Demand for the two-dose Shingrix vaccine has skyrocketed since it became broadly available in the United States in the spring. The new vaccine provides much greater protection than an older, single-shot vaccine from a disease that affects one in three adults, and can cause debilitating nerve pain that can last months, or even years. Demand is surging because federal health officials last year recommended it for healthy adults at age 50, a decade earlier than previous recommendations. Federal health officials also urged it for people who have had shingles, as well as those who received the old vaccine, or have had or are unsure if they have had chickenpox. Those recommendations took British drugmaker GlaxoSmithKline by surprise, leaving it scrambling to keep up with demand, say company representatives.

Company officials estimate about 115 million people in the United States, who are 50 and older, are eligible for the vaccine. Shingles, a painful condition that causes blisters, occurs when the chickenpox virus resurfaces decades later. There are an estimated 1 million cases of shingles each year in the United States; the risk of the disease increases as people age.

“All I want for Christmas is for my pharmacy to get some Shingrix,” tweeted one woman earlier this week.

Consumers have been searching for pharmacies with Shingrix doses on neighborhood listservs, in postings on social media, and in visits to pharmacy after pharmacy. A Pennsylvania man wrote on Facebook a week ago that his wife was told by her local supermarket pharmacy that the waiting list was about 12 months. A CVS pharmacist in Gaithersburg, Maryland, and a Walgreen’s pharmacist in downtown Washington, D.C. said this week that they hadn’t received any shipments since August.

“It’s worse now,” said a pharmacist at Walgreen’s, who declined to give her name because she wasn’t authorized to speak to reporters. The pharmacy is not keeping a waiting list because “there’s no promise of when it’s going to come out again.”

“As soon as they get it in, it’s going out pretty quick,” said Michael Rothholz, chief strategy officer for the American Pharmacists Association.

Pharmacies began offering the vaccine broadly in mid-March. By May, the Centers for Disease Control and Prevention was reporting shortages. Since the spring, drugstore chain CVS has had difficulty keeping an ample supply across the chain’s 9,800 stores and more than 1,100 clinics because of limited supply from the manufacturer, said spokeswoman Amy Lanctot.

Shipments arrive about every three weeks, she said. The supply “did get a little better in the fall,” she said. But since then, it has gotten worse, she said. “It’s just not being made in the amounts that are needed.”

Complicating the situation is the recommendation for consumers to get their second dose within two to six months of the first. Many consumers are struggling to find their second dose. Pharmacies are supposed to give priority to those patients. Some pharmacies are requiring consumers to get their second dose at the same place they got their first shot. Others will give the second shot if consumers show proof they have gotten the first one, regardless of where.

Consumers are understandably confused.

A woman who got her first shot in Del Ray Beach, Florida, in August was searching for her second in Brooklyn this week. “None to be found anywhere,” she tweeted.

The Centers for Disease Control and Prevention says patients who wait longer than six months don’t have to start over. But they should get the second dose as soon as possible because the maximum immunity – more than 90 percent – is based on two doses. Protection stays above 85 percent for at least the first four years after vaccination, the CDC says. GlaxoSmithKline did not study how much immunity is provided by one dose.

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.

Consumers who have gotten the shots, which is given in the muscle of the upper arm, like the annual flu vaccine, say the side effects have included pain, soreness and swelling at the injection site for two to three days, muscle aches and flulike symptoms, headaches and upset stomach. But those side effects pale in comparison to one of the most common and serious complications of shingles, debilitating nerve pain that has no treatment or cure.

GSK directs consumers to its Shingrix locator, but the information is refreshed only once a week. Consumers are urged to contact health-care providers or pharmacies directly for the most up-to-date availability. At CVS, consumers can call pharmacies directly, but not the MinuteClinics, which are separate operations.

Acknowledging growing consumer frustration, CVS in recent weeks gave operators at the MinuteClinic’s patient support center access to the system that allows them to look up Shingrix supply at individual clinics. But the website does not mention the shortage, or inform consumers they can use the toll-free number to look up supply at individual clinics. The Washington Post asked the operator to check availability at 13 clinics within 10 miles of a suburban Maryland Zip code. None had it.

Sean Clements, a spokesman for GSK, said the manufacturer has increased and accelerated supply of Shingrix in the United States, shipping “large volumes” every two to three weeks. Starting in December, Clements said the company will move to a twice-monthly shipping schedule. He declined to provide specifics. A GSK representative from the company’s customer service line said 300,000 doses were shipped in November, and another 160,000 doses were shipped Dec. 3.

The company makes Shingrix at a facility in Rixenstart, Belgium, which is already at maximum capacity, the representative said. It takes six to nine months to produce the vaccine. Although certain elements were produced before the vaccine received approval from the Food and Drug Administration, the company is still playing catch-up, officials said during a briefing on their latest quarterly report in late October.

As of Oct. 1, almost 7 million doses of the vaccine had been administered worldwide since the vaccine’s launch in late November, 2017, with most of it going to the United States. GSK said it distributed as many doses in the third quarter of 2018, as it had in the first six months of the year.

Next year, the company plans to bring “significantly more doses to the United States,” spokesman Clements said. But because health-care professionals will continue to vaccinate at a rate many times that of previous years, the company expects “ordering limits to continue throughout 2019,” he said.

Assuming the 7 million doses administered in 10 months is close to what the company shipped, industry executives estimate the company is making about 700,000 doses a month, or around 8.4 million doses a year. Over the next two to three years, company officials said they plan to increase production annual doses in the “high-teens millions.”

Shingrix has been so successful that GSK executives revised their earlier annual revenue forecast for Shingrix this year from $600 million to about $900 million and nearly $1 billion, according to GSK’s latest earnings report.

“We need to get the supply expanded as fast as possible because we can pretty much sell anything that we make now in the U.S.,” said Luke Miels, president of GSK’s global pharmaceuticals division, during the Oct. 31 earnings call with investment analysts.