Why Vaccinate?

We live in a world fraught with dangers, but widespread death due to infectious diseases should not be one of them. These days we tend to worry about newly emerging infectious diseases like Ebola or Zika or whatever that disease is that turns people into zombies on the television show The Walking Dead.

While it is fine to show concern about serious emerging diseases like Zika, what about some old ones we thought we had gotten rid of like measles or mumps? What’s old is new again as we are seeing outbreaks of what used to be considered conquered childhood diseases. Diseases that had for years been very uncommon, are more recently appearing in alarming numbers.

Outbreaks of mumps have occurred in Hawaii  and Oklahoma  while measles has become a problem in Minnesota. Colleges are sounding the alarm and requiring students to be vaccinated for a variety of infectious diseases once thought to be largely eliminated from the US population due to many decades of aggressive vaccination programs. While the occasional case is to be expected, these large outbreaks signal something new that health officials are scrambling to contain. These diseases, nearly unheard of for decades, are now making a comeback. This is quite unfortunate as these diseases are almost entirely preventable.

Decades of misconceptions about the dangers of vaccination have led a generation of parents to opt out of childhood vaccinations. Fear of vaccination has been around since the advent of widespread use of vaccines. Even with decades of evidence showing the effectiveness of such programs, the fear of vaccination persists to this day.

Every year people immigrate, or come as part of refugee resettlement, from parts of the world where vaccination programs are not as effective. Through all of these ways the number of unvaccinated people can increase which allow pockets of susceptible children and adults to form in cities and neighborhoods. When a case appears of a particular disease it quickly spreads to others in that location who are susceptible. Given the medical tools at our disposal we should be able to control the spread of infection among large numbers of people.

What can be done?

The main goal then centers on the prevention of epidemics, a term used to describe an infection that occurs more frequently than one would expect it to. Influenza cases typically increase dramatically in the winter months but are far less common in the summer. A large change in the expected number of cases in the winter or summer would signal an epidemic outbreak.

The question then becomes: How to control epidemics? After all, some infectious agents will do more than make you sick for a few days, some you will not survive. Even influenza is lethal to tens of thousands every year, typically among the very old or very young. But other infectious agents are lethal to all age groups so preventing epidemics literally becomes a matter of life or death.

When it comes to dealing with infectious agents there are a couple ways to approach the problem. One can wait till a person is sick and then treat them with drugs. Or, one can take steps to ensure the person never gets sick in the first place. The advent of antibiotics revolutionized the medical treatment of infectious disease. If someone today gets an infection, the use of antibiotics can kill the organism (provided it is not a virus) and the patient won’t die. However, there is another mechanism for dealing with infectious disease, the human immune system.

Prior to the advent of antibacterial and antiviral drugs there was only one method for dealing with disease, the innate immunity of the individual. Those infected were quarantined and doctors hoped the patient would survive by treating the symptoms as well as they could. Unfortunately, many times an infected person would die, so the method was hardly foolproof.

However, as doctors and scientists noted at the time, those who did survive tended to never again become ill. A survivor could become immune to certain diseases. Modern day vaccination takes advantage of this phenomenon. The idea is to expose a person to an infectious agent, in a way that won’t kill them, but will merely let their immune system work its magic and cause the person to become immune. Prior to the introduction of antibiotics, vaccination programs were the only option for public health organizations. Even today, this is the preferred method when dealing with viral diseases.

The Importance of Herd Immunity

Immunity works at the level of an individual. If everyone were immune to a specific infectious agent, then an epidemic would be prevented. However, in any human population, it’s impossible for everyone to become immune. Just like ancient doctors noted how some people survived a plague and others did not, variation exists and some people are more susceptible to infectious diseases than others. Aside from simple genetic variation, some people in a population are more susceptible to infections due to age or other health conditions. Very young children have underdeveloped immune systems. As one ages, the immune system slowly becomes less effective. Still others have complicating factors like cancer or diabetes or other physiological diseases that weaken their immune system. In other cases a person could be allergic to a specific vaccination, so they can’t get it, or the vaccine simply may not work. While rare, these cases do exist so some people cannot be immunized even though they would prefer to be.

It is not possible to have everyone in a population immune to a given infectious agent. To stop an epidemic however, it’s only necessary to have most people immune. This concept is called Herd Immunity. If enough of a population is immune to an infectious agent then epidemics can be prevented. Some will still get sick but the disease will not spread wildly through the population. In order for an infectious disease to spread it has to travel from one susceptible person to another. If a sick person only comes into contact with others who are immune, they will not ‘catch’ the disease and they won’t spread it to others who are susceptible. The only way epidemics happen is when too many people are not immune and it spreads from one person to another to another and so on. If enough people are immune, then it becomes unlikely than an infected person will randomly encounter another person who is not immune and pass it on to them.

Problems arise when some people voluntarily choose not to become immune. After all, if the infection is not common what is there to worry about? Even if that person becomes infected, it’s their personal choice and they’ll deal with the consequences. Unfortunately this ignores the underlying principle of herd immunity. Not only does an unvaccinated person run the risk of getting an infectious disease, they can also spread it to a person who, for whatever reason, cannot become immune through no fault of their own. So a person who willingly refuses to become immune is not merely a threat to themselves, they reduce the herd immunity of the group to the point where epidemics can happen.  This exposes anyone who cannot develop immunity for whatever reason. That “personal choice” now becomes a potentially fatal threat to others.

So, are Vaccines Safe?

Frankly it depends on what the definition of safe is, and that’s a difficult discussion. ANY medication comes with the risk of potential side effects. A person can have an unusual allergic reaction to any medication even if millions of others will not. This potential consequence has to be weighed against the possibility of complications due to infection. Some diseases like chickenpox have pretty mild effects though a child can die of complications. Other diseases have a much higher mortality rate.

Measles vaccinations have significantly reduced deaths worldwide from 2.6 million deaths in 1980 to half a million by 1990, down to 73,000 in 2014.  One has to weigh the rare but possible side effect of the vaccine against the more likely event of becoming infected with an organism that could very possibly cause death. It’s all a matter of weighing one risk against the other keeping in mind that failure to vaccinate not only threatens the person at hand but also all the other people who could be exposed if that person does in fact become sick and contagious. Without good herd immunity the entire community is at risk, not just a few individuals.

Unfortunately, there are those who strongly advocate against vaccination. Ironically, the very success of decades of vaccination has led to the conclusion by some that these diseases are so rare they are no longer a threat. Most people today have no recollection of the horrors of polio that affected our grandparents or great-grandparents just a couple of generations before us. That makes it easier to believe studies that have come out in recent decades showing a link between vaccines and autism.

The original study that proposed such a link was studied and referred to by many subsequent studies. Some showed a link between autism and vaccinations, others did not. Eventually the debate became so intense that researchers had another look at the original study, the one so many others based their conclusions on and found it to be deeply flawed. In an unusual move the original journal that published the research retracted the study as poorly done and statistically fraudulent. Still, by then the meme had taken on a life of its own due to social media and others in positions of authority pursuing their own interests in promoting this false idea. Even worse, celebrities  became involved in the anti-vaccine cause. This notion of  vaccines causing autism has become so ingrained that some people won’t vaccinate their pets for fear of fluffy becoming autistic. Of course animals cannot be diagnosed as autistic so it’s rather a moot point.

What Does All of This Mean? To Vaccinate or Not to Vaccinate?

Vaccination programs are undeniably effective. It is true that while some individuals experience side effects that can be very significant, there is no evidence that serious side effects are widespread. Even so, this has to be balanced against the possibility of a person contracting an infectious disease that will also have very serious side effects up to and including death. In addition, infected individuals will also pose a threat to anyone around them who is also susceptible to the disease. One has to weigh the risks to a small number of individuals to the risk of an epidemic that may kill hundreds or thousands. Looking back into history we can see the death toll these infectious diseases used to routinely wreak on population centers all around the world. Life expectancy has risen dramatically worldwide in the last hundred years largely due to the control of killer infectious diseases. Antibiotics have surely played a large role in that but so have vaccination programs.  In a recent report the World Health Organization  indicated that we are not making enough new antibiotics in an era where antimicrobial resistant organisms are becoming more common. And for viral diseases, for which antibiotics have no effect, vaccinations are the only defense against epidemics. Vaccination will be a key component of our ability to control infectious disease outbreaks for the foreseeable future. While managing potential side effects to vaccines continues to be an issue for consideration, the preponderance of evidence suggests that the benefits of vaccination outweigh the risks.

Additional Information


  • Zombies – By Eddy BERTHIER from Brussels, Belgium (Zombie Day 6 – Bifff 2012) [CC0], via Wikimedia Commons
  • Do Not Vaccinate! – The College of Physicians of Philadelphia’s Historical Medical Library (public domain)
  • Quarantine and Vaccination posters – CDC

Article by Michael Troyan. Michael has spent 20 years teaching non-majors biology and microbiology and currently works as an online instructor at Penn State University. He can be reached at [email protected]. For more articles by Michael, see our contributors page.

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