There are a several reasons for the lack of progress in immunizations, including the cost of vaccines, weak health systems and lack of access in poorer countries.

Jean-Marie Okwo-Bele, head of WHO's vaccine unit, said, "This is of grave concern. There are still 1.5 million premature deaths due to vaccine preventable diseases each year. Today WHO is calling for the global community to close the immunization gap and the unnecessary disability and deaths caused by the failure to vaccinate. The world has made great strides in recent decades in raising immunization rates, from as low as 5% in some countries in the mid-1970s to a global average of 84% in 2013. And 129 countries boast immunization levels above 90%, with vaccines estimated to save as many as three million lives each year. But the progress had been plateauing in recent years, despite a commitment in 2012 by all WHO members to a plan to ensure all children are immunized. There are a number of reasons for the lack of progress, including the cost of vaccines, weak health systems and lack of access in poorer countries. Armed conflicts and insecurity also limit access, as do emergencies like the west African Ebola outbreak, with recent, unverified numbers indicating that immunization levels in Guinea, Liberia and Sierra Leone dropped as much as 30 percent at the height of that crisis."
Also, the researchers pointed out that in developed nations, where coverage is generally high, there are pockets where rates are low, as recently emphasized by measles outbreaks in the United States and other western countries. They said last month that immunization rates as low as 50-86% had made the US outbreak possible. In wealthier countries the low rates of vaccination can be due to the fact that many of the deadly diseases being vaccinated against rarely appear, and are no longer feared, allowing complacency to set in.
Philippe Duclos, WHO senior health advisor, "A number of parents also refuse to vaccinate their children against measles, mumps and rubella, claiming it is responsible for increasing cases of autism, a theory repeatedly disproven by a range of studies."
Source-Medindia