Medical researchers and government health policymakers, a cautious lot, normally take pains to keep expectations modest when they’re discussing some new finding or treatment.

They warn about studies’ limitations. They point out what isn’t known. They emphasize that correlation doesn’t mean causation.

So it’s startling to hear prominent experts sound positively excited about a new shingles vaccine that an advisory committee to the Centers for Disease Control and Prevention approved last month.

“This really is a sea change,” said Dr. Rafael Harpaz, a veteran shingles researcher at the C.D.C.

Dr. William Schaffner, preventive disease specialist at the Vanderbilt University School of Medicine, said, “This vaccine has spectacular initial protection rates in every age group. The immune system of a 70- or 80-year-old responds as if the person were only 25 or 30.”