Vaccines, Herd Immunity, and Disease Re-Emergence – What’s the Deal?

By Michael Zingman

We hear about immunizations in the news. We are encouraged to get vaccinated. We hear friends and family talking about how they just “never got vaccinated” for something.

We then hear about outbreaks and re-emergence of vaccine-preventable diseases. So what is causing this re-emergence exactly?

Vaccines are one of the most crucial global health resources and are significant tools that can be utilized to protect large populations in both developed and developing nations from disease. Many diseases are vaccine-preventable, meaning if hypothetically everyone were to be vaccinated, the disease would become eradicated.

One of such eradicable diseases is measles. Measles was once “eliminated” from the United States; however, recently, there has been extensive media coverage over a measles outbreak within the country. Measles was eliminated but not eradicated because of a slight minority of people who went unvaccinated, and this number has increased and allowed the disease to return. These cases were found to be from parents who chose not to vaccinate their children, which ultimately harmed others.

Other parts of the world have also seen a re-emergence of vaccine-preventable diseases. One interesting case is that of Syria and the re-emergence of polio this past October. Polio had come extremely close to eradication in that area of the world; unfortunately, it has re-appeared. This was due to two key factors: 1) because of the ongoing civil war, the normal childhood vaccination routines have been altered or disrupted, and 2) polio has spread from Pakistan (which is one of the three remaining countries in which polio is still active), particularly through children, including those in refugee camps and those displaced in Syria. Polio has even spread to Iraq from Syria, and there is growing fear over proliferation of the crippling disease.

So why can just a handful of unvaccinated people lead to a wide-spread re-emergence of these preventable diseases? The key is herd immunity.

Herd immunity is defined by the Centers for Disease Control as when “a sufficient proportion of a population is immune to an infectious disease to make its spread from person to person unlikely; even individuals not vaccinated are offered some protection because the disease has little opportunity to spread within the community.” This concept of herd immunity is why widespread vaccination is necessary for prevention of these diseases. In an ideal world, everyone would be vaccinated for all of the vaccine-preventable diseases. However, that is not a practical situation (at least not at the current time). Herd immunity can be very effective in protecting large populations from these diseases, but often can be difficult to achieve as some diseases require greater than 90% of the population to be vaccinated. This threshold is frequently not met and populations are left vulnerable.

With a growth of anti-vaccination movements in the United States and around the world, some parents have stopped vaccinating their children. This has led to a decrease in herd immunity for these vaccine-preventable diseases, permitting their re-emergence. These movements have surfaced due to a growing fear that vaccines can have adverse effects on children. This fear has been augmented by conflicting information regarding vaccinations, as well as personal accounts of negative vaccine effects, including those by physicians. Misinformation has even led a significant portion of the U.S. population to believe that autism can be caused by vaccines. This belief became prominent in the 1990s and was one of the reasons cited for the growth of this anti-vaccination movement.

Two key aspects of the debate over vaccinations include a lack of information (or misinformation) and a mistrust of governments, health institutions and research agencies. These are major problems in the United States, but also in many countries throughout the developing world, including those countries in which GlobeMed partner organizations are located. A lack of research to disprove these supposed negative vaccine effects has made it hard for the public health community to convince people that no link exists. Furthermore, much of this research comes from pharmaceutical companies, leading to mistrust of this research due to potential biases. An overabundance of information also has prevented people from receiving direct information from health institutions regarding vaccine effectiveness and has caused them to educate themselves from other sources that are less reliable. On a similar note, there is a lack of public understanding about vaccinations that stems from a mistrust of health institutions. It can often be more difficult to vaccinate people in developing countries in which people view vaccinations as a corrupt government program. Some people even believe that required vaccinations for schools are done for the economic benefit of the government.

All of these issues discussed have increased fear of vaccines in many locations around the world, including in those places with GlobeMed partner organizations. Vaccine education needs to be expanded and effective national vaccination action plans need to be both developed and carried out to increase herd immunity. GlobeMed and its partner organizations, as well as similar global health organizations, need to empower communities around the world in order to enhance vaccination efforts. Education through vaccine information is necessary to present to the public why population immunization is essential and why a decrease in herd immunity can have tremendous negative effects.


World AIDS Day

To celebrate World AIDS Day, take a listen to the following inspirational StoryCorps presentation:

http://www.npr.org/2012/11/30/166162027/a-lifes-ministry-springs-from-a-dilemma-over-aids

For more coverage of the day’s events, news, stories, and to get involved, visit http://www.worldaidsday.org/

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