We decided to visit a state beach and I had to the use the bathroom, which was (of course) something less than luxurious. There was a lot of graffiti on the door, but the most prominent was scrawled in permanent marker stating: “Hope you had your Hep C shot”. A more enlightened soul wrote beneath it “You can’t get Hep C from a toilet”. It’s a good thing I didn’t have a writing implement on me or I would have further defaced state property and written in large letters: “THERE IS CURRENTLY NO VACCINE FOR HEPATITIS C”.

I have heard a lot of very interesting stories lately about disease transmission and prevention. The vandalism in the bathroom was just the proverbial straw that broke the camel’s back. So to the set the record straight, here are a few facts:

Immunity- Immunity can be defined as “The condition of being immune, the protection against infectious disease conferred either by the immune response generated by immunisation or previous infection or by other nonimmunologic factors.” Since immunity is a condition of the body characterized by the immune system’s ability to recognize and mobilize a response to fight off an infection, it is based on an individual’s health and previous infection status.

For the most part, you can’t transfer your immunity to someone else because immunity depends on whether their immune system will recognize a particular antigen. One exception is breastfeeding because the antibodies from the mother’s bloodstream can transfer through her milk to her baby. But you can’t get a vaccine and pass the immunity it gives you to someone else- no matter what this column in Popular Science says about the oral polio vaccine in developing countries. (I’m still in awe that this sort of thing was published. You can’t pass your immunity to others and thereby strengthen the whole community. If that were the case there would be no need for high vaccination rates. Face+palm.) Other people would have to either acquire and recover from the infection or receive a vaccine to stimulate their immune systems to fight off an invading pathogen.

It also means that a vaccine is specific to a certain antigen. You can’t get a vaccine designed to create immunity for one disease and have it work against something completely different- which is where this news story gets off track when it claims that a flu vaccine would have saved this boy when he was infected with both flu and the deadly MRSA bacteria.

Herd immunity- Herd immunity is the idea that when a high level of vaccine coverage is reached (somewhere between 80-99%), that a particular illness will no longer strike a population and that this will protect those who can’t or won’t be vaccinated. Of course, levels need to be high- which is why the assertion that genital warts infections on the decline from the HPV vaccine is questionable. Low rates of coverage, by definition can’t confer herd immunity. However, other factors could have influenced the decline of genital warts infections like the advent of federal support for comprehensive sex education programs which occurred around the same time. Herd immunity also means that if the CDC is correct about the efficacy of flu vaccine (50-60% most of the time), even in a good year we won’t be able to achieve herd immunity, so please be careful with young babies and the immunocompromised.

Asympotmatic transmission/non-classical symptoms- You have to be very careful when you are around anyone immunocompromised or very young or old because vaccinated individuals who do contract an illness may not display classical symptoms (i.e. symptoms you would see in an individual who is not vaccinated who contracts the disease). Pertussis (commonly known as “whooping cough”) is one of these. Vaccinated individuals who develop pertussis often don’t display the “whooping” cough or may be completely asymptomatic. Measles is another. Vaccinated individuals who contract measles often don’t have a rash, but may have a stuffy nose and general malaise. (This called modified measles.) 

How often does this happen? Well, it’s hard to say. (After all, how often do you go into your doctor or pediatrician and say, “Even though nothing appears to be wrong, could you please run a complete set of tests to make sure that it’s not a case of non-classical pertussis or modified measles?”) A few years ago a survey taken during a pertussis outbreak in California showed that in 9 counties between 44 and 83 percent of the pertussis cases were in vaccinated individuals. The Journal of Emerging Infectious Diseases has study from Israel where a very young baby died of pertussis contracted at a daycare center where all the children and staff were fully vaccinated. Some of the children who tested positive for pertussis did not meet the WHO’s diagnostic criteria for the disease, yet still had it. The Journal of Infectious Diseases contains an article on two fully vaccinated doctors who had measles without the rash- the only reason that anyone considered testing them is because they had both been exposed to the disease. We do know that even individuals with non-classical presentation can pass the virus. It does happen, but on a wider scale it’s hard to quantify. So  the PSA is please exercise caution at all times.

Vaccine schedule- A vaccine schedule is what shots you get when. Here in America, I think we kind of assume that our vaccine schedule given by the American Academy of Pediatrics is the “gold standard”. There actually is no one vaccine schedule that has been agreed upon to be the “best”. The AAP’s schedule is pretty similar to Canada’s and Great Britain’s, though there are some notable differences. In Great Britain, they don’t routinely vaccinate for varicella (chicken pox) because when the varicella virus is not present, it increases the chance of older people developing shingles. If you take a look at the vaccine schedules throughout Europe, you’ll find that it’s a mixed bag. In some countries tetanus is recommended only for at risk populations. In several first world countries like France, Italy, Ireland, the Netherlands and Germany they don’t have rotavirus on their schedules (as of 2010). Varicella is absent from many countries vaccine schedule. Other countries add in diseases that are of special concern to them like Japanese encephalitis in many Asian countries. In the United States, there is kind of a philosophy that if there is even a relatively small risk for a disease, that we should err on the side of vaccinating for it. In other countries, a disease that has a relatively minimal risk may be viewed as having little upside for routine vaccination.

So why do we vaccinate for all these diseases, how do they spread and how do the vaccines impact transmission? Well, this isn’t an  exhaustive list, but here are a few. You may get a few surprises…

Tetanus- I’ve heard the wildest stories on when you need a tetanus shot. If you scrape your hand on a metal locker backstage in an auditorium, if you get a small cut from a nail holding down carpet inside a house, if you cut your hand on glass in your kitchen sink. One mom told me that after her child got a really bad scratch from a cat, she was told by a doctor at the ER that her kid needed a tetanus shot. All of the above scenarios are extremely unlikely to even impossible to lead to tetanus. Here’s why: Tetanus is caused by a bacteria called clostridium tetani. It lives in the feces of animals and flourishes in wet, warm and environments, especially like pastures. It causes infection when it enters the bloodstream through a deep wound. So rust and nails or other metal objects  actually have nothing to do with the infection itself. A rusty nail is a sign that the environment could be wet enough for the bacteria to flourish and stepping on one could cause a deep puncture wound that introduce the bacteria into the bloodstream. It’s not a communicable disease.

Polio- Quick: who invented the vaccine that is credited with eliminating polio? You said Jonas Salk didn’t you? Scientists and researchers now believe that it was a combination of Salk’s inactivated polio vaccine (IPV- the one you get through a shot) and Sabin’s oral polio vaccine (OPV- sugar cubes). (And depending on who you talk to, they might even give more credit to Sabin.) Salk had better backing because of his connection with Basil O’Connor, head of the National Foundation for Paralytic Polio (now the March of Dimes). Another reason the OPV has fallen off the radar in the US is that it was taken out of circulation in this country in 2000 because of vaccine acquired paralytic polio. In other countries, they still favor the OPV because the risk of provocative polio. (Provocative polio is when something like an injection or surgery during the high season for enteroviruses increases the chances of developing polio.)

Measles- Yes, this one can actually cause death, but who is most at risk may be a little surprising. According to the CDC, approximately 450 people used to die annually of measles in the pre-vaccine era. (Comparable to the number of people who die of salmonella poisoning annually.) Diagnoses of measles have been on the decline since the advent of the measles vaccine, but now those who do get it are more likely to die. The vaccine campaign has targeted young children, but adults (especially over age 30) are much more likely to develop complications or die. (The other group at greater risk are those with HIV/AIDS because they have compromised immune systems.) The other thing that may surprise you is the role of vitamin A in preventing complications with measles. The WHO recommends that all cases of measles be treated with vitamin A.

Mumps/Rubella/Varicella- Wow, wow, wow. I can not believe the number of times I have heard people say that massive numbers of children used to die from mumps and rubella. Mumps and rubella were actually not added to the vaccine schedule because of a high risk of death in children. In fact the WHO classifies, both mumps and rubella in as mild illnesses in children- it’s adults that tend to be the actual concern. They were actually added into the vaccine schedule because in teenagers and adults they can cause reproductive harm. In adolescent boys, mumps can sometimes infect the testicles causing impaired fertility. Deafness is another rare side effect of mumps, again more common in adults. Rubella itself isn’t the concern, it’s congenital rubella syndrome (CRS) that causes disability and sometimes even death. If a pregnant woman contracts rubella she can potentially pass the disease onto her unborn child and it can cause problems like blindness, deafness, developmental delays, and heart malformations. Varicella (chicken pox) is again a generally mild illness in children, but can be deadly especially for the immunocompromised. For women who do not have immunity, contracting varicella during the first 20 weeks of pregnancy carries a small risk of birth defects called congenital varicella syndrome.

Hepatitis B- I hear people say that you can be picking up trash along the side of the road, get stuck by a stray drug needle, develop hepatitis B and then DIE. This is not an accurate reflection of the transmission pattern of hepatitis B. Though there are a few very, very rare exceptions, hepatitis B is primarily transmitted in three ways: sharing needles during illicit drug use, high-risk sexual behaviors and maternal transmission either at birth or in the first few years of life. The good news is that in adults, 90% of hepatitis B infections will clear on their own without any complications. But for children it can lead to a chronic infection and possible further complications. Overall, there are relatively few children who have hepatitis B. Child-to-child transmission is well documented, in developing countries, but among developed nations child-to-child transmission of the infection is extremely rare. Because of the possibility that a mother could be carrying the disease and not aware of it, it has been added to many vaccine schedules.

Rotavirus-This story definitely paints a sensational picture of rotavirus, but it’s on the melodramatic side. In developing countries, diarrheal illnesses are a significant source of mortality because of malnutrition, dehydration, and lack of access to healthcare. However, in the US and other developed countries, the goal of rotavirus vaccination is actually to reduce hospitalizations due to severe rotavirus. However, there is a trade-off because some rotavirus vaccines like RotaTeq carry an increased of gastrointestinal illness over no rotavirus vaccine- though hospitalization is statistically less likely.

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