The simple truth is that the flu shot cannot cause the flu. The injectable flu vaccine is a killed-virus vaccine and is thus unable to give a recipient the flu.

In general, vaccines are monitored for their immediate safety. So if a significant vaccine side effect occurs within days or a few weeks of administering the vaccine, then it will likely be noticed by the Vaccine Adverse Event Reporting System (VAERS).

A “hot lot” is the name given by antivaccine groups to describe a given manufacturing lot of vaccine as particularly reactive, meaning it has had a larger number of side effects than other lots of the same medicine. It is believed by some that there have been hot lots recalled and destroyed because of such serious side effects.

While this statement is sometimes used in antivaccine literature to show that vaccines don’t work, in truth it shows the benefits of vaccines.

Aluminum is an ingredient that is present in vaccines in relatively high concentrations.  Aluminum is used as an adjuvant in several vaccines, which means that it is present in the vaccines to make the vaccine more effective. The aluminum also seems to make the vaccines more reactive, meaning it causes more side effects. For example, one HPV vaccine study compared a saline placebo with an aluminum-containing placebo with the Gardasil vaccine. (A placebo is an inert material that is designed as a control to study the effectiveness of the vaccine.)