“These unvaccinated individuals are like the tinder that starts a roaring fire.”
A new NIH-funded study confirmed the association between vaccine refusals and recent U.S. outbreaks of measles and pertussis.
According to the study, « unvaccinated individuals comprised substantial proportions of cases in measles and some pertussis [whooping cough] outbreaks, and vaccine refusal — as measured by population-level vaccine exemption rates — was associated with an elevated risk for measles and pertussis, including among fully vaccinated individuals. »
The most common form of vaccine refusal is when parents claim non-medical exemption to a school's mandatory immunization requirements, says Saad Omer, Ph.D., M.P.H, professor of global health at Emory University and senior author of the study. Non-medical exemptions are given when parents claim the vaccines conflict with their religious beliefs or go against their personal or philosophical morals, and there has been a steady increase of them in the last 20 years.
« These non-medically exempt children make up 2/3 of those who are ineligible for vaccines, which includes people who can't get vaccinated for medical reasons, » Omer says.
Eric Risberg / AP / Via apimages.com
Measles was declared eliminated in the U.S. in 2000, but in 2014 there were a record 668 cases.
The study found that out of the 1,416 measles cases reported in the U.S. between 2000 and 2015, more than half (56.8%) were in unvaccinated individuals. And among those (for whom detailed medical records and the reasons for non-vaccination were available) 70% had a non-medical exemption from parents. More importantly, most of these unvaccinated cases make up the very dangerous « first wave » of the epidemic, Omer says, which is what triggers a mass spread.
Measles is a highly contagious disease spread through coughing and sneezing, which can cause a high fever, cough, red and watery eyes, mouth sores, and a rash. It usually goes away within three weeks, but in vulnerable patients it can cause pneumonia, brain swelling, and even death. The vaccine is 97% effective at preventing measles, so in rare cases vaccinated people can still be infected. « This is why vaccine refusal is so risky, because no vaccine is 100% effective even if everyone does the right thing and gets it, » Omer says.
Pertussis (whooping cough) hit a national low in 1977, but since 2005 there have been over 45,000 cases.
The study found that in eight nationwide pertussis outbreaks, between 59-93% of the cases were individuals who were intentionally unvaccinated or under-vaccinated (fewer than the recommended pertussis vaccine doses). Pertussis outbreaks have also happened among highly vaccinated populations, says Omer, which is evidence of a decreasing or « waning immunity » — and the only thing to combat that would be increased immunization rates.
Pertussis is a highly contagious respiratory tract infection that causes a severe, painful cough that can last for up to 10 weeks or longer. It affects all ages, but it can be especially serious and life-threatening in young children and babies. There is a multi-dose vaccine (Tdap) to prevent pertussis among unvaccinated and vaccinated individuals, who can still get a less severe form of the disease.
When too many people go unvaccinated, it can affect an entire population’s « herd immunity. »
Vaccination is intended to not only keep the individual safe and healthy, but the entire community population. When most of a community is immunized against an infectious disease, something called « herd immunity » happens, which means the chance of an outbreak is very low and it can be easily contained.
« Non-medically exempt unvaccinated people provide pockets of susceptibility which spread to everyone — they are the tinder that starts a fire, even among damp wood, » Omer says.
Alice Mongkongllite / Via buzzfeed.com