There is considerable concern about the potential risks associated with vaccines.  Vaccines have a very good safety profile and mild side effects, if any. Yet all drugs, including vaccines, pose a risk and can be lethal to a susceptible person. (See “It’s the Pink One,” 24 January 2020.)


Infectious diseases have ravaged populations since time immemorial. Before the advent of vaccines, epidemics and pandemics wiped out large segments of the population. (See “Black Swan Events”, 4 September 2020.)  The current coronavirus pandemic is a replay of pandemics of the past. As of 19 September 2020, in the United States alone there were over 6,700,000 cases of Covid-19 and 198,000 deaths from Covid-19 ( Once upon a time, measles, mumps, rubella, and chickenpox were also rampant, if less deadly.

Prior to the development of a measles vaccine in 1963, every year in the United States measles infected about three to four million people – including about 90% of all children.  It caused viral encephalitis (infection of the brain) in about 1000 cases, and led to about 400-500 deaths every year (CDC, 2018; Leung, et al., 2018).  In the year 2000, measles was declared eradicated in the United States as a result of immunizations.  Unfortunately, fear of vaccines has led some parents to refuse vaccination for their children.  This fueled the resurgence of imported measles seen in 2018.

Chickenpox (varicella zoster) is endemic world-wide. This virus is extremely contagious.  Prior to the development of a vaccine, approximately four million of the U. S. population became infected with it, leading to about 10,000 hospitalizations and 100-150 deaths every year (CDC, 2019a; Spencer, 2017). Unlike measles, once infected, the zoster virus persists in the body with the potential of re-emerging later in life as “shingles” (Mallick-Searle, et al., 2016; Warren-Gash, et al., 2017).  Shingles can be mild or it can cause severe, debilitating nerve pain (post herpetic neuralgia).  After the chickenpox vaccine became available in 1995, the incidence of chickenpox – and with it the risk of shingles – plummeted. Alas, there are still many of us who were born before the advent of a vaccine that would prevent chickenpox.  In the U. S., the incidence of shingles is about 1 in 100 people 60 years of age or older (CDC, 2019b; Spencer 2017). Fortunately, there are now two vaccines that can prevent shingles or reduce its severity (Shah, et al., 2019).

First Responders and Special Forces

It takes time for our immune system to respond to an invader that it has not previously encountered – e.g., a virus, bacteria, or fungus. Fortunately, our immune system has two branches:  innate immunity (first responders) and adaptive immunity (special forces). The innate immune system reacts as soon as an invader is encountered. Its sets off a nonspecific inflammatory response which attempts to surround the enemy and paint a target on its back.

The adaptive immune system takes more time to respond to the invasion. It needs to characterize the enemy and devise specific means (antibodies) to attack it. In other words, special forces need to be briefed and develop a battle plan before engaging with the enemy. This is where vaccination provides a major advantage.  If and when the enemy attempts an invasion, special forces will not need to be briefed or develop a battle plan. They already know the enemy. All they have to do is grab their gear and move out.

Live Vaccines

Live vaccines are derived from the native (wild type) infectious agent – e.g., a virus or a bacteria – that causes disease in one or more species of animal, including humans.  When rendered into a vaccine, the power of the infectious agent has been blunted (an attenuated vaccine).  Most of the punch has been taken out of it, leaving just enough to trigger an immune response.  This is the case in live-virus vaccines such as measles and chickenpox.

Sometimes a vaccine is too weak to trigger a strong immune reaction.  Hence a series of two or three vaccinations over time may be required (e.g., Hepatitis B, a virus).  For other vaccines, the body’s response is sufficient for its defenses to remember the invader for years (e.g., tetanus, a bacteria).  Once immunity begins to wane, the vaccine needs to be administered again (“booster” dose). Some viruses, however, are constantly changing (mutating) their genetic structure so that a new vaccine must be developed every year (e.g., influenza, another virus).

Although live vaccines can cause complications, they are rare.  They occur are far less frequently than do complications from the disease itself (Spencer, 2017).  For example, out of 112 children hospitalized for complications of chicken pox, thirty developed pneumonia, twenty-six developed encephalitis, thirty developed shock, and the remainder had other life-threatening complications (Cameron, et al., 2007).  Measles can also cause encephalitis (Minor, 2015).

So, if you are concerned about the risk of complications from a weakened live vaccine, consider what the wild type can do. Wild type infectious agents are unabated and fully loaded. People who decline vaccination – especially, parents of school-age children – risk the complications of the full blown disease.

The world’s population is desperately awaiting the development of a Covid-19 vaccine.  Several vaccines are in development and undergoing clinical trials (Ahn, et al., 2020; Folegatti, et al., 2020).  Hopefully, one or more will become available early in 2021.  In the meantime, be sure to get the influenza vaccine.

Last But Not Least….

There are people who cannot have even an attenuated live vaccine.  Their immune system is impaired – either by disease (immune deficient), medications (immune suppression), or otherwise immune compromised.  The very young do not have a fully developed immune system, and in the very old (frail elderly) it is waning.  Yet, if everyone around them were immunized against those infections for which we have a vaccine (herd immunity), these infectious agents would never get a foothold.  Those who are immune compromised would be sheltered from any exposure.


Ahn, D. G., Shin, H. J., Kim, M. H., et al. (2020). Current Status of Epidemiology, Diagnosis, Therapeutics, and Vaccines for Novel Coronavirus Disease 2019 (COVID-19). J Microbiology and Biotechnology, 30(3), 313–324.

Cameron, J. C., Allan, G., Johnston, F., et al. (2007). Severe complications of chickenpox in hospitalised children in the UK and Ireland. Archives of disease in childhood, 92(12), 1062–1066.

Centers for Disease Control and Prevention. (2019a.)  Chickenpox Vaccination: What Everyone Should Know.

Centers for Disease Control and Prevention. (2018.)  Measles (Rubeola).

Centers for Disease Control and Prevention. (2019b.)  Shingles (Herpes zoster).

Folegatti, P. M., Ewer, K. J., Aley, P. K.  (2020.)  Safety and immunogenicity of the ChAdOx1nCoV-19 vaccine against SARS-CoV-2: a preliminary report of a phase ½, single-blind, randomized controlled trial.  Lancet, 396(10249), 467-478.

Leung, A. K., Hon, K. L., Leong, K. F., & Sergi, C. M. (2018). Measles: a disease often forgotten but not gone. Hong Kong medical journal24(5), 512–520.

Mallick-Searle, T., Snodgrass, B., & Brant, J. M. (2016). Postherpetic neuralgia: epidemiology, pathophysiology, and pain management pharmacology. Journal of multidisciplinary healthcare9, 447–454.

Minor, P. D. (2015.)  Live attenuated vaccines: Historical successes and current challenges.  Virology, 479-480, 379-392.

Shah, R. A., Limmer, A. L., Nwannunu, C. E., et al. (2019.) Shingrix for Herpes Zoster: A Review. Skin Therapy Lett, 24(4), 5-7.

Spencer, J. P., Trondsen Pawlowski, R. H., Thomas, S. (2017.) Vaccine adverse events: Separating myth from reality. Amer Fam Physician, 95(12), 786–794.

Warren-Gash, C., Forbes, H., Breuer, J. (2017). Varicella and herpes zoster vaccine development: Lessons learned. Expert review of vaccines, 16(12), 1191–1201.