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Guest Post: Specific vaccines and their effectiveness

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(This is is the fifth in a series of guest posts by Dr. Mark McColl answering reader questions about vaccinations.  Please read my vaccine history and introduction of Dr. McColl before reading this post.  You might also like to read his earlier posts on his vaccination choices for his kidsethics and parental rightsdelaying vaccinations, and kids that need special consideration.)

Why are there so many more vaccinations today than 30 years ago?

The number of vaccines has increased over the years as the science and technology has advanced to allow for further and better protection.  Just car and airplane safety has increased with emerging technology, the science of building a vaccine against a deadly organism has advanced.  When certain specific markers on these organisms are identified the process of replicating those markers in such a way that our immune system can and will recognize them begins.  Many of the tried and true methods that are already in place are used but each vaccine is unique in what protection it provides.

It is very clear from the domestic and international data that as the number of organisms against which we are able to vaccinate increases the childhood morbidity and mortality rates decrease.

Why do our kids need to be vaccinated against chicken pox when we weren’t?

Childhood occurance of chicken pox (varicella zoster) infection used to be common place.  Many of us remember the “chicken pox parties” our parents organized to allow for the spread of the virus.  As a disease spread by respiratory particles merely being in the same room with an infected child is sufficient to cause infection.

Childhood infection itself is fairly miserable.  Common complications of primary varicella infection are things such as skin infection from invasive group A streptococcus bacteria (the same bug that causes strep throat can infect the skin), scarring of the pox marks, encephalitis (infection and inflammation of the brain), Reye syndrome (a form of liver failure often associated with aspirin use while infected), and pneumonia.

All of these complications become more common when the person has a weak immune system.  Ironically, all of these complications also become more common as we age.  In my career, the last patient who had his initial chicken pox infection as an adult had the classic pox marks on the lining of his intestines and the surfaces of his lungs.  He was hospitalized for this for about three weeks.

Primary chicken pox in a pregnant woman also has serious implications for the child.  Scarring of the skin can occur while the child is in the womb as even there the pox marks occur.  Brain damage and mental retardation occur as well as eye damage and low birth weight.  Mortality rates for this infection are around 30% and about 15% of children will develop herpes zoster (shingles) by their fourth birthday.

The last, but not the least significant, reason for vaccination is to try and prevent our children from suffering herpes zoster (shingles) as an adult.  As a member of the herpes family of viruses like the virus that causes fever blisters and the virus that causes mono, varicella virus lives within us forever.  Under times of stress or weakened immune systems (read: old age) this virus can reactivate and cause painful nerve damage and the characteristic blistered rash along a particular nerve path.  If the person is fortunate the body responds and resolves the flare up over several weeks.  If not, then the nerve is permanently injured and the burning, searing pain of an angry nerve never goes away.

Why do people who are vaccinated still contract the diseases?

Vaccine effectiveness can be measured in several ways.  It is often contended that vaccines are only effective if they prevent someone from acquiring the infection against which they were created.  In general, vaccines are pretty good at doing that.  I often quote the ad hoc statistic that on average a fully vaccinated individual who is otherwise healthy won’t get the disease we are trying to protect against about 85% of the time they are exposed.  That’s not a scientific number but rather my professional experience when considering all vaccines a typical child receives.

Some vaccines have a really high protection rate approaching 100% and some vaccines are much lower. For instance inactivated polio virus vaccine provides something like 50-60% protection.  This doesn’t sound like much but has been sufficient to allow most industrialized countries to virtually eradicate polio.  If you were going to travel to Africa or India where it is still endemic you might consider getting the oral polio vaccine.  It has a much higher protection rate.  So is inactivated polio effective (because there hasn’t been a case of wild polio in the United States since the 1990’s) or is it ineffective (because the protection rate is only 50-60%)?

Of course many factors go into whether or not a person is well protected.  Sometimes the immune system doesn’t develop an appropriate response to the vaccine just like the immune system doesn’t always protect us against invasive infections.  Poor nutrition and other metabolic stressors like concurrent infection or systemic steroids will alter our response.

The key aspect of vaccine effectiveness in my view is not necessarily how often I’m protected from acquiring the disease for which I was vaccinated but rather how often I don’t die or become disabled from the disease.  Generally speaking the rate of death from a disease for which we are vaccinated is less than 1%.  That’s a dramatic drop from the rate of death and disability from the disease itself.

Which vaccines are the least effective?

For the otherwise healthy individual, probably the least effective vaccine on its on is inactivated polio virus vaccine for the reasons already mentioned.  If you consider that the majority of people in their 70s and 80s have a very poor immune system and do not respond to vaccines then we might say that the standard dose influenza vaccine is the least effective for them.  For the 2012-2013 influenza season we only documented about a 9% protection rate in this age group.  Now if these people had received the recommended higher dose influenza vaccine who knows.  We also don’t know what the number would have been if all of those vaccinated had been exposed to only the strains in the seasonal vaccine.  Some of them contracted strains not in this season’s vaccine so there was no added protection.  In an average year in the United States, over 45,000 people will die from influenza infections and their complications.  In that same average year, only 35,000 will die in car accidents.

I’ve made the analogy before but vaccines and car safety are similar in many ways.  Most times you’ll go for a trip and never ‘need’ your seltbelt.  Then every now and then you’ll have a car accident where the seatbelt will save your life.  Once in a great while, you’ll wear your seatbelt and still die in a car accident.  Even rarer still the seltbelt will cause you to be trapped in your car and you’ll die.  If you hadn’t worn it you would have escaped.  How do you predict which one will happen to you?  You can’t.  You can look at the odds though and realize that on most days for most trips you’ll either not need your seatbelt or it will save your life.  The least likely outcome is that your seatbelt will hurt you.

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