The National Network for Immunization Information (NNii) provides up-to-date, science-based information to healthcare professionals, the media, and the public: everyone who needs to know the facts about vaccines and immunization.

Vaccine Safety

Cause or Coincidence

When an adverse event occurs after vaccination, it needs to be determined whether the adverse event was caused by the vaccine or whether it was just coincidental in time with the administration of the vaccine—that is, it was going to happen anyway. How can researchers determine if a vaccine causes a particular disease or not?

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Vaccine Components

Aluminum Adjuvants in Vaccines

Some vaccines contain chemicals called adjuvants to help stimulate the production of immunity against the vaccine ingredients, making the vaccine more effective. In the United States, aluminum salts have frequently been incorporated as adjuvants in vaccines.

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