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.

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 CDC shingles researcher.

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.”

What’s causing the enthusiasm: Shingrix, which pharmaceutical firm GlaxoSmithKline intends to begin shipping this month. Large international trials have shown that the vaccine prevents more than 90 percent of shingles cases, even at older ages.

The currently available shingles vaccine, called Zostavax, only prevents about half of shingles cases in those older than 60 and has demonstrated far less effectiveness among elderly patients.

Yet those are the people most at risk for this blistering disease, with its often intense pain, its threat to vision and the associated nerve pain that sometimes last months, even years.

Nearly all older Americans harbor the varicella zoster virus that causes shingles; it came it with childhood chickenpox, whether they knew they had the disease or not.

The virus stays dormant until it erupts decades later. The risk rises sharply after 50.

Shingles is hardly a minor menace. “A million cases occur in the United States each and every year,” Schaffner said. “If you’re fortunate enough to reach your 80th birthday, you stand a 1-in-3 to 1-in-2 chance of shingles.”

Preventing the great majority of these cases — along with the risk of lingering and debilitating nerve pain, called postherpetic neuralgia — would represent a major advance in public health.

So while the old vaccine will remain on the market, the CDC committee voted to make Shingrix the preferred vaccine and recommended it for all adults older than 50 — a group younger by a decade than those earlier encouraged to get Zostavax.

The committee also recommended Shingrix for adults who have previously gotten Zostavax, since a smaller study in people older than 65 demonstrated effectiveness and safety in those already vaccinated. The Food and Drug Administration approved Shingrix last month.

Once the CDC’s director endorses the panel’s recommendations, and the agency publishes them, insurers — including Medicare and Medicaid — will start coverage.

“By early 2018, it should be broadly available to consumers in the U.S.,” said Dr. Thomas Breuer, chief medical officer of GSK Vaccines. Canada has also approved Shingrix; it awaits approval in Australia, Japan and Europe.