epidemiology Professor at the Bloomberg School of Public Health.
It is not the United States that worries Lessler most. "The sub-Saharan African countries with low measles vaccine coverage are of the biggest concern," he said.
Graphics editor Lazaro Gamio contributed to this post.