Are vaccines an effective tool to prevent disease?

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

Yes, vaccines are one of the most effective tools to prevent disease — this is the consensus of major health authorities including the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC).

How effective are they?

Vaccination is considered one of the most effective medical interventions ever developed:

> Vaccination is one of the most effective ways to prevent diseases. Over the past 50 years, essential vaccines against just 14 diseases have saved at least 154 million lives

> Vaccination is one of the most effective interventions against infectious diseases and is estimated to prevent 2-3 million deaths annually, with an additional 1.5 million deaths that could be averted with improvements in global vaccination coverage

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

WHO describes vaccines as:

> "Vaccines are among the most powerful inventions in history, making once-feared diseases preventable"

Evidence of impact

1. Global lives saved:
A landmark WHO-led study published in The Lancet found global immunization efforts saved an estimated 154 million lives over 50 years (1974-2024), or 6 lives every minute, with 101 million being infants. Of those, measles vaccination had the most significant impact, accounting for 60% of the lives saved.

The study also found vaccination against 14 diseases (diphtheria, Haemophilus influenzae type B, hepatitis B, Japanese encephalitis, measles, meningitis A, pertussis, invasive pneumococcal disease, polio, rotavirus, rubella, tetanus, tuberculosis, and yellow fever) directly contributed to reducing infant deaths by 40% globally, and by more than 50% in the African Region.

2. Eradication and near-eradication:
> Thanks to vaccines, smallpox has been eradicated, polio is on the brink, and with the more recent development of vaccines against diseases like malaria and cervical cancer, we are pushing back the frontiers of disease

Smallpox remains the only human disease eradicated worldwide, and polio has been targeted for eradication through vaccination.

Historically:

> In 2013, it was estimated that 103 million cases of childhood diseases in the United States had been prevented by the use of vaccines since 1924

> for children born in the United States during the period 1994–2013 vaccines will have prevented 322 million illnesses, 21 million hospitalizations, and 732,000 premature deaths

The introduction of a vaccine has, in many cases, led to a very large decrease in incidence — 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

3. Vaccine efficacy and effectiveness in trials and real world:

WHO explains:

> Vaccines are safe, effective and life-saving. Before approval by relevant regulatory agencies, vaccines undergo rigorous clinical trials to test their quality, safety and efficacy

Examples of effectiveness:

4. Community protection (herd immunity):

Vaccines protect both individuals and communities:

> Vaccines not only protect those who have been immunized, but can also reduce disease among those who cannot be immunized

When coverage is high enough (e.g., 95% with 2 doses of measles-containing vaccine is needed to protect communities from outbreaks), transmission is interrupted, protecting vulnerable people who cannot be vaccinated.

Limitations - not 100% protection

Vaccines do not provide 100% protection because of individual differences in immunity and response to infection

> Breakthrough infections’ – where people get infected despite having been fully vaccinated – can occur

> 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 can also wane over time (requiring booster doses) and variants can slightly impact ability to guard against mild disease and infection, though vaccines remain effective against severe disease, hospitalization and death.

Conclusion

The evidence from 50+ years of global data shows vaccines are a highly effective, safe, and cost-effective tool for preventing disease, disability and death — from common childhood illnesses to pandemic viruses. They work best when coverage is high, schedules are followed, and they are used together with other public health measures.