Zostavax was the original shingles vaccine. It came out six years before Shingrix.
Based on my incomplete knowledge, Zostavax was pulled because it provided only 50% protection, and its duration was unknown, possibly less than 5 years.
Shingrix, on the other hand, provides about 90% protection, and is believed to have long term duration.
Though eight members voted in favor of preferring Shingrix, Pellegrini and six others voted against the motion.
https://www.cnn.com/2017/10/25/health/cdc-new-shingles-vaccine/index.html
https://www.sokolovelaw.com/blog/zostavax-shingles-vaccine-lawsuits/
“Lawsuits against Merck have taken issue with the company’s warnings, claiming Merck did not properly inform them of all the side effects beyond a few minor ones such as inflammation at the base of injection or a fever.
Memos from the U.S. Department of Health and Human Services (DHHS) show that some of these warnings were only added on much later. For example, a warning about eye inflammation was added in early 2016—nearly a decade after Zostavax was first approved by the FDA.”