Are vaccines an effective tool to prevent disease?

I'll gather the latest evidence on how well vaccines prevent disease.

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

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.

> Vaccines train your immune system to create antibodies, just as it does when it’s exposed to a disease. However, because vaccines contain only killed or weakened forms of germs like viruses or bacteria, they do not cause the disease or put you at risk of its complications.

> 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.

We now have vaccines to prevent more than 30 life-threatening diseases and infections including cervical cancer, cholera, COVID-19, diphtheria, hepatitis B, influenza, measles, polio and others, helping people of all ages live longer, healthier lives.

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

Evidence of Effectiveness

Global health authorities describe:

> 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

> 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:

> 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

> Vaccines can provide cost-effective, long-term protection and have resulted in the eradication of two major pathogens, rinderpest and smallpox, as well as the local elimination of others, such as measles

Specific impacts:

Vaccines are likely staying effective against variants because of the broad immune response they cause, which means that virus changes or mutations are unlikely to make vaccines ineffective

Herd Immunity and Eradication

Vaccines protect individuals and communities:

> Herd immunity makes it possible to protect the population from a disease, including those who can't be vaccinated, such as newborns or those who have compromised immune systems.

> Using the concept of herd immunity, vaccines have successfully controlled deadly contagious diseases such as smallpox, polio, diphtheria, rubella and many others.

To date, two diseases have been eradicated using herd immunity and vaccination: rinderpest and smallpox.

Limitations

Vaccines are highly effective but not 100% perfect:

> Vaccines do not provide full (100%) protection because of many factors, including our individual differences in immunity and response to infection.

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

However, 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.

In summary, evidence from the World Health Organization, CDC and peer-reviewed studies shows vaccination is considered the most successful and cost-effective medical intervention ever for preventing infectious disease, reducing mortality, hospitalization and long-term disability, and enabling eradication and elimination of major diseases.