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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Thimerosal-Mercury

Mercury in Vaccines

This article answers the most frequently asked questions about thimerosal and its use as a preservative in vaccines.

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