Are vaccines an effective tool to prevent disease?

Vaccines are proven to prevent disease — I'll gather the latest evidence on their effectiveness and safety.

Yes, vaccines are one of the most effective tools to prevent disease.

> 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

Major health authorities describe vaccines as among the most powerful inventions in history and one of the most successful and cost-effective public health tools available.

1. How vaccines prevent disease

> Immunization is a global health success story, saving millions of lives every year. Vaccines reduce risks of getting a disease by working with your body's natural defenses to build protection. When you get a vaccine, your immune system responds.

More specifically:

> Vaccines work by imitating an infection to engage the body's natural defenses.

> Vaccines help the body learn how to defend itself from disease without the dangers of a full-blown infection.

We now have vaccines to prevent more than 30 life-threatening diseases and infections.

2. Historical and current evidence of effectiveness

History has shown:

> Vaccines are highly effective: History has shown us that vaccines are one of the most effective tools in preventing and controlling outbreaks. Vaccines have successfully eradicated diseases like smallpox and significantly reduced the incidence of others such as polio and measles.

> Thanks to vaccines, smallpox has been eradicated, polio is on the brink, and many once-feared diseases can now be easily prevented, including measles, cervical cancer, yellow fever, pneumonia and diarrhoea.

3. Current global impact

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

Other estimates:

> Vaccines prevent up to 3 million deaths worldwide every year.

In the United States alone:

> 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.

> Over the past 50 years, 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.

4. How effective are they?

Effectiveness varies by vaccine and disease:

> According to the CDC, "vaccines are generally 90% to 99% effective in preventing disease."

> For some vaccines, like smallpox, measles, or polio, this means they completely prevent disease in most people. For others, like flu or COVID, this means they substantially reduce disease severity and prevent hospitalization and death.

Recent reviews confirm:

> mRNA vaccines—now administered billions of times worldwide—are safe and highly effective at preventing infectious diseases like COVID-19

Vaccines are also critical to the prevention and control of infectious disease outbreaks. They underpin global health security and are a vital tool in the battle against antimicrobial resistance.

5. Are vaccines perfect?

No vaccine is 100% effective for every person, and protection can wane over time requiring boosters. Effectiveness can also be lower against mild infection while remaining high against severe disease, hospitalization and death. For example, flu vaccines substantially reduce severity if a person does get sick.

However, even imperfect vaccines reduce spread through community or herd immunity — when enough people are vaccinated, transmission slows and protects those who cannot be vaccinated.

Vaccines undergo rigorous testing — Phase I in small groups of 20-50 people, Phase II in several hundred, Phase III in thousands — and continued safety monitoring at local, national and global levels after introduction.

Conclusion: The overwhelming weight of scientific evidence and over 50 years of global experience shows vaccination is an extremely effective, safe, and cost-effective tool to prevent infectious diseases, save millions of lives annually, and in the case of smallpox, eradicate a disease entirely.