Vaccinations and Infectious Disease: Separating Fear From Fact

Most vaccines use inactivated (killed) viruses, weakened (attenuated) forms, individual proteins from a pathogen's surface, or — as with mRNA vaccines — genetic instructions that prompt your cells to produce a recognizable protein. None of these mechanisms can produce a full infection. Some people experience mild symptoms such as a sore arm or low-grade fever after vaccination; this reflects the immune system responding and building defenses, not an infection.

Infants encounter thousands of antigens (substances that trigger an immune response) from the environment every day. The antigens introduced by the entire childhood vaccine schedule represent a tiny fraction of what the immune system routinely manages. The schedule recommended by the ACIP and the American Academy of Pediatrics is continuously reviewed for both safety and effectiveness. Spacing vaccines out — or delaying them — leaves children unprotected during the period when diseases like whooping cough (pertussis) are most dangerous.

For some diseases, natural infection does generate a robust immune response. However, that immunity arrives only after surviving the illness, which carries risks of serious complications, hospitalization, and death. Vaccines are specifically engineered to stimulate durable immunity while avoiding those risks. For diseases like hepatitis B or HPV, vaccines can provide protection that is comparable to — or in some respects more consistent than — natural infection, without the associated harms.

Thimerosal, a mercury-based preservative once used in some multi-dose vaccines, has been removed from or reduced to trace levels in virtually all childhood vaccines as a precautionary measure — even though research had not established it as harmful at those doses. Aluminum salts (adjuvants) appear in some vaccines to help stimulate a stronger immune response; the amounts are far below what humans ingest daily through food and water. Regulatory agencies including the FDA evaluate every vaccine ingredient for safety before approval.

Smallpox is the only human infectious disease eradicated globally through vaccination. Every other vaccine-preventable disease still circulates in parts of the world, meaning unvaccinated populations remain at risk through travel and imported cases. Polio, once feared across the United States, has been eliminated domestically — but cases persist elsewhere, making continued vaccination essential. Reducing vaccine coverage before eradication is confirmed historically leads to outbreaks.

This myth originated primarily from a 1998 study that was later retracted due to serious ethical violations and data manipulation. Since then, research involving populations across the United States, Denmark, Japan, and elsewhere has consistently found no connection between the MMR vaccine — or any other vaccine — and autism. Autism symptoms are often first recognized around the same age children receive routine vaccinations, which can create a misleading sense of association where no causal link exists.