It is sometimes challenging for some of us that have been raised during the years of enormous vaccination efforts to understand the widespread incidence/prevalence of infectious diseases such as measels, diptheria, pertussis, polio, etc., to name just a few. In fact, during the 1900’s cases of each of these numbered in the hundred of thousands in their peak, claiming thousands of lives each year. Thankfully, due to the advent of vaccines, there has been remarkable progress in the attempt to eradicate these deadly diseases. However, in order for vaccinations to have there fullest potential parents need to abide by the vaccination recommendations to assure herd immunity and optimize the prevention of disease, transmission and deaths. Surprisingly, even with this biomedical achievement, there are parents that are hesitant to follow the vaccination schedule. I think one obstacle is that some parents may lack understanding of what vaccines are and how they can be useful to protect their precious children.
Gratefully, our bodies have a natural way to protect us and acquire immunity when exposed to infectious agents. The principle behind immunization is to mimic the events that are normal to the adoptive immune response. The protection provided by immunization are artificial but it can either be passive or active. According to our text Nester’s Microbiology, artificially acquired passive immunity can prevent disease or limit the duration of disease by injecting a person with antibodies produced by other people or by animals. However, artificially acquired active immunity results from exposure to antigen/vaccine that amounts an immune response, including memory B cells for lasting protection.
Vaccines not only protect an individual against disease but they can also prevent diseases from spreading in a population. This is because of a phenomenon known as herd immunity, where the vaccination of sufficiently high enough members of a population prevents the spread of a contagious disease within a population. Furthermore, herd immunity is credited for the dramatic declines in a lot of the childhood diseases, both in the United States and in developing countries. We can credit herd immunity because we can see the unfortunate instances where diseases reappear and spread as a direct consequence of parents’ failure to have their children vaccinated. For example, in 2019 there was a surge of measles cases in the US and the world, the greatest numbers reported since 1992. The report supports that the majority of cases were unvaccinated people. Polio, is another example of still having some cases in Endemic countries often due to lack of access to vaccine. The question then remains, why wouldn’t all parents take advantage of immunization programs so we can get rid of these preventable diseases? Both clinical trials and national agencies have provided data that support the safety and efficacy of vaccines so parents have resources available to aid in their decision making. Also, adverse events are routinely reported to help monitor safety control. Therefore, I think parents can benefit from understanding what makes up a vaccine and the characteristics that make them so valuable.
One feature of vaccines can be categories into two types, whether they are attenuated or inactivated. An attenuated vaccination agent can replicate within its host, promoting the production of memory B cells and affording longer lasting immunity; whereas an inactivated vaccination agents cannot. For example, the polio vaccine has two variations that include both of the aforementioned types. Historically, there are three known serotypes of poliovirus that have developed vaccines, any of which can cause the disease. One type is originally called the Salk vaccine and it was developed in the mid-1950s, consists of inactivated virus particles of all three serotypes. The newer more common name for this vaccine, is the inactivated polio vaccine (IPV). IPV has been shown to successfully lower the rate of the disease dramatically but had the disadvantage of requiring a series of injections for maximum protection. This is especially difficult and less appealing in developing lands where access to vaccines are not so readily available. The solution, in 1961, the Sabin vaccine became available. The more common name today for this vaccine is the oral polio vaccine (OPV), which consists of attenuated strains that replicate in cells that line the throat and intestinal tract. This vaccine has the advantage of cheaper oral administration, often requiring only a couple doses and offers longer lasting immunity. However, there are some disadvantages of attenuated agents that need to be considered, especially for immunocompromised individuals. There are times when the agent can mutate to become pathogenic again and can even cross the placenta to damage an unborn child. Also, since the agent is active they require refrigeration, a luxury not always attainable in developing countries.
So what has been the results of vaccinations such as the polio vaccine? Well, polio has been eliminated from the United States due to the miraculous recommendations to use the OPV for over 40 years, from 1963 until 2000. Because of this, today, there isn’t wide-spread vaccination needed, however, since 2000, only IPV is recommended to prevent polio in the United States. In most other countries utilizing vaccines, the results have been similar. Sadly, some countries are having to deal with the impact of polio. So far in 2020 there are 20 reported cases of polio globally, apparently all in Pakistan. There has been a resurgence of polio with wild poliovirus cases increasing from 12 in 2018 to 144 by the end of 2019. Therefore, to affirm a sense of urgency, just last week, “the current Secretary-General of the United Nations (UNSG) António Guterres visited a kindergarten school in Lahore, Pakistan during the first nationwide polio campaign of the year and vaccinated students with the polio vaccine. More than 39 million children across the country are set to be vaccinated during the February campaign.” There are extensive campaign efforts to eradicate polio in as little as within the next 3 years. I think his visit is timely and the implementation of the Pakistan Polio Eradication Programme is bound to lead to re-evaulations in the way we think about the disease and make us all world-wide better able to respond to way that we can prevent increased virus transmission.
Microbiology and You 