I probably don’t need to convince any regular readers of Science-Based Medicine that childhood immunizations provide substantial benefit to the children receiving them and society in general. While there aren’t any people still around today that experienced life before our earliest discoveries in vaccine science at the close of the 18th century, there are many that saw the advent of widespread public health efforts taking advantage of advances in our ability to mass produce safe and effective vaccines, starting with smallpox, diphtheria, pertussis, and tetanus prevention in the late 1940s. Over the following decades, many additional vaccines have been developed that have saved lives, prevented untold suffering, and improved the lives of billions of people.

Routine childhood immunizations have changed the world for the better in seemingly incalculable ways. We know this indisputable fact to be true. Despite this, the anti-vaccine movement has become increasingly vocal in recent years, buoyed by a rising tide of anti-science misinformation and even targeted disinformation inspired by the SARS-CoV-2 pandemic in certain segments of the population. In an effort to push back against measures designed to reduce the risk of serious COVID-19 cases, established vaccines are also taking a hit with even polio poised to make a comeback in the United States.

Though some of our vaccines work better than others (flu shot, I’m looking in your direction), they work even if people don’t believe in them. As I said above, this is an undeniable truth at this point. While there is no perfect medical intervention with zero risk, the entirety of the current childhood vaccine schedule is absurdly safe and effective. But a lack of belief in vaccines certainly interferes with a key aspect of their disease prevention capabilities, namely getting shots in arms, or drops in mouths in some cases.

While I don’t think that any new data is likely to convince large numbers of anti-vaccine holdouts, perhaps there are still a few vaccine hesitant parents out there whose minds can be changed. In that effort, it is always nice to have updated information on just how effective childhood immunizations are. Today I will discuss just that.

Impact of routine childhood immunization in reducing vaccine-preventable diseases in the United States

Earlier this month, a paper with the above title was published in Pediatrics that investigated the public health impact of childhood vaccines in the United States using 2019 population data. The authors presented updated estimates of disease incidence with and without pediatric vaccines currently recommended for children 10-years-old and younger to prevent 14 different diseases. Though there are few limitations inherent in this kind of analysis, even if their conclusions are a bit of an overestimation the results would still be impressive.

Earlier published data on the benefit of childhood vaccines is plentiful. The authors point out that vaccines given between 1994 and 2013 prevented an estimated 21 million hospitalizations, 732,000 deaths, and 322 million cases of disease in the United States. In the past 15 years or so, however, there have been additions to the vaccine schedule that are less represented in the available literature, something this new paper looks to remedy:

This study updates estimates of the reduction in overall and age-specific disease incidence associated with the routine childhood immunization program in the United States (based on the 2017 to 2021 vaccination schedule). This update incorporates changes in vaccine utilization rates and observed incidence of the targeted vaccine-preventable diseases since previous evaluations.

I will briefly describe each of the 14 vaccine-preventable diseases targeted in the current schedule for young children and reveal the updated case prevention estimates.

Diphtheria

Diphtheria is a bacterial infection of the upper respiratory system, and sometimes skin, that is spread just like a common cold. Unlike a common cold, however, the toxin produced by this particular strain of bacteria can cause severe tissue damage resulting in airway obstruction, cardiac injury, muscle weakness, and even paralysis. With appropriate treatment, 5-10% of children still die from this condition.

  • Percent reduction of disease in the vaccine era: 100%
  • Prevaccine incidence per 100,000: 600
  • 2019 cases without immunization: 263,000
  • 2019 cases with immunization: <1
  • Cases prevented: 263,000

Hepatitis A

Hepatitis A is a highly contagious viral infection that targets the liver. Unlike Hepatitis B and C, it is usually spread via contaminated food or water and can also move rapidly through groups of young children who are not exactly known for practicing good hand hygiene. While not likely to cause chronic disease that requires a liver transplant, it can cause serious injury with severe symptoms that last for weeks to months and there is no effective treatment that shortens the illness severity or duration.

  • Percent reduction of disease in the vaccine era: ~87%
  • Prevaccine incidence per 100,000: 17
  • 2019 cases without immunization: 56,000
  • 2019 cases with immunization: 7,000
  • Cases prevented: 49,000

Hepatitis B

Hepatitis B is another viral infection that targets the liver, but is spread via contaminated blood, semen, or other body fluids such as vaginal secretions during childbirth. Though most adults will have a self-limited course, in children, and particularly in infants, it is likely to cause chronic liver disease and cirrhosis of the liver. Liver transplant is ultimately necessary in some cases. Chronic infection can also result in the development of liver cancer, meaning that before there was an HPV vaccine the hepatitis B vaccine had been preventing cancer for decades.

  • Percent reduction of disease in the vaccine era: ~86%
  • Prevaccine incidence per 100,000: 46
  • 2019 cases without immunization: 150,000
  • 2019 cases with immunization: 22,000
  • Cases prevented: 128,000

Haemophilus influenzae type b

Haemophilus influenzae type B, commonly called Hib, is bacteria that was a common cause of ear infections and pneumonia but is infamous for its ability to cause a severe form of meningitis and a dangerous infection of the epiglottis. Every pediatrician practicing medicine in the 1980s or earlier had patients hospitalized because of this common infection, a scary percentage of which died or had long lasting neurological injuries. In my roughly 20 years of practice, I have never seen a case.

  • Percent reduction of disease in the vaccine era: ~100%
  • Prevaccine incidence per 100,000: 92
  • 2019 cases without immunization: 18,000
  • 2019 cases with immunization: <100
  • Cases prevented: 18,000

Influenza

It’s the flu. You know this one. A typical case of the flu can be rough in healthy adults and even the vast majority of kids, but it can cause severe disease in the immune compromised, people with underlying cardiac or respiratory diseases, and the very young. There are a number of potential non-respiratory sequelae attributed to the flu, such as Guillain-Barré syndrome and acute disseminated encephalomyelitis, and huge economic costs as well.

  • Percent reduction of disease in the vaccine era: ~17%
  • Prevaccine incidence per 100,000: 1,232
  • 2019 cases without immunization: 7,115,000
  • 2019 cases with immunization: 5,879,000
  • Cases prevented: 1,236,000

Measles

The measles is an extremely contagious viral upper and potentially lower respiratory infection that unfortunately has a predilection for causing inflammation of the brain and is fatal in about 1-2 out of every 1,000 cases. It can also cause an uncommon but always fatal disease called subacute sclerosing panencephalitis that can emerge years after an even mild case of measles.

  • Percent reduction of disease in the vaccine era: ~100%
  • Prevaccine incidence per 100,000: 2,129
  • 2019 cases without immunization: 3,639,000
  • 2019 cases with immunization: <1,000
  • Cases prevented: 3,639,000

Mumps

Mumps is another viral infection that was once incredibly common prior to the MMR vaccine. It causes inflammation and swelling of salivary glands in the face but can also cause injury to the testicles that can result in infertility. It is also a potential cause of inflammation of the brain and can cause deafness.

  • Percent reduction of disease in the vaccine era: ~100%
  • Prevaccine incidence per 100,000: 1,312
  • 2019 cases without immunization: 2,243,000
  • 2019 cases with immunization: 3,000
  • Cases prevented: 2,240,000

Rubella

Rubella, another highly contagious viral infection, is usually a mild or even asymptomatic infection. If you happen to be a fetus whose mother is infected during the first 3 months of pregnancy, however, it is a very different story. In that case, there is a 90% chance of developing congenital rubella syndrome, which is a serious disease potentially injuring the brain, heart, and eyes. Rubella, along with measles and polio, are considered eliminated in the United States as defined by the World Health Organization. I’ve never personally seen a case of any of them, though I’m worried that won’t last.

  • Percent reduction of disease in the vaccine era: ~100%
  • Prevaccine incidence per 100,000: 1,124
  • 2019 cases without immunization: 1,921,000
  • 2019 cases with immunization: <10
  • Cases prevented: 1,921,000

Pertussis

Pertussis, more commonly known as whooping cough, is a highly contagious bacterial infection of the upper and lower airway that is terrible in adults and deadly in infants. About a third of infants with pertussis will require hospitalization and about 1% of them will die. Though known as a respiratory disease, it can cause inflammation of the brain in young patients.

Okay, the current pertussis vaccine certainly isn’t the poster child for our vaccine schedule. Because of an unfortunate reaction to fear of bogus neurological side effects heavily promoted by an infamous 1982 anti-vaccine documentary, and a subsequent drop in acceptance of the vaccine by parents, we changed from whole cell vaccine to an acellular version which, while good, is just not as effective as the original vaccine. It doesn’t provide as much protection and immunity wanes (as does immunity from infection) so boosters are needed throughout adulthood. As a result, we see a fair amount of pertussis these days.

  • Percent reduction of disease in the vaccine era: ~91%
  • Prevaccine incidence per 100,000: 744
  • 2019 cases without immunization: 2,442,000
  • 2019 cases with immunization: 217,000
  • Cases prevented: 2,225,000

Streptococcus pneumoniae

Pneumococcus is the leading cause of ear infections and pneumonia but is also a well-known cause of bloodstream infections, meningitis, and much more. It has killed countless millions of children and adults historically and still to this day kills more than 300,000 children under the age of five around the world every year, largely because of disparities in vaccine availability. Thanks to increasingly effective vaccines that cover more and more strains of this bacteria, the incidence has plummeted in the United States.

Though there was an earlier version for older adults, pediatricians just a few years older than me would have seen a lot of severe pneumococcal disease because the first vaccine for children didn’t roll out until 2000. As I mentioned above, since then the vaccine has been updated with additional strains and better protection. I still see suspected pneumococcal pneumonia and ear infections, but I haven’t seen a case of invasive pneumococcal disease (IPD) such as meningitis, sepsis, or even a positive blood culture in years.

  • Percent reduction of disease in the vaccine era: ~60% (IPD only)
  • Prevaccine incidence per 100,000: 24 (IPD), 152 (hospitalizations)
  • 2019 cases without immunization: 79,000 (IPD), 500,000 (hospitalizations)
  • 2019 cases with immunization: 31,000 (IPD), 78,000 (hospitalizations)
  • Cases prevented: 48,000 (IPD), 422,000 (hospitalizations)

Polio

Polio is a viral infection that can cause flu-like illness but is best known for complications like muscle weakness than can progress to paralysis and the need for lifelong mechanical ventilation such as the iron lung. The early days of the SARS-CoV-2 pandemic actually inspired some innovation in this outdated form of negative pressure ventilation, so we may see an updated version in use in the future. The last case of naturally occurring polio in the United States was diagnosed in 1979.

  • Percent reduction of disease in the vaccine era: ~100%
  • Prevaccine incidence per 100,000: 21
  • 2019 cases without immunization: 70,000
  • 2019 cases with immunization: 0
  • Cases prevented: 70,000

Rotavirus

This is a blast from the past. Rotavirus is a very contagious viral cause of gastroenteritis famous for its distinctively stinky diarrhea, and it used to send a lot of kids to the ED and put a lot in the hospital. I haven’t seen a case since residency because widespread use of a safe and effective vaccine began right after I finished in 2006. In addition to infection with this nasty little virus, it looks increasingly likely that this vaccine also prevents the development of diabetes in a lot of kids.

The history of rotavirus vaccines is fascinating and serves as a compelling counterpoint to claims that vaccines aren’t safe and there is a conspiracy involving Big Pharma and Uncle Sam. Soon after the approval of an earlier vaccine, a rare side effect was picked up with appropriate use of VAERS data and it was recalled within a year. More research was done and safer versions eventually came out. All vaccines are subject to this degree of monitoring.

  • Percent reduction of disease in the vaccine era: ~91%
  • Prevaccine incidence per 100,000: 340 (hospitalizations), 1,072 (ED visits)
  • 2019 cases without immunization: 67,000 (hospitalizations), 210,000 (ED visits)
  • 2019 cases with immunization: 6,000 (hospitalizations), 82,000 (ED visits)
  • Cases prevented: 61,000 (hospitalizations), 128,000 (ED visits)

Tetanus

Tetanus holds the distinction of being the only vaccine-preventable illness that is infectious but not contagious. It is an uncommon but always serious and often fatal infection that occurs when a wound is contaminated with a certain bacteria found in soil. In the anaerobic conditions of a deep wound, the bacteria produces a toxin which results in uncontrolled muscle spasm and rigidity throughout the body. It is a terrible way to go.

  • Percent reduction of disease in the vaccine era: ~98%
  • Prevaccine incidence per 100,000: <1
  • 2019 cases without immunization: 1,000
  • 2019 cases with immunization: <100
  • Cases prevented: 1,000

Varicella

Last but not least is varicella, more commonly known as chicken pox. This same virus, which lies dormant in the brain, can recur years later as shingles. There is a vaccine for that too, but it isn’t recommended until age 50. I had chicken pox in 1983, and many readers likely did as well in their childhood, unless they were born after 1995. In young children who aren’t freshly born, while it certainly isn’t fun, it is more of an economic burden than a cause of severe or deadly disease. That changes for teens and adults or in the context of a compromised immune system, as primary infection is much more likely to lead to pulmonary disease and dangerous inflammation of the brain.

  • Percent reduction of disease in the vaccine era: ~98%
  • Prevaccine incidence per 100,000: 1,328
  • 2019 cases without immunization: 4,359,000
  • 2019 cases with immunization: 97,000
  • Cases prevented: 4,262,000

Conclusion: the data speaks for itself

When you add all this up, the authors concluded that the current childhood immunization schedule for kids 10 and younger prevented roughly 24 million cases of disease in 2019 and likely every other year as well. There are 6 horrible afflictions now with an incidence of less than one case per every 100,000 people in the United States. And hospitalizations are dramatically reduced even for diseases with vaccines that aren’t quite as effective. Of course this all falls apart if vaccine rates in children decrease, even by just a few percentage points with diseases as contagious as measles.

As I mentioned earlier, there were some limitations to this analysis. It’s complicated stuff. First off, some credit for decreasing incidence rates historically does go to improved sanitation/hygiene, healthcare access, and general standards of medical care. Some also goes to booster doses of certain vaccines given to adolescent and adult patients.

Another problem with this data is that is that it presumes an even distribution of vaccine benefit. Sadly, that just isn’t the case as there is significant disparity when it comes to different racial and ethnic groups. Disease burden is often shifted towards groups of people who, for a variety of economic and cultural reasons, are less likely to receive what would be standard of care for the white and relatively wealthy. This has been painfully apparent during the current pandemic with deaths and morbidity heavily shifted towards people of color.

There are other reasons why this data is unavoidable a little sloppy, such as the assumption that the disease burden of vaccine-preventable illnesses is steady from year to year. We know that some diseases can have significant variation. It also may be painting too rosy a picture as it reflects data from before the SARS-CoV-2 pandemic, which has negatively impacted vaccine rates.

This isn’t exact data. It would be virtually impossible to make that happen. It probably overestimates the benefit of vaccines a bit, but I highly doubt that it is clinically meaningful. This study, even with the limitations, adds additional compelling evidence that vaccines are the single greatest advance in medical science at the top of an already rather large pile.

Author

  • Clay Jones, M.D. is a pediatrician and a regular contributor to the Science-Based Medicine blog. He primarily cares for healthy newborns and hospitalized children, and devotes his full time to educating pediatric residents and medical students. Dr. Jones first became aware of and interested in the incursion of pseudoscience into his chosen profession while completing his pediatric residency at Vanderbilt Children’s Hospital a decade ago. He has since focused his efforts on teaching the application of critical thinking and scientific skepticism to the practice of pediatric medicine. Dr. Jones has no conflicts of interest to disclose and no ties to the pharmaceutical industry. He can be found on Twitter as @SBMPediatrics and is the co-host of The Prism Podcast with fellow SBM contributor Grant Ritchey. The comments expressed by Dr. Jones are his own and do not represent the views or opinions of Newton-Wellesley Hospital or its administration.

Posted by Clay Jones

Clay Jones, M.D. is a pediatrician and a regular contributor to the Science-Based Medicine blog. He primarily cares for healthy newborns and hospitalized children, and devotes his full time to educating pediatric residents and medical students. Dr. Jones first became aware of and interested in the incursion of pseudoscience into his chosen profession while completing his pediatric residency at Vanderbilt Children’s Hospital a decade ago. He has since focused his efforts on teaching the application of critical thinking and scientific skepticism to the practice of pediatric medicine. Dr. Jones has no conflicts of interest to disclose and no ties to the pharmaceutical industry. He can be found on Twitter as @SBMPediatrics and is the co-host of The Prism Podcast with fellow SBM contributor Grant Ritchey. The comments expressed by Dr. Jones are his own and do not represent the views or opinions of Newton-Wellesley Hospital or its administration.