How Vaccines Changed the World

 Introduction

Vaccination campaigns are widely considered to be a public health success story. Since Edward Jenner pioneered the smallpox vaccine in the 1700s, they’ve significantly reduced disease rates around the world and are credited with saving millions of lives—primarily in low- and middle-income countries. 

In the years following the COVID-19 pandemic, there’s been a rise in vaccine naysayers and a consequential uptick in disease outbreaks; misinformation about side effects is a root cause, experts say. Even in countries with low communicable disease rates, illnesses are getting harder to protect against as people opt out of vaccinations. Another major challenge is the geopolitical inequity of wealthy countries being the main producers but slow to disburse doses. Health experts say that for vaccines to do their job, countries need to bolster their efforts to counter disinformation and prioritize support to low-income countries that are battling diseases—from production to distribution. Meanwhile, in the United States, the new head of health policy, Robert F. Kennedy Jr. (RFK) is signaling a shift away from a history of having vaccines squarely on the U.S. public health agenda.

How do vaccines work?

There are currently vaccines to prevent at least twenty-five threatening diseases worldwide, according to the World Health Organization (WHO), the UN health agency. Vaccinations train the body to build antibodies, which are proteins produced by the immune system to fight illness. They contain weakened or inactive parts of a pathogen (known as an antigen) that triggers an immune response within the body, so it can recognize when it encounters the disease and shut it down. 

Some vaccines are important for “herd immunity,” meaning that if almost all of a population is vaccinated, the disease cannot circulate as easily. This is especially critical for people who are not able to get vaccinated, such as those who have a weakened immune system, are pregnant, or are too young or old for it to be safe.

Who oversees vaccine development and deployment?

The bodies that steer vaccine use and development are country-specific. National regulatory agencies have the final word on whether a vaccine can be used in a country’s borders; in the United States, that’s the Food and Drug Administration (FDA). Generally, the process follows a path along the lines of: research and discovery, testing, manufacturing, approving, recommending for use, and monitoring safety after approval. 

The Vaccine Production Process

Developing a vaccine generally takes 5 to 10 years or longer, although the timeline can be compressed, as it was for COVID-19 vaccines.

Preclinical R&D

1–5 years

Vaccine candidates identified in lab and tested to determine

their stability, toxicity and safety for use in humans

Phase 1 clinical trials

Testing in a small group (up to several dozen people) to determine a dose with an acceptable level of safety and preliminary estimate of biological and pharmacological effects

Phase 2 clinical trials

Testing in a larger group (up to several hundred people) to generate preliminary estimate of immunogenicity, safety, dose tolerability, and potential adverse effects

5–8 years

Phase 3 clinical trials

Testing in a larger group (tens of thousands of people) to provide a more definitive answer on the safety and efficacy of the intervention, often in randomized trials involving a known comparator product (a control)

Approval

0.5–2 years

Regulatory agency reviews

Manufacturing

Vaccine production facilities inspected and scaled up

Distribution

Vaccines distributed to health care providers and made

available to the public

Developing a vaccine generally takes 5 to 10 years or longer, although the timeline can be compressed, as it was for COVID-19 vaccines.

Preclinical R&D

1–5 years

Vaccine candidates identified in lab and tested to determine

their stability, toxicity and safety for use in humans

Phase 1 clinical trials

Testing in a small group (up to several dozen people) to determine a dose with an acceptable level of safety and preliminary estimate of biological and pharmacological effects

Phase 2 clinical trials

Testing in a larger group (up to several hundred people) to generate preliminary estimate of immunogenicity, safety, dose tolerability, and potential adverse effects

5–8 years

Phase 3 clinical trials

Testing in a larger group (tens of thousands of people) to provide a more definitive answer on the safety and efficacy of the intervention, often in randomized trials involving a known comparator product (a control)

Approval

0.5–2 years

Regulatory agency reviews

Manufacturing

Vaccine production facilities inspected and scaled up

Distribution

Vaccines distributed to health care providers and made

available to the public

Developing a vaccine generally takes 5 to 10 years or longer, although the timeline can be compressed, as it was for COVID-19 vaccines.

Preclinical R&D

1–5

years

Vaccine candidates identified in lab and tested to determine their stability, toxicity and safety for use in humans

Phase 1 clinical trials

Testing in a small group (up to several dozen people) to determine a dose with an acceptable level of safety and preliminary estimate of biological and pharmacological effects

Phase 2 clinical trials

Testing in a larger group (up to several hundred people) to generate preliminary estimate of immunogenicity, safety, dose tolerability, and potential adverse effects

5–8

years

Phase 3 clinical trials

Testing in a larger group (tens of thousands of people) to provide a more definitive answer on the safety and efficacy of the intervention, often in randomized trials involving a known comparator product (a control)

Approval

0.5–2

years

Regulatory agency reviews

Manufacturing

Vaccine production facilities inspected

and scaled up

Distribution

Vaccines distributed to health care

providers and made available to the

public

Source:  CFR research.

There are some distinctions country-to-country. For example, the United Kingdom review process operates on analysis provided by the vaccine makers, while in the United States, regulators do their own analysis using raw data. In several countries, such as those in the European Union (EU), it’s common to have developers do their own rigorous testing in three rounds of trials growing in sample size, and then regulatory authorities do scientific evaluation. Many low- and middle-income countries heavily rely on WHO prequalifications to determine which medicines to use. 

The WHO can list a vaccine for recommended use. The agency gives this stamp when an inoculation is proven to have an efficacy rate of 50 percent or higher. It cannot approve a drug for use in any one country, but vaccine makers can request prequalification with the WHO to ensure it gets a significant endorsement for countries to follow. It can also help with disbursement; a principle goal of the WHO is to help countries achieve global coverage of at least 90 percent for essential vaccines by 2030.

Getting a vaccine from development to approval can be a rigorous and time-consuming process, with most estimates putting that timeline at about ten years. The COVID-19 vaccines, which saw fast-tracked production in an active public health emergency, were a notable exception. The record fastest time pre-COVID for the whole process was four years. There are efforts to reduce that time down to one hundred days for future health emergencies, says CFR Director for Global Health Thomas J. Bollyky.

What was ‘Operation Warp Speed’? 

When COVID-19 began tearing across the world in spring 2020, there were no vaccines to protect against the virus. 

To help accelerate the process, the U.S. government launched Operation Warp Speed in May 2020. It was a novel program to figure out how “instead of taking eight to twelve years to get a vaccine, you could do it in seven months,” then Secretary of Health and Human Services (HHS) Alex Azar said. The program was a public–private partnership that supported multiple vaccine developers based on preliminary evidence of success and good practices. It took interagency coordination between the Centers for Disease Control and Prevention (CDC), FDA, National Institutes of Health, HHS, and Departments of Agriculture and Defense, among others. 

The United States first began administering COVID vaccines in December 2020 to high-risk communities, and the first approved vaccine for wide public use came in August 2021. Since then, researchers say millions of infections, hospitalizations, and deaths have been avoided in vaccination campaigns. 

The operation achieved successful vaccines in record time in two ways. On the development side, it used mRNA, a molecule involved in protein synthesis, as a delivery mechanism allowing the vaccine to turbocharge through testing. The other was on the regulatory side: regulatory authorities were able to authorize it for emergency use. The WHO granted twelve of the vaccines emergency use listing to spur distribution as safely as possible to end lockdowns. 

How have other vaccines been effective?

Major health authorities including the WHO and CDC have promoted vaccination as the safest way to protect from illness, and much safer than getting sick. Vaccines have saved at least 150 million infant’s and children’s lives in the past fifty years alone in low- and middle-income countries, researchers at the University of Oxford’s data publisher Our World In Data estimate. The data tells the story of vaccine efficacy on several diseases: 

HPV. Human papillomavirus (HPV), a disease linked to cervical and other cancers, is one of the leading causes of cancer in women. The vaccine has been shown to cut cases by around 90 percent where it’s been implemented.  

Rotavirus. A diarrheal disease, rotavirus can be deadly among young children. The vaccine has led to up to 70 percent fewer hospitalizations for children under five years old in African countries.  

Polio. After the polio vaccine was rolled out in 1955, cases were nearly entirely stamped out. Combined with the WHO-led Global Polio Eradication Initiative that focused on eliminating the disease by 2000, basic immunization programs have been supported worldwide to bring levels down to near eradication.

Measles. Before the vaccine became available in 1963, most children contracted the disease by fifteen years old, leading to around fifty thousand hospitalizations each year. Due to vaccination efforts, the United States was able to declare measles eradicated in 2000. However, in recent months, outbreaks have begun to crop up again, with the first major case detected in Texas in February 2025. Since then, health officials have recorded at least six hundred cases, the highest count since 2019. In April 2025, the United States recorded its second death of an unvaccinated child as the cases have spread to more than twenty states. 

What are the challenges in vaccination efforts?

Factors complicating vaccination include:

Availability of supply. If a government is unprepared for a disease outbreak, it can take a long time, often at least ten years, to either create a vaccine or produce and administer the amount needed for the population.

Equity of procurement is another supply concern. Historically, less-developed countries in the so-called Global South have been the lowest on the list to get vaccines since major vaccine development centers tend to be clustered in wealthier, more developed countries. The resulting effect breeds resentment, political tensions, and distrust—a phenomenon that WHO Director-General Tedros Adhanom Ghebreyesus has called “vaccine apartheid,” referring to the COVID-19 pandemic. 

Administration. Lack of access to care is one of the top constraints. The sheer logistics of getting to clinics, such as those in remote, rural areas, and setting up appointments, are a huge barrier, says CFR Senior Fellow for Global Health Prashant Yadav. If vaccine supply happens to run out the day someone visits a clinic, which is not uncommon, he says, some studies show that “50 percent [of people] don’t come back.” 

Areas facing violence often are unable to provide medical services, and new disease outbreaks can occur as humanitarian conditions worsen. For example, Gaza has experienced a resurgence in polio, and Sudan has seen cholera outbreaks and HIV prevalence tick up. 

Demand. A rise in the number of people—in recent opinion surveys of U.S. adults, nearly double that of 2021—who either are against vaccines or are wary of them has caused issues in protecting populations against disease.

Why is vaccine skepticism on the rise?

A wave of global hesitancy about vaccines has bubbled up in recent years, owing to a few root causes.

Vaccine withdrawals have raised concerns among the public. Two studies that linked vaccinations with developing autism published more than twenty years ago have been popular arguments among antivaxxers as well. However, many studies have since debunked this correlation, concluding that the two studies were critically flawed. A swine flu vaccine in 1976 similarly faced severe backlash when it was linked to an increased risk of a serious neurological disorder called Guillain-Barré Syndrome. The U.S. vaccination program was abruptly terminated. “The events dented confidence in public health for years to come,” the BBC wrote in 2020 on the incident. 

The rising tide of trepidation stems from many factors, but many experts say it is largely driven by mounting misinformation. It is true that there is a small percentage of the population that has adverse reactions to vaccines, but such instances have become exaggerated. The inaccurate information often comes from social media posts sensationalizing or spreading conspiracy theories and disinformation online, but it can even come from political leaders and foreign actors, such as Russia seeking to sow distrust in the U.S. government. (Several of President Donald Trump’s leading health officials, including RFK, have been vocal critics of vaccines.) CFR’s Yadav says a lack of effective public health messaging has allowed misinformation to thrive.

But the hesitation to get vaccinated has consequences beyond individual health: it harms the greater population, experts say. The WHO has labeled vaccine hesitancy as one of the top ten threats to global health. Vaccination rates have dipped below herd immunity for some highly communicable diseases, even in places like the United States, where the disease has been less challenging to eradicate. 

Outbreaks of vaccine-preventable diseases have been rising worldwide since 2020. Concerns about the rapid production of the COVID vaccines and politicization of the U.S. government’s response measures led to significant hesitation from some who opt not to get the vaccine. That has since spilled over into other diseases in years following, health experts believe, as diseases previously almost nonexistent such as measles are on the rise again.

How can countries contribute to global vaccination goals?

Wealthy countries can channel more into supporting other countries when diseases arise, aid experts have said. In one recent example, the United States, Canada, the EU, and others stepped in early to funnel vaccines to several countries to help counter the mpox surge in 2024. Sending vaccines to countries in need is only the first step, experts say. Allocating funds to distribute them is the next one, thus ensuring that once delivered, they actually wind up in pharmacies and on clinic shelves. Yadav sees drones as one promising solution; pilot programs in countries including Ghana and Rwanda have been shown to work.

Other important solutions to these issues include wealthy countries helping lower-income regions produce their own vaccines and build out their health infrastructure. The African Vaccine Manufacturing Accelerator, for example, is a five-year initiative supported by Gavi, a global vaccine alliance organization, to ensure African countries can make more vaccines locally. The African Union has set a goal to manufacture 60 percent of vaccines locally by 2040. 

Messaging is another crucial fight, experts, including Yadav, say. “Some combination of health expert advice and social network-relevant advice is what changes the lack of information, and to some degree, the misinformation piece,” he says. Brazil is another example of a country that has made concerted efforts to debunk vaccine rumors, launching a vaccine education movement that has improved vaccination rates. 

Is the United States shifting away from being a vaccine leader?

The United States has historically been the biggest donor toward global health initiatives, including vaccination programs. In 2024, the U.S. budget for global health was $12 billion, which is only 0.1 percent of the entire U.S. government budget. 

This progress could be at risk, health experts say. On his first day in office, President Trump withdrew the United States from the WHO, which would wind up with the WHO losing nearly a fifth of its funding and has shut down at least 83 percent of programs—many of which provided vital health support—housed under the U.S. Agency for International Development. “Without a strong partnership with WHO, some of this effort in advanced science doesn’t translate as quickly,” Yadav says. The WHO could no longer be as prone to endorse U.S.-made vaccines, and other countries could be less likely to trust them. Trump also put an end to any U.S. funding for Gavi, which vaccinates roughly 70 million children every year. 

Pulling the plug on funding health efforts abroad hurts the United States as well. “Better infectious disease management systems abroad make it less likely that terrifying infectious diseases, like Ebola, will become a problem at home,” CFR Africa expert Michelle Gavin writes. 

Internally, Trump has put forward some known anti-vaccine advocates to lead his cabinet, including RFK Jr. So far, the Trump administration has largely turned away from vaccine support, coming under scrutiny for downplaying the measles outbreak and inflating the vaccine’s harms, staying markedly quiet on the growing avian flu cases, and defunding programs geared toward making vaccines more effective and widespread. Trump’s 2025 raft of tariffs lodged against other countries—which includes pharmaceutical levies—is also likely to constrain the supply chain of medicine in the United States, several experts have noted.

Further, RFK has announced that he will reevaluate the childhood vaccination schedule, despite previously pledging not to change it. In March 2025, he hired a discredited vaccine skeptic to oversee a review of any tie between vaccinations and autism, a long-debunked claim. Days earlier, the longtime top vaccine official in the FDA resigned over what he called Kennedy’s “misinformation and lies.”  

Will Merrow and Hyojin Yoo created the graphics for this article.