Are vaccines an effective tool to prevent disease?

I'll pull together evidence on vaccines' effectiveness in preventing disease.

Yes, vaccines are considered one of the most effective tools to prevent infectious disease by major public health authorities and scientific evidence.

Effectiveness at Population Level

> 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

The World Health Organization (WHO) describes vaccines as:

> Vaccines are safe, effective and life-saving

The U.S. Centers for Disease Control and Prevention (CDC) states:

> History shows that vaccines are the safest, most effective way to protect yourself and your family from many preventable diseases

Historical Impact - Disease Eradication and Reduction

Vaccines have led to dramatic declines in incidence and mortality for many diseases:

Specific examples in the United States during the 'vaccines for children era' (1994-2013):

> the total number prevented by routine childhood vaccinations in the USA was more than 322 million cases of infectious diseases, 21 million hospitalisations, and 731,700 deaths

Other measured impacts include:

> Based on the 2021-2022 flu disease burden estimates along with vaccine coverage and vaccine effectiveness data, CDC estimates that 1.9 million flu-related illnesses, 990,000 flu-related medical visits, 26,000 flu-related hospitalizations, and 1,500 flu-related deaths were prevented by flu vaccination

How Vaccines Work to Prevent Disease

> 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
> Vaccines work by imitating an infection—the presence of a disease-causing organism in the body—to engage the body's natural defenses

The active ingredient in all vaccines is an antigen:

> either Weakened or killed bacteria or viruses Bits of their exterior surface or genetic material, or Bacterial toxin treated to make it non-toxic

This stimulates the immune system to produce antibodies:

> Antibodies are proteins produced by white blood cells to identify and neutralize foreign substances

After vaccination, if the person is later exposed to the pathogen, the immune system can respond immediately. This creates vaccine-induced immunity, which takes longer to develop but lasts longer than passive immunity.

Vaccine Efficacy vs. Effectiveness

Real-world examples:

> the vaccine effectiveness of BNT162b2 or mRNA-1273 COVID-19 vaccines in preventing SARS-CoV-2 infection was 90% for full immunization and 80% for partial immunization in the US

Limitations

Vaccines do not provide 100% protection:

> Vaccines can stop most people from getting sick, but not everyone
> 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
> vaccinated people can and sometimes do get infected. But a vaccinated person is far less likely to die or become seriously ill than someone whose immune system is unprepared to fight an infection

Protection can also wane over time and variants can affect effectiveness, which is why primary series and booster doses are recommended, and why for diseases like influenza the vaccine is reformulated each year.

Vaccines undergo rigorous testing and continuous safety monitoring, and serious side effects are extremely rare compared to the risk of severe illness, disability and death from the diseases they prevent.

In summary, extensive historical, epidemiological, and clinical trial evidence supports that vaccines are a highly effective, cost-effective, and life-saving tool to prevent infectious diseases at both individual and population levels, though they work best when administered on schedule and with high coverage to also provide community protection.