(Photo courtesy of ThinkStock)
Sometimes it’s good to be part of the herd.
That’s especially true when it comes to immunizations, and it’s a good thought to keep in mind as schools (aka germ factories) reopen across the area on Tuesday.
In general, the greater the number of people who are vaccinated, the higher the rate of herd immunity. The colorful (if less-than-flattering) term describes how a whole group becomes less susceptible to a particular illness if enough of its members are immunized. That’s true whether you’re talking about a herd of cattle or a nation of people.
If, for instance, someone within a group contracts whooping cough and a certain threshold percentage of that group has been immunized, that sick person is easier to isolate and the illness less likely to spread. For that reason, herd immunity helps keep healthy a population’s most vulnerable members – the elderly, newborns, and people with compromised immune systems.
Herd immunity generally applies to diseases spread through people-to-people contact.
You're never going to get 100 percent herd immunity, though. Some people, for a variety of medical reasons, can’t receive a vaccine. Some people simply don’t bother, and others (wrongly) object to vaccines as health hazards. Compounding the problem is that no vaccine is 100 percent effective.
Measles are a case in point. A highly infectious, airborne disease, measles can be spread through a cough or sneeze or by touching an infected surface. The CDC says that there’s a 90 percent chance of infection if a non-immunized person is in close contact with someone with measles.
In April, the Centers for Disease Control [CDC] reported that there were 159 measles cases associated with an outbreak tied to exposure at Disneyland in California. Twenty-two hospitalizations resulted.
According to the CDC and its Morbidity and Mortality Weekly report, 131 of the patients “were either unvaccinated or didn't know their vaccination status.”
“Of the 68 Americans in the unvaccinated group, 29 cited philosophical or religious objections, 27 couldn't be vaccinated because they were too young or had a medical contraindication and 12 weren't vaccinated for other reasons.”
That’s a lot of cases, but they were isolated, because the vast majority of the population has gotten its shots.
The overall number of measles cases so far this year in the United States is actually shaping up to be well below the number reported in 2014, according to the CDC. As of Aug. 20, there had been 188 reported cases of measles. In all of 2014, there were 667. Here’s a map of the states showing incidents of the disease:
So, how well protected are your kids?
The CDC reported in August that the national vaccination rate in the past school year was high, with a median of 94 percent in kindergarteners. The rate in Virginia (93.4) was just a bit below the national median.
That’s adequate, according to James Farrell, director of the Virginia Department of Health Division of Immunizations. Herd immunity is usually conveyed at 65 to 96 percent immunization, with a rate at the higher end needed in regards to measles, Farrell said in a phone interview on Monday.
One concern is the increase in the number of Americans opting out of vaccinations over health concerns. Requirements vary by state, but immunizations are mandatory for school attendance. Exemptions are allowed, and they vary by state.
Nationally, about 1.7 percent of the population has exemptions from required immunizations, according to the CDC. That’s low, but, as the CDC notes: “geographic pockets of low vaccination coverage and high exemption levels can place children at risk for vaccine-preventable disease ...”
Virginia has one of the lowest exemption rates in the nation, Farrell notes. But the number is on the rise. According to a CDC report, .6 percent of Virginia’s school-age population was granted an exemption to immunization requirements in the 2013-2014 school year in Virginia. In the last school year, that percentage nearly doubled, to 1.1 percent. Most of the exemptions in Virginia are categorized as religious (891) versus medical (395).
Schoolchildren can be exempted in Virginia if parents sign a notarized waiver asserting vaccinations are against their religious beliefs. It’s relatively easy to get, and in some situations, it’s more of a philosophical stand than a religious tenet, but as Farrell notes, it hasn’t created a problem.
He’s more concerned about our immunization rates against pertussis, better known as whooping cough. It’s also a highly contagious bacterial infection. Adults who contract whooping cough generally display symptoms akin to a bad cold, Farrell says, but it can be deadly for infants.
Farrell stresses the importance of making sure children receive the five mandatory doses of vaccine before they attend school, and notes that the adults in a newborn’s life, including grandparents, need to be up-to-date in their booster shots.
For adults, that immunization is known as the Tdap (a booster against tetanus, diphtheria and pertussis). The combination has only been around since 2005, so if you think you had a tetanus booster before then, you and your child or grandchild are not protected against whooping cough.
Older children also need to be current in their vaccinations. Immunization is lagging in vaccinating adolescents against HPV, the human papillomavirus, the most common sexually transmitted infection. It can cause genital warts and cancer.
Some parents fear the vaccine sends a wrong message and encourages sex before marriage. Many are concerned over safety of the vaccine itself – an unfounded fear, Farrell says.
It’s the first cancer prevention vaccine available, but it’s not catching on, he noted, here or across the nation.
An array of websites provide information regarding health risks of vaccines; so many, in fact, that Farrell calls the Internet “our enemy.”
He notes that there are years of rigorous screenings of any vaccine before it’s approved, and that there are ongoing safeguards and follow-ups to ensure safety. You can see CDC’s list of common questions regarding the HPV vaccine safety here.
“The whole intent of giving (the vaccine) at that age is to get them (immunized) before they are exposed to the virus,” he said. “By not vaccinating our kids with the HPV vaccine, it’s a tragedy.”