Are vaccines an effective tool to prevent disease?

Vaccines are a proven disease prevention tool — I'll pull the latest effectiveness evidence to answer you.

Yes, vaccines are one of the most effective tools to prevent disease - this is supported by decades of scientific research and global public health data.

Scientific consensus

•Decades of scientific research confirming that vaccines are one of the most effective tools for preventing serious diseases.

•Vaccines are the safest and most effective way to prevent the spread of infectious diseases, including measles, whooping cough and polio.

•Scientific research confirms that vaccines are safe and effective—and they protect children and teens from serious diseases.

•The clinical efficacy and effectiveness of vaccines are beyond question, with a wealth of scientific evidence demonstrating their ability to reduce disease incidence and prevalence, prevent severe health complications, and save lives.

Before approval, vaccines undergo rigorous clinical trials to test their quality, safety and efficacy. After approval, they continue to be closely monitored for ongoing safety and effectiveness. Vaccines are safe, effective and life-saving.

How they work

Vaccines reduce risks of getting a disease by working with your body’s natural defenses to build protection.

•They protect our bodies against specific diseases by triggering the immune system to produce antibodies to "fight them off".

•Vaccines train our immune systems to create proteins that fight disease, known as ‘antibodies’, just as would happen when we are exposed to a disease but — crucially — vaccines work without making us sick.

•Vaccinated people are protected from getting the disease in question and passing it on, breaking any chains of transmission.

When enough people are vaccinated, it creates herd immunity:

•Widespread vaccinations may produce a phenomenon known as herd immunity or community immunity. This occurs when diseases can’t affect a community because so many people have been immunized

•Herd immunity is a form of indirect protection that provides a measure of protection for individuals who are not immune.

Vaccines are also critical to the prevention and control of infectious disease outbreaks.

How well they work in practice

> We now have vaccines to prevent more than 30 life-threatening diseases and infections, helping people of all ages live longer, healthier lives.

> There are currently vaccines available for more than 20 life-threatening diseases; these vaccines help to prevent and control infectious disease outbreaks.

The World Health Organization asserts immunizations are the most cost-effective health interventions.

Vaccinations are one of the most impactful public health interventions, saving millions of lives annually and reducing the spread of infectious diseases.

•Immunization currently prevents 3.5 million to 5 million deaths every year from diseases like diphtheria, tetanus, pertussis (whooping cough), influenza and measles.

•Vaccines prevent an estimated more than 4 million deaths worldwide every year. In the United States alone, routine childhood immunizations among children born between 1994 and 2023 are estimated to have prevented over one million deaths.

•Research shows that routine vaccinations for children born during 1994–2023 will have prevented about 508 million illnesses and 32 million hospitalizations and saved over 1.1 million lives.

•Most childhood vaccines are over 90% effective at protecting against disease.

Specific examples:

•The measles vaccine is about 97% effective after two doses, drastically reducing the incidence of measles outbreaks.

•Two doses of the MMR vaccine are about 97% effective at preventing measles, with one dose about 93% effective.

•The widespread use of the measles vaccine has led to a 73% decrease in measles deaths between 2000 and 2018 due to vaccination efforts.

•Smallpox, a deadly disease that killed millions, was eradicated globally in 1980 following a successful vaccination campaign.

•Polio, once a feared disease causing paralysis and death, has been nearly eradicated worldwide thanks to the polio vaccine.

Efficacy vs. effectiveness and limitations

To understand how well vaccines work, it is important to distinguish vaccine efficacy and effectiveness:

•Vaccine efficacy is measured in controlled clinical trials. It is based on how many people who got vaccinated developed the ‘outcome of interest’ compared with how many people who got the placebo developed the same outcome.

•Vaccine effectiveness refers to how well vaccines work in the real world.

Vaccines do not provide 100% protection:

•Vaccines can stop most people from getting sick, but not everyone. Even after someone receives all of the recommended doses and waits a few weeks for immunity to build up, there is still a chance that they can get infected. Vaccines do not provide full (100%) protection because of many factors, including our individual differences in immunity and response to infection.

•If vaccinated people do get sick, they are likely to have milder symptoms, in general 'It is very rare for someone vaccinated to experience severe illness or die.

Protection may weaken over time and some vaccines require booster doses to strengthen and extend protection, and new variants can affect protection, which WHO continuously monitors.

In summary, vaccines do not guarantee absolute prevention for every individual, but at both individual and population levels they are highly effective at preventing infection, severe disease, complications, hospitalization and death, and are a cornerstone of preventing outbreaks and achieving community immunity.

Citations (4)

1who.intGovernment
Vaccine efficacy, effectiveness and protection
Backs: “The clinical efficacy and effectiveness of vaccines are beyond question, with a wealth of scientific evidence demonstrating their ability to reduce disease incidence and prevalence, prevent severe health complications, and save lives. Before approval, vaccines undergo rigorous clinical trials to test their quality,…”
2who.intGovernment
Know the facts
Backs: “After approval, they continue to be closely monitored for ongoing safety and effectiveness. Vaccines are safe, effective and life-saving. How they work”
3pmc.ncbi.nlm.nih.govAcademic
Value of Vaccinations: A Fundamental Public Health Priority to Be Fully Evaluated - PMC
Backs: “There are currently vaccines available for more than 20 life-threatening diseases; these vaccines help to prevent and control infectious disease outbreaks. The World Health Organization asserts immunizations are the most cost-effective health interventions. Vaccinations are one of the most impactful public health…”
4cdc.govGovernment
Vaccines and the Diseases they Prevent
Backs: “In the United States alone, routine childhood immunizations among children born between 1994 and 2023 are estimated to have prevented over one million deaths. Research shows that routine vaccinations for children born during 1994–2023 will have prevented about 508 million illnesses and 32 million hospitalizations and…”