The Varivax varicella vaccine by Merck was launched in 1995.

 

In a testimony by "Karen Midthun, M.D., Director, Office of Vaccines Research

and Review (OVRR), Center for Biologics Evaluation and Research (CBER) at the Food and Drug Administration", she mentions a study Merck was supposed to complete 15 years after licensure 

"the manufacturer of Varicella Virus Vaccine committed to perform a post-licensure study

with fifteen years of safety follow-up. These studies will provide information about the effects of the vaccine in a

population larger than that exposed during clinical trials. If additional side effects are identified during the postmarketing

phase, either pursuant to adverse event reports filed by health care providers or consumers, or

pursuant to Phase IV studies, FDA would take appropriate regulatory action to protect the public health such as,

among other options, changing the product's labeling information to reflect the possible side effects, or, in cases

of imminent or substantial hazard to the public health, ordering a recall of the product."

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Merck did complete a study, but it did not include the effects of the vaccine or any adverse reactions. Due to this major flaw within the study, the sole purpose of the study, the FDA cannot take required measures for the vaccine ex. changing of labeling or product recall.