The CDC recommends that people 50 and older get the Shingrix vaccine even if they have had shingles, aren’t sure whether they ever had chickenpox, or previously received the older shingles vaccine, Zostavax. (iStock)

Ann Dieffenbach got her first shot of the new shingles vaccine, Shingrix, at her CVS pharmacy in Bethesda on Feb. 25. It’s a two-injection series, the second shot recommended two to six months after the first. But Dieffenbach, 63, hasn’t yet been able to get that second shot: There has been no vaccine available.

She has called numerous stores, only to be told it’s on back order. In a few weeks, her six months will be up. “It’s been frustrating,” says Dieffenbach, a retired National Institutes of Health communications director. “I haven’t even been able to find a place that will put me on a waiting list.”

Dieffenbach is not alone. Many people nationwide are between shots, unable to complete the series. Until recently, I was one of them. I got my first shot at a CVS in Northwest Washington at the end of April, then went back recently for the second — only to be placed on a waiting list.

There is good news, though. The vaccine maker, GlaxoSmithKline, recently started shipments again, and the shortage has begun to ease.

The manufacturer blames the problem on extraordinarily high demand. “It is not a manufacturing issue,” says Sean Clements, a company spokesman. “The demand for this vaccine has been unprecedented.”

Still, the shortage raises questions for those who may be nervously watching the calendar: What happens if your six months elapse? Must you begin the shots all over again?

The answer: No, you don’t have to restart the series. But if you can help it, don’t dawdle.

The Centers for Disease Control and Prevention, which issues vaccine recommendations, says patients who wait longer than six months needn’t worry, but they should get that second dose as soon as possible. Be sure not to skip it, because two doses convey the maximum immunity, more than 90 percent.

Shingles afflicts 1 in 3 people at some point, causing an estimated 1 million cases annually in the United States. The risk increases with age. The disease, caused by a reactivation of the virus that causes chickenpox, results in a painful rash and blisters, with potentially serious complications.

The CDC recommends that people 50 and older get the vaccine, which was approved last fall by the Food and Drug Administration, even if they have had shingles, aren’t sure whether they ever had chickenpox, or previously received the older shingles vaccine, Zostavax. Shingrix is considered better for numerous reasons, but in short it offers much stronger protection than Zostavax, which was licensed in 2006.

No one knows how much immunity a single shot provides because “it wasn’t studied as a one-dose vaccine,” Clements says. Both doses are identical, he says.

Shingrix is covered by most insurance drug plans, including Medicare Part D. The vaccine’s wholesale price is $140 per dose, but patients without insurance coverage will be paying more than that, sometimes as high as $200 or more for each shot after administration fees are added.

Most insurance plans that cover drugs require you to use a “preferred” pharmacy in their network if you want the lowest co-pay. And Clements points out that under the Affordable Care Act marketplace plans the copay could be zero. But what if drugstores in your network don’t yet have the vaccine even though out-of-network pharmacies do? Must you spend additional dollars — potentially a lot of them — because of a situation that isn’t your fault? The short answer: It depends on your plan. You’ll have to call your insurer and ask.

I called Aetna, the parent of my plan (Aetna Coventry), to run some of these questions past Terri Swanson, the company’s vice president and head of Medicare Part D. Aetna will cover the injections whether given in a doctor’s office or at a pharmacy, but the extent of coverage depends on a person’s particular plan. For non-network pharmacies, “Aetna will pay the cost share in effect for that pharmacy,” she says.

My co-pay at a “preferred” pharmacy is $47 for each injection, but I’d pay more if I went to a non-network drugstore or to my doctor.

Patients can obtain the injections either from their physicians or at a drugstore, again depending on their plan. My doctor, for example, recommends — for the lowest cost — getting the shot at a pharmacy, or — he will provide a prescription — getting the vaccine at a drugstore and bringing it to his office, where he will administer it. Because they administer the shots right there, my CVS didn’t even require a prescription for anyone 50 and older.

Payment questions aside, don’t panic: More vaccine is on the way.

“We are shipping large volumes of Shingrix every two to three weeks and expect this schedule to continue for the remainder of the year,” Clements says. “While patients may find their provider or pharmacy is temporarily out of stock, they should check back often or ask the pharmacy to contact them when they are restocked. Going forward, providers and patients can feel confident that more doses are being made available regularly and that they will be able to find the vaccine to complete their two-dose series.”

Much of the vaccine is distributed through wholesalers and distributors, so it can take a week to 10 days for the product to reach pharmacies and doctor’s offices. People can go to shingrix.com/shingles-vaccine-locator.html to find providers and drugstores that have the vaccine in stock. The page is refreshed periodically, but it’s a good idea to call ahead to verify that the location you prefer does, in fact, have it.

Dieffenbach finds it encouraging that more vaccine is en route. She also is relieved that she can wait beyond the end of August — if she has to — to get her second shot. “But I also realize that it may be somewhat challenging to find someplace with the vaccine in stock, since the demand for whatever comes in will undoubtedly be high,” she says.

My CVS called me on a Sunday to say that the store had received a limited shipment of the vaccine. The pharmacists there planned to offer injections initially only to those needing a second dose and only to people who received their first shot at their store. If any vaccine was left after two weeks, it would be available to anyone who wanted it. I wasted no time. Within the hour, I was fully vaccinated.