Via The Washington Post: Measles cases are spreading, despite high vaccination rates. What’s going on? Excerpt:
It’s now official: Measles cases in the United States are at their highest level since 2000, when the disease was declared eliminated — meaning that regular, year-round transmission had been interrupted. Five hundred fourteen cases have been reported this year — more than double the previous high, in 2011 — and the number is expected to continue to climb.
The measles vaccine is among the most effective, and the vast majority of Americans have either had the measles (and are therefore immune to a second case) or have been vaccinated against it. So why are so many people being infected?
One big reason is vaccine refusals: The overwhelming majority of current infections occur in unvaccinated people, most of whom declined the injections for religious, philosophical or personal reasons, according to the Centers for Disease Control and Prevention.
But 10 percent of the cases occurred in vaccinated individuals. Even worse, a case study published in February about a woman dubbed “Measles Mary” described a scenario that scientists had not known was possible: In 2011, the 22-year-old New York theater worker, who had been vaccinated, not only contracted the disease but also passed it along to four others, two of whom had also been vaccinated.
While this was very rare — it was the first documented case of a vaccinated person passing measles along to others — the case illustrates how the disease can pose a threat even to those who have had their measles vaccine.
Two ways to fail
What’s going on? Briefly, there are two ways vaccines can fail. To understand them, it helps first to understand how vaccines work.
Vaccines are made from a deactivated or weakened piece of a disease-causing pathogen — a virus or bacterium. When the vaccine is introduced into your body, it tricks your immune system into thinking it’s the real deal. The immune system ramps up and creates antibodies, which remain in your system until the day the real pathogen arrives . . . and then BAM! The disease is dead on arrival. That process — the body’s generating antibodies in response to a vaccine — is called seroconversion.
But sometimes the person getting the vaccine does not seroconvert: Antibodies are not created, and the person is not protected. This is the first way vaccines can fail, and it happens about 5 percent of the time with the MMR (measles, mumps and rubella) vaccine. That’s the reason for the second shot in the MMR series: After getting it, an additional 3 to 4 percent of people seroconvert, leaving 1 to 2 percent unprotected.
Parents who don’t want to vaccinate their kids may ask, “Why does it matter to you that my kids aren’t vaccinated if yours are?” The reason is that an unvaccinated child is more likely to catch a disease and then pass it on to others, including to someone who has been vaccinated but — because of failed seroconversion — is not fully protected.
So if vaccines can fail right off the bat, why bother with them?
Well, they fail in only a small percentage of the population. Seat belts don’t prevent death 100 percent of the time, and life jackets don’t prevent drowning 100 percent of the time, but they do reduce the risk of death; that’s why we use vaccines — for risk reduction, not risk elimination.