— -- This week, the World Health Organization kicks off World Immunization Week "to promote the use of vaccines to protect people of all ages against disease."
In the U.S., overall vaccination compliance remains high for many childhood immunizations, with at least 90 percent of children getting the recommended vaccinations on time for measles/mumps/rubella, polio and chickenpox, according to a 2015 report from the U.S. Centers for Disease Control and Prevention.
However, the CDC found other vaccination rates fell below its target for what's known as herd immunity, or a population's resistance to the spread of a disease that results when a high percentage of individuals are immune. This included below than ideal vaccination rates for diphtheria, pertussis, and tetanus (80 percent), hepatitis B (89 percent), and the gastrointestinal disease rotavirus (68 percent).
In recent years, outbreaks of vaccine-preventable diseases like measles or pertussis have made headlines, revealing how pockets of unvaccinated or undervaccinated people may still present a problem.
In the last year, there has been a huge upswing in the number of mumps cases in the U.S. In 2016, there were multiple outbreaks of the mumps resulting in 5,748 total reported cases in the U.S. Comparatively, there were just 229 cases in 2015. Washington state has had 771 mumps cases since the start of an outbreak last October.
Earlier this month, Texas reported an outbreak of mumps that infected 221, the highest number since 1994, when 234 cases were reported, according to the Texas Department of State Health Services.
Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, said in an earlier interview that the recent mumps outbreaks appear to be occurring in populations with high vaccination rates.
"Although people are vaccinated, after about 15 years, there is some waning of immunity and if you get a strong exposure that exposure can overcome that diminished protection and you'll get a case of mumps," said Schaffner.
The CDC has confirmed that its Advisory Committee on Immunization Practices (ACIP) is reviewing vaccinations for mumps and considering recommending a booster shot during an outbreak.
There have been multiple measles outbreaks in recent years that have infected hundreds in Ohio, California and Minnesota, according to the AAP. On Monday, the Minnesota Department of Health reported at least 20 children under the age of 5 have been infected with the virus. Currently, 16 of these children have been confirmed to be unvaccinated against the virus.
Once a measles outbreak starts in an area with low vaccinations, it can be difficult to control, according to the CDC. Measles is one of the most infectious viruses in existence. It will infect 90 percent of susceptible people if they are exposed. The airborne virus can also remain in the air for hours, infecting people if they are in the same vicinity as someone who is ill, according to the CDC.
The measles virus was declared eradicated from the U.S. in 2000 and reached an all-time low with just 37 cases in 2004.
Whooping cough or pertussis has been significantly reduced by vaccines but continues to occur, since the vaccine's effectiveness decreases over time. Approximately four years after getting a vaccine for whooping cough, just three or four out of 10 people are protected against the virus, according to the CDC.
The CDC reports that there are between 10,000 to 40,000 cases of pertussis every year and up to 20 deaths.
In California, a massive outbreak of pertussis infected 9,934 in 2014. Just two years earlier, Washington state reported 2,530 cases, according to the AAP.
California gets tough about vaccinations
There has been some good news on the vaccination front. This month, California reported that the vaccination rate for kindergarteners had hit "a new high," rising from 93 to 96 percent after the state government made it tougher for parents to opt out of vaccination compliance.
Art Caplan, head of the Division of Medical Ethics at NYU School of Medicine at the Langone Medical Center, said the state of vaccination success in the U.S. is "mixed" but that California has been a bright spot.
"They've done an amazing job and one that might inspire other states in getting better reduction in the measles," Caplan said, who co-authored the book "Vaccination Ethics and Policy."
In Marin County, where much of the pertussis outbreak had spread in 2014, the vaccination rate has climbed dramatically from 77.9 percent of kindergarteners being in compliance to 93.2 percent today.