Vaccines are classified as “biologics” rather than drugs, allowing LESS rigorous safety testing than is required for new drugs. For example, most drug trials follow 1000+ patients over months or years and use a saline or sugar placebo. In contrast, vaccines are routinely tested for just days or weeks and DO NOT use a placebo as the control.
In fact, no vaccine has EVER been tested against a true placebo. Instead, manufacturers use other vaccines or other vaccine ingredients (aluminum and preservatives, etc.) as the placebo. This means that if these ingredients in a vaccine are causing adverse side effects, BOTH the test group and the control group will experience the same side effects. As a result, a new vaccine can be declared safe and added to the schedule because it appears to have no additional side effects.
It's also important to know that vaccines are approved individually, meaning that safety testing is not routinely conducted on the effects of giving children multiple vaccines in a single doctor’s visit as called for in the CDC schedule. In addition, all vaccine inserts state that the vaccine "has not been evaluated for carcinogenic or mutagenic potential or potential to impair fertility."
The clinical trials for Merck’s Hepatitis B vaccine monitored fewer than 150 infants and children for only five days AND used other vaccine ingredients as the placebo. Despite this less-than-rigorous testing, the HepB vaccine is given to all babies on day of birth.