Keeping Kids Alive 

The decline of childhood mortality, beginning at the start of the 20th century, is one of the great triumphs of public health (Figure 1). Vaccines have been a key part of this history, as have improved sanitation, living conditions, nutrition, and health care. In 1900, 61.6% of childhood deaths were from infection, a proportion that declined to 2% by 1998. While much of the decline in childhood mortality pre-dated many currently used vaccines, the benefit of introducing major vaccines was quickly evident (Figures 2 and 3). For example, before vaccines, polio was a frightening infection, leaving some children with weakness and paralysis and needing support from a ventilator—an iron lung—to stay alive. There has not been a case of polio in the United States since 1979. Measles, one of the most contagious infectious diseases, was declared as eliminated in 2000 by the Centers for Disease Control and Prevention (CDC). Unfortunately, the benefits of vaccination have been reaffirmed as we now see the consequences of declining vaccination for this readily preventable disease. Measles has surged as vaccination rates have dropped, leaving pockets of vulnerable children. In 2025, there have already been 1,912 cases (through December 16) with 218 hospitalizations and 3 deaths. If the spread of measles continues through January, the US will lose its eradication status. 

Figure 1. Childhood mortality rate by age group, United States, 1900-2018

Power of Prevention 

While not the major driver of declining childhood mortality across the 20th century, vaccines have changed the face of childhood illnesses, greatly reducing the occurrence of infections that were once common (Figure 1). Take chickenpox, for example, which typically lasts 4-7 days and causes uncomfortable skin blisters, making the disease difficult for sick children and their caregivers. Although mortality from these kinds of illnesses became less and less frequent across the 20th century, they have remained a powerful cause of school absenteeism and disruption of the lives of families. Several childhood vaccines also prevent disease later in life: hepatitis and liver cancer with the hepatitis B vaccine, cervical cancer and head, throat, and neck cancers with the human papillomavirus (HPV) vaccine, and shingles with the chickenpox (varicella) vaccine.    

The past century of progress with childhood vaccines illustrates how transformative vaccines have been in preventing death and disease (Figure 1). As vaccines have increasingly become the focus of debate and their safety and necessity have become contested, it can be easy to lose sight of the significant role they have played in protecting public health.  

This commentary addresses why vaccination remains essential for protecting the health of all community members. We describe how vaccines are developed and approved, and how vaccination programs are implemented and operated to ensure that adverse consequences are detected and risks are minimal. We recognize vaccines should always be a personal choice, but we offer resources and information to help individuals make informed decisions for themselves and their families.  

Figure 2. Cases of measles per 100,000, United States, 1919-2024 

Figure 3. Cases of polio, United States, 1910-2022 

Vaccination as a Critical Public Health Tool 

Vaccines work as both a shield to protect individuals and a tool to protect communities. At the core, vaccines are a technology of containment. They protect the individual who is immunized against the worst outcomes of infection, should a person become infected. It is difficult to predict whether someone will ever encounter a vaccine-preventable disease, particularly as immunization rates have succeeded in limiting community spread. It is also hard to predict which people will recover relatively quickly from infection or be seriously affected or even killed by infection. Individuals accept a minute chance of a complication from vaccination in order to be protected against serious illness. And when entire communities are immunized, infectious diseases are unable to spread, which keeps all members safe. This “herd immunity” is important, since it is impossible for all members of a community to be immunized. Some may be too young; some may be immunocompromised; and some may have lost immune memory with age or illness. A small number of people will never develop immunity after vaccination. But if approximately 85–95 percent (depending on the infectious agent) receive a vaccine, virtually all members of the community are likely protected from infection. 

Whether vaccines are most important as a tool for individual protection or herd immunity varies based on the disease prevented. For example, the vaccine against tetanus benefits the individual, since the bacteria that causes tetanus is not contagious and the tetanus spores are ubiquitous in the environment. Disease results when the bacterium enters the body through a break in the skin, multiplies, and produces tetanus toxin that causes neurological damage and death, and is extremely difficult to treat. Vaccines have been highly effective in the US at preventing tetanus disease and death, with fewer than 40 cases in the US per year.  

Some vaccines benefit public health by protecting others in the community. For example, the vaccine against rubella provides protection for the individual who contracts the disease, but since that disease is relatively mild, protection is not essential. However, when a pregnant woman encounters rubella, her fetus can be devastated. Prior to the vaccination for rubella infection, it was the leading cause of congenital deafness and could cause congenital rubella syndrome, resulting in babies born with a range of significant health problems—intellectual disability, blindness, deafness, and death. One rubella outbreak in 1964-1965 led to an estimated 20,000 cases. Since the US adopted a strategy of universal immunization, there has been an average of 10 cases each year.   

Immunization Laws and Exemptions 

Most vaccines for children offer a mix of individual and community benefits. As such, childhood vaccination has been a cornerstone of public health for more than 50 years. The reliance on childhood vaccines to support individual and community safety and well-being relies on laws in all 50 states that require children to have proof of immunization before enrolling in schools or childcare settings. States passed these laws between 1963-1981, following the passage of the federal Vaccination Assistance Act of 1962, which provided federal support to state and local immunization programs for vaccines against polio, diphtheria, pertussis, and tetanus. By 1980, and following increases in federal funding and support, every state had a law requiring evidence of immunization for school entry. Although the federal government was heavily invested in supporting immunization, responsibility for enforcement and decisions on exemptions was squarely the state’s responsibility. Every state's law included an exemption for medical reasons, and at the time, all but two states allowed exemptions for religious or philosophical reasons. These exemptions allow children to participate in schools or childcare without evidence of immunization. Nonetheless, these mandates have been credited with maintaining high rates of vaccination. 

Vaccines are increasingly perceived as a technology for personal benefit, rather than as a community strategy, as seen by the increasing use of exemptions across the country and changes in laws to weaken mandates (Figure 4). In the 2024-2025 school year, 3.6% of children had exemptions for one or more required vaccines, an increase from 2.5% in 2019-2020. Use of exemptions varies by state, with California, which only allows exemptions for medical reasons, having the lowest rate of 0.1% while Idaho has the highest, with a rate of 15.4%. In 2025, 10 states have passed laws to allow more liberal use of exemptions or to limit the enforcement of school mandates, and Florida has announced plans to end school-based requirements but has not yet passed legislation to do so. Notably, Colorado is the only state to increase its commitment to vaccines through a 2025 law that allows vaccine mandates to be based on expert recommendations from professional organizations in addition to the CDC.  

Figure 4. Non-Medical Exemption Policies for School Immunizations  

What remains invisible in the assumption that vaccines are entirely for personal benefit is the reality that unimmunized children benefit from herd immunity. Known in public health parlance as “free riders,” these children’s parents can reject vaccines without facing significant risk of infection if they live in a community that has sufficiently high immunization rates to achieve herd immunity. As public consensus that vaccines are important erodes, concerns about whether herd immunity will remain strong enough to stave off disease grow. 

How Vaccines are Developed, Produced, Approved and Delivered  

Going from the conceptualization of a vaccine to its availability to the public is a multi-step and typically multi-year process that begins with basic science research carried out in laboratories (Figure 5). The starting point is understanding the nature of the infectious agent, its interactions with cells, and the body’s immune response to it. This understanding is critical to designing the vaccine so that the immune response blocks or weakens infection. A vaccine might involve a live, but weakened version of a virus (e.g., smallpox), an inactivated virus (e.g., the Salk polio vaccine), or critical components of the agent that may be manufactured to mimic it (e.g., the human papilloma virus (HPV) vaccines).

Figure 5. The Vaccine Life Cycle.

For example, consider SARS-CoV-2, the virus that caused the COVID-19 pandemic. The virus has spikes on its surface, as do other coronaviruses, giving rise to their name (see Figure 6). COVID vaccines target proteins on the virus’s spike, which has a key role in how the virus infects cells. The spike connects with receptors on the surfaces of cells to create a portal for entry of the virus into cells. The messenger RNA (mRNA) vaccines contain the code for the spike protein and induce cells to manufacture a critical protein component of the spike, leading to the formation of antibodies against it and thereby cutting off entry of the virus into cells. The 2023 Nobel Prize for Physiology or Medicine was awarded to Drew Weissman, M.D., Ph.D., and Katalin Karikó, Ph.D., for their foundational work on mRNA that facilitated the rapid development of the mRNA vaccines.  

Figure 6. The SARS-CoV-2

Following the initial discovery phase, the next steps involve testing the vaccine to ensure that it generates the projected immune response and to assess potential toxicity. Such testing can involve both animals in preclinical studies and people in Phase 1 and 2 investigations. Whether the vaccine works—its efficacy—is tested in so-called Phase 3 clinical trials. These studies involve randomization of people to be vaccinated or not, followed by observation to assess the rate of infection in the vaccinated and comparison or control groups. Phase 3 trials are generally large enough to be informative as to whether the vaccine offers the intended protection and causes adverse outcomes at an unacceptable frequency. They are generally not large enough to detect rare events, which are sometimes not detected until a vaccine is in use.  

Figure 5 highlights the regulatory steps in vaccine development and the involved agencies. To begin the clinical phase of vaccine development with human subjects, the Food and Drug Administration (FDA) requires companies and research teams to apply for and receive approval of an Investigational New Drug (IND) application. If the clinical trials are successful, companies can seek FDA approval through an approval process involving review of comprehensive information provided to the agency in a Biologics License Application. The FDA’s 15-member Vaccines and Related Biological Products Advisory Committee (VRBPAC) reviews the scientific data on the safety and effectiveness of vaccines and provides guidance to the FDA Commissioner, who makes the final decision concerning approval. With FDA approval, decision-making then moves to the Director of CDC who receives guidance from the members of the Advisory Committee on Immunization Practices (ACIP). Since 1964, ACIP has been charged with reviewing all available scientific data to make recommendations on how and by whom the vaccine should be used to support safe use and maximum benefit (Figure 5). ACIP work groups, traditionally comprising experts in a range of related fields, review hundreds of studies to understand how vaccines work best, when they are most effective, and when they may be contraindicated. ACIP can have up to 19 members and creates the recommended infant and childhood vaccine schedules, and then it is up to states to decide what should be required. These recommendations have an impact on some federal statutes, e.g., the Affordable Care Act, which covers ACIP-recommended vaccines, and can affect state laws for school attendance.

Once in use, there is ongoing monitoring for safety through the CDC and FDA. This process evaluates what risks may exist from a vaccine and compares them to the risk of infectious disease. For example, vaccines against COVID have a small measured increased risk of myocarditis in young people. One recent study found that over a six-month period, the vaccine caused 0.85 extra cases of myocarditis in young people compared with 2.24 extra cases from infection with COVID. In this case, the vaccine risk is tolerable in light of the significant risks that the infection presents. The takeaway message is that consideration of risk is embedded in vaccine development throughout the U.S.’s multi-step process. To be approved and used, a vaccine must be efficacious in preventing infection or limiting serious disease and pose a minimal level of risk or small risk, which is considered to be acceptable in comparison to the risks of the disease it prevents.   

Several federal programs, targeting different recipient groups, and private insurance companies, cover the cost of immunizations. For children 18 years of age and younger, ACIP-approved vaccines are funded by the CDC’s Vaccines for Children (VFC) program. Similarly, for persons receiving health care via Medicaid, vaccines approved by ACIP are covered. Medicare Part B covers vaccines for pneumococcus, influenza, COVID-19, and hepatitis B, while Part D covers other vaccines approved by the ACIP. Thus, the ACIP recommendations have sweeping implications for vaccine access in the United States.   

Monitoring the Safety of Vaccines 

A great deal of attention since the COVID-19 pandemic has focused on the process of vaccine testing and approval. Yet, less is known about the regulatory work that happens after FDA licensing and ACIP recommendations. Once a vaccine is widely distributed, there is ongoing monitoring of safety and effectiveness. Although clinical trials typically have thousands of participants, it sometimes is not until millions of people have used a vaccine that rare complications are visible. Such was the case with a rotavirus vaccine in 1999, which was removed from the market one year after licensing when it was found to cause a complication that occurred in such a small number of children that the excess was not statistically significant in the initial trial. Additionally, people in the general population have different underlying health conditions than those in clinical trials, who tend to be healthier than non-participants and may experience adverse reactions that participants do not. Ongoing monitoring also ensures vaccines are still efficacious. For example, in the 2016-2017 flu season, ACIP voted against continuing use of a specific nasal spray vaccine that data suggested was no longer effective.

Other data systems look for safety signals that a vaccine may cause adverse reactions. The Vaccine Adverse Event Reporting System (VAERS) allows doctors, patients, and family members to voluntarily submit concerns of an adverse reaction after vaccination. Although reports to VAERS are sometimes imaginative, like turning recipients into the Incredible Hulk, sometimes unlikely like having instant massive increases in penis size, or coincidental, like dying in a car accident after immunization, the system is nonetheless useful for helping to identify signals of possible adverse effects following vaccination. Other systems like the CDC’s Vaccine Safety Datalink (VSD) and the more broadly focused FDA’s Sentinel System use electronic health data from managed care organizations and insurers to study patterns between vaccine administration and subsequent medical care. Researchers can use these data to examine the plausibility of reports made to VAERS or look for other signals that a vaccine may cause complications not yet identified, including in individuals with particular underlying health conditions.  

When an adverse reaction does occur, individuals are eligible for compensation through the federal Vaccine Injury Compensation Program. Established by Congress in 1986 with the passage of the National Childhood Vaccine Injury Act, this claims court compensates people who are harmed by a vaccine from a fund that is supported with a seventy-five-cent tax on every vaccine administered. This system was created after parents began suing vaccine manufacturers for complications they saw as resulting from the no-longer administered whole-cell pertussis vaccine. These lawsuits resulted in some companies withdrawing from the market. Fearing that the US would no longer have adequate supplies of vaccines, Congress created this system and provided protection against liability to manufacturers. Although the system was established for childhood vaccines, most people receiving compensation today are adults, with complications from influenza vaccination being the most common claim. From the start of the court in 1988 through September 2025, 12,225 claimants have been compensated. In this same time period, an estimated 5 billion doses of vaccines were administered.  

Vaccines and Vaccination in the Current U.S. Administration 

Politics have long intersected with public health, affecting funding, policies, and actions, but politicization of public health has arguably never been so extreme as now. Polls show that trust in health agencies and public health dropped during and following COVID. A KFF tracking poll showed a decline in trust in key agencies—the Department of Health and Human Services (DHHS), the CDC, and the FDA—comparing January 2025 to June 2023. In 2023, levels were lower among Republicans and declined more than among Democrats. The transition from the Biden to the Trump Administration has eroded confidence in public health institutions more broadly and vaccines specifically across the political spectrum.  

As the first year of the second Trump Administration comes to a close, the stance of critical agencies towards vaccines has profoundly changed. Robert F. Kennedy Jr, Secretary of the Department of Health and Human Services, has long been critical of vaccines. Appointees he has made to key positions and committees have tended to reflect the Secretary’s positions on vaccines and evidence-based decision-making. Changes in the membership of the ACIP are exemplary and concerning. In June 2025, Secretary Kennedy dismissed all 17 voting members of ACIP and replaced them (to date) with 12 individuals who have limited expertise related to vaccines and public health, and some have known anti-vaccination biases. An evaluation of the performance of the new ACIP by its former members documented a lack of understanding of procedures and of vaccine science. This move is currently the subject of ongoing litigation in the case of American Academy of Pediatrics v. Robert F. Kennedy, Jr., which was filed by the American Academy of Pediatrics (AAP), American College of Physicians (ACP), American Public Health Association (APHA), Infectious Diseases Society of America (IDSA), Massachusetts Public Health Alliance (MPHA), Society for Maternal-Fetal Medicine (SMFM), and a pregnant physician.  

Most recently, the CDC website has been changed to state that vaccines might cause autism, replacing language stating that scientific evidence does not show a link between vaccines and autism. The speculation that vaccines might cause autism dates to a 1998 publication in The Lancet based on findings in 12 children. Twelve years later, the paper was formally retracted because of falsities and the revelation that the lead author was involved in litigation around vaccines and thus had a clear conflict of interest. That same year, the lead author was banned from practicing medicine in Great Britain. Since then, more than a dozen large studies have shown no relationship between autism and vaccines. Despite the dubious origins of a link between vaccines and autism and the strong countering evidence of no link, fervent belief by some in a causal role of vaccines in causing autism remains. 

During the first Trump Administration, Operation Warp Speed delivered efficacious vaccines for SARS-CoV-2 with spectacular rapidity, saving countless lives.  The mRNA vaccine technology provided a platform for rapid vaccine development and for tailoring vaccines as new variants developed. However, under Secretary Kennedy, the Biomedical Advanced Research and Development Authority (BARDA) ended 22 vaccine projects, nearly $500 million in funding, because the Secretary stated that: “…the data show these vaccines fail to protect effectively against upper respiratory infections like COVID and flu.” He explained his opposition to mRNA vaccines specifically noting, “We’re shifting that funding toward safer, broader vaccine platforms that remain effective even as viruses mutate.” In fact, the mRNA technology works well for quickly changing vaccines as infectious agents mutate. Kennedy’s position reflects distrust of the technology that advanced during COVID and overlooks promising research that is identifying how the technology can treat cancer and other diseases.    

Other changes at the federal level may further undermine confidence in vaccines and weaken the ability of public health agencies to respond to the next possible pandemic. Estimates are that the CDC’s workforce has been reduced by one-third between January and October 2025. This is a significant limitation since disease surveillance and responses rely on these workers. The United States’ withdrawal from the World Health Organization has concerning consequences around vaccination, reducing access to epidemiological data, pathogen samples, and the genetic sequences of pathogens, which are critical to vaccine development. In more pedestrian ways, vaccine safety monitoring relies on expert advisors who can understand minute safety signals and analyze and interpret complex data. This monitoring supports vaccine confidence and ensures that payors can provide people with an accessible range of vaccine choices.

Summary  

Vaccines work and protect the health of populations and people. One deadly disease—smallpox—has been eliminated through a global vaccination program. In the United States, vaccines are developed through rigorous scientific and regulatory processes to maximize benefit and minimize risks. Vaccines can have adverse effects, and watchful monitoring is in place to detect them. We worry that the current politicization of vaccines and falling rates of vaccination will lead to outbreaks of vaccine-preventable disease, as is happening now with measles. We urge people seeking information about vaccines, whether for their children or themselves, to use trustworthy sources.   

Resources 

American Academy of Pediatrics: The AAP’s Immunization website highlights their vaccine recommendations as well as the science informing them. Interactive vaccination maps highlight state-level vaccination rates as well as exemptions. The AAP also provides parent-centered resources at Healthychildren.org. 

Colorado Department of Public Health & Environment: CDPHE provides general vaccine information, state level school vaccination requirements, and vaccine clinic information. CDPHE also has an interactive vaccination data portal where users can view vaccination data for different school-age categories as well as interactive maps. 

Immunize Colorado: Immunize Colorado is a non-profit promoting vaccine uptake and equity. In addition to providing resources for the general public, Immunize Colorado also sponsors free and low-cost vaccination clinics throughout the state. 

Written in collaboration with Dr. Jennifer Reich, Professor of Sociology at the University of Colorado, Denver.

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This article is part of a regular column, The Jon Samet Report, on the biggest issues facing us today in public health. It is written and curated by the former dean of the Colorado School of Public Health, Jon Samet, a pulmonary physician and epidemiologist, and Professor of Epidemiology and Occupational and Environmental Health, and his colleagues. Dr. Samet is a global health leader, shaping the science and conversation on issues ranging from tobacco control to air pollution to chronic disease prevention and more. Each installment shares expert insights on public health issues from local to global.