Peter H Gilligan, Ph.D., D(ABMM) emeritus and F(AAM) was a medical microbiologist at UNC Health for 35 years. Here, he reflects on the value of vaccines observed throughout his lifetime.
One of my earliest inspirations for becoming a microbiologist was reading when I was 12 years old about Louis Pasteur's experiments with an anthrax vaccine and, subsequently, his courage-or perhaps, foolhardiness-in giving an experimental rabies vaccine to a child named Joseph Meister (who had been bitten by a rabid dog) and saving his life.
Ask yourself the following questions:
- Have you ever received a smallpox vaccination?
- Do you know someone who had polio, whooping cough (pertussis), tetanus or measles?
- Can you look at a Gram stain of a cerebrospinal fluid and predict a child's future?
- Have you ever been on a college campus when an outbreak of meningococcus occurred?
- Do you get COVID-19 and influenza vaccines each year?
I can answer "Yes" to all of these questions and look to these examples as a template that points to the power of vaccines.
Smallpox Vaccination
My initial vaccination against smallpox likely occurred before I entered kindergarten in 1956. Then, in 1968, when I traveled to England on a high school field trip, I had to show recent smallpox vaccination to enter the U.K. One of my lasting memories as a teenager is of my father, a rural general practitioner, administering the vaccine by multiple punctures with a bifurcated needle. This tool played a critical role in global smallpox eradication, which was accomplished in 1977. However, the story did not end there.
In 2001, following 9/11 and a series of deadly anthrax attacks, the world turned a scrutinizing eye toward terrorism of all kinds. Bioterrorism experts recommended preparing for the possibility of a smallpox attack, based on the infectious agent's previous use as a biological weapon. As a precaution, select health care providers were vaccinated against smallpox. It was the first time smallpox vaccines had been administered in the U.S. since 1972. That threat has faded, and, due to eradication of the disease, no one should fear this terrible pathogen.
Polio Vaccination
The inactivated polio vaccine was first introduced in 1955, with a live attenuated vaccine to follow in the early 1960s. It was too late for my sister-in-law and her cousins who contracted the disease. Fortunately, they had mild cases. Others were not so lucky, requiring long-term support with iron lungs or being permanently paralyzed.
Since that time, thanks to the incredible power of vaccines, polio has been eliminated from most parts of the world. Pockets of polio persist, primarily in areas of conflict, where heroic vaccinators risk their lives to protect children from the devastating effects of the disease. Until global polio eradication by vaccination is complete, it is prudent that vaccination with inactivated polio vaccine continues around the world, including in countries, like the U.S., where the disease has been eliminated.
Measles-Mumps-Rubella (MMR) Vaccination
A live, attenuated measles vaccine was first licensed in 1963 by investigators at Boston Children's Hospital. It was too late for me, as I had measles in the late 1950s, a time when there were an estimated 500,000 cases of measles annually. By 1973, 3 live attenuated vaccines for measles, mumps and rubella were combined into the vaccine known today as MMR. With the introduction of MMR (and its widespread use) annual cases of measles, one of the most contagious of all infectious diseases, plummeted from hundreds of thousands to dozens.
However, as vaccine refusal has become more widespread, a worrying trend is developing. Cases of measles have slowly risen, with 42 U.S. cases in 2023 rising to 285 in 2024. As of April 1, 2025, there was an ongoing outbreak of measles in the Southwestern U.S., with the epicenter in West Texas consisting of 417/422 cases occurring in individuals who were unvaccinated or had an unknown vaccination status. The epicenter of this epidemic was Gaines County, which had a high rate of unvaccinated children. Tragically, one unvaccinated child died. At the time this article was written, an additional 48 cases had been reported from a bordering region of New Mexico where an unvaccinated adult also died, as well as 9 cases in Oklahoma and 23 in southwestern Kansas.
A common theme in the 2025 outbreak is that over 90% of cases have occurred in individuals who are unvaccinated or in whom vaccination status is unknown. The decreasing MMR vaccination rates in the past 5 years may represent a tipping point presaging much higher numbers of measle cases in the coming years if MMR vaccination rates continue to decline.
Diphtheria, Pertussis and Tetanus (DPT) Vaccination
Both diphtheria and tetanus have been rare diseases throughout my lifetime. However, in the late 1950s, the small town where I grew up was touched by tetanus when one of our neighbors died from the disease.
Pursuit of a safe and effective pertussis (whooping cough) vaccine has involved decades of ups and downs. It is a fascinating story, covered in detail in an article I wrote in Oct. 2022. Unfortunately, recent trends in pertussis cases are even more concerning than those being observed for measles. Over 35,000 cases of pertussis were reported in 2024, the highest number in decades. A decline in DPT vaccination is, once again, associated with the increased number of cases.
Haemophilus influenzae type B or Streptococcus pneumoniae
A colleague's 6-year-old son was asked in school what his pathologist father did for a living. The boy replied, "He looks in a microscope and predicts the person's future."
In the early part of my career in the 1980s, I worked in a children's hospital, where we annually saw approximately 30-50 children under the age of 5 with invasive disease due to encapsulated Haemophilus influenzae type B or Streptococcus pneumoniae. The most feared complication of both was bacterial meningitis, which has a mortality of 15% for H. influenzae type B and 17% for S. pneumoniae in this age group.
When I saw a cerebrospinal fluid (CSF) Gram stain that looked like the figure below, I sadly knew that the child would likely die or be significantly to profoundly neurologically impaired for life-a tragedy. A normal CSF Gram stain has no white blood cells (WBCs) (the large, pink bodies) or bacteria (the smaller purple bodies) present. When I looked at Gram stains of normal CSF specimens, I literally saw nothing in the microscope. However, when bacteria invade the central nervous system, a profound inflammatory reaction occurs, which involves recruitment of WBCs to help fight the infection. Unfortunately, both H. influenzae type B and S. pneumoniae are encapsulated, meaning they are surrounded by an outer layer of polysaccharide called a capsule, which protects them from being killed by WBCs. As a result, the inflammatory response intensifies, resulting in swelling of the brain. If left unchecked by antimicrobial therapy, it results in death or life-long neurologic impairment.
The good news is that conjugate vaccines against each of these organisms were developed. Conjugated H. influenzae type b vaccine became available in 1987, while a conjugated S. pneumoniae vaccine became available in 2000. From 2000 until my retirement in 2019, I saw fewer than 5 Gram stains like the one above-the same number I typically saw in a 3-6-month span in the 1980s. An additional benefit is invasive infections due to S. pneumoniae declined in adults as their vaccinated children or grandchildren no longer spread the organism to them.
Campus Outbreaks of Neisseria meningitidis
I have been associated with the University of North Carolina for 40 years. The University mandates specific vaccinations prior to matriculation, including polio, MMR and DPT. Still, the vaccine for which I am most grateful is the conjugated Neisseria meningitidis vaccine. The newest meningococcal vaccine, approved in 2023, protects against all 5 serogroups. This is important because there was no vaccine against serogroup B when, in 2005, a student at UNC with meningoccemia presented to our student health department. The individual was able to give a fairly complete history, which included attending a party that was attended by somewhere between 500-1000 college students from different colleges and universities a few days before, as well as attending a lecture with approximately 300 other students immediately prior to presenting to student health.
This became a major public health issue across multiple campuses. With worried parents calling the university, the decision was made to provide prophylactic ciprofloxacin to the 300 students who thought they were "exposed," although according to the U.S. Centers for Disease Control and Prevention (CDC), only a handful meet the criteria for exposure. Fortunately, there were no secondary cases.
Recent reports of ciprofloxacin resistant N. meningitidis in North Carolina make the antibiotic less useful in controlling outbreaks and point to the value of prevention. Using the new pentavalent vaccine to prevent potential outbreaks is a more prudent measure.
How Effective Are the Influenza and COVID Vaccines?
Flu (influenza) shots are administered in the Northern Hemisphere in late September-early October because we understand that immunity only lasts for ~6 months. Yes, people sometimes get flu-like symptoms from the shot: arm pain, mild malaise or low-grade fevers. Although inconvenient, it is a small price to pay because we know these symptoms indicate the immune system is building immune protection and will keep us safe. Data suggest that the influenza vaccine is only modestly effective in preventing influenza infections. However, vaccinated individuals who become infected have milder disease and are much less likely to be hospitalized than unvaccinated people.
The decision to cancel, without explanation, the March 13, 2025 FDA meeting, during which an advisory committee would have determined the composition of the 2025-26 flu vaccine has caused concern in the microbiology and infectious disease communities. This guidance is essential to the manufacture of the flu vaccine, which requires 6 months. It is unclear if the vaccine production will be delayed, since the vaccine is typically based on guidance from the World Health Organization (WHO), which determines vaccine composition on influenza disease activity in the Southern Hemisphere.
In fall of 2024, my wife and I got our 7th COVID-19 vaccine-even though we each have had separate, symptomatic COVID-19 infections in the past 2 years. In addition, I had an asymptomatic infection at the time of my wife's symptomatic one, which I learned by completing a home test. Upon reading that positive result, I followed the existing CDC guidelines and stayed home for 5 days, so that I would not expose others. Newer CDC guidelines do not directly address asymptomatic infections, but I am comfortable with the older guidance.
Why did we choose to get vaccinated again? COVID-19 vaccines do 2 very important things: reduce the likelihood of being hospitalized and of dying from COVID-19. Like influenza, vaccine protection is limited to ~6 months, and new antigenic variants can emerge, limiting the vaccine's effectiveness. Therefore, it is essential that those at risk, especially immunocompromised, and those over age 65 get COVID-19 boosters.
What Action Does My Family Take?
When our children were young, in consultation with their pediatrician, they received all CDC recommended vaccinations. My wife and I, both health care professionals, receive all CDC recommended vaccines, as well. Given the limitations of the COVID-19 and flu vaccines, we accept that we will need to continue to receive both vaccines in the fall of each year.
Final Thoughts
My wife and I have dedicated our lives to combating infectious diseases. When my wife, a virologist and infectious disease doctor, first started caring for HIV-infected people in 1982, their life expectancy was measured in weeks to months. Today, due to the miracle of anti-viral treatments, people living with HIV can expect to live a near-normal lifespan if they are compliant with their HIV therapies. As a microbiologist, I have seen another modern-day miracle, vaccines, lead to the disappearance of a variety of infectious diseases, only to have some, measles and pertussis, begin to re-emerge because of decisions not to have children vaccinated. These pathogens can kill: 2 measles deaths in the current outbreak and 2 deaths per 100 infants with pertussis. Protect the ones you love and yourself; get recommended vaccines.
Many people have questions or misconceptions about how vaccines work. Explore ASM's content on the science behind vaccines.
