Are vaccines an effective tool to prevent disease?

Vaccines are proven to prevent disease — I'll pull the latest evidence on how well they work.

Yes — vaccines are one of the most effective tools to prevent infectious disease. The scientific consensus from the World Health Organization (WHO), CDC and other public health agencies is that vaccination prevents infection, severe illness, hospitalization, disability and death, and also protects communities.

1. Vaccination is ranked among the most effective prevention methods

> Vaccination is one of the most effective ways to prevent diseases.

> Vaccines are the most effective tool to prevent illness, hospitalizations, and deaths.

WHO notes that vaccines are very safe and rigorously tested, but that like any medicine they can have minor, short-term side effects — a person is far more likely to be seriously harmed by the disease than by the vaccine.

2. Large-scale historical impact

Over the past 50 years:
> essential vaccines against just 14 diseases have saved at least 154 million lives

Other WHO estimates phrase this as:
> vaccines have saved more than 150 million lives, as ordinary people chose to protect themselves, their children and their communities from diseases like measles, diphtheria, pertussis, polio, and rotavirus.

That is:
> more than 3 million lives a year or six people every minute for five decades

> Vaccines are among the most cost-effective ways to protect against infectious diseases. The introduction of a vaccine has, in many cases, led to a very large decrease in the incidence of the targeted disease — such as the 96% decrease in the incidence of polio that occurred within 7 years of the introduction of the Salk and Sabin polio vaccines

Vaccines are considered one of the greatest medical achievements and:
> They have eradicated smallpox and reduced global child mortality and long-term disabilities from vaccine-preventable diseases.

In the United States:
> Childhood vaccination in the U.S. has been very successful in preventing illness and death. Serious diseases such as diphtheria, mumps, and rubella, once common at young ages, are now practically unheard of.

3. Measured effectiveness by disease

Effectiveness varies by vaccine, disease, age and how well the vaccine matches circulating strains, but randomized trials and real-world studies show high protection — especially against severe outcomes:

> overall varicella vaccine effectiveness is 82% after 1 dose and 92 to 98% after 2 doses; effectiveness against severe varicella is 100% after even 1 dose

> Flu vaccination reduced the risk of severe flu in children by 78% against similar flu A ... The study also found that the vaccine was 76% effective at preventing lifethreatening influenza

> safe and highly effective at preventing infectious diseases like COVID-19
and have shown
> over 90% effectiveness in preventing hospitalization from the original strains
WHO research as of December 2025 concluded:
> Up-to-date vaccination remains the most effective way to prevent severe COVID-19 illness

It is noted that:
> Vaccines cannot always prevent infection, but they can substantially reduce the risk of serious disease.

4. How vaccines prevent disease - individual and community protection

Vaccines work by introducing a harmless piece of a pathogen or weakened pathogen to trigger antibodies and immune memory, so the body can fend off real infection for years or a lifetime without causing the disease.

Vaccines also create herd immunity:

> Herd immunity describes how a population is protected from a disease after vaccination by stopping the germ responsible for the infection being transmitted between people.

> By being vaccinated an individual is not only protected from being infected themselves but they then also cannot pass this infection onto other people, where it may cause severe disease.

This indirect protection is critical for people who cannot be vaccinated, such as newborns or immunocompromised individuals. For highly contagious diseases like measles, 90-95% coverage is needed for herd immunity to work.

For this reason researchers describe:
> vaccines are the most effective and cost-efficient healthcare intervention we have.

Limitations

No vaccine is 100% effective for 100% of recipients, and protection can wane or be reduced by new viral variants. Effectiveness must be measured against specific outcomes (infection vs. hospitalization vs. death) and some vaccines require boosters. Continuous monitoring by national regulators and WHO's Global Advisory Committee on Vaccine Safety ensures safety and efficacy after introduction.

In summary, decades of clinical trials, surveillance and global immunization programs show vaccines are a highly effective, safe and cost-efficient tool for preventing disease at both the individual and population level. If you have questions about which vaccines are recommended for you or your children, talk to a healthcare provider or local public health authority.