Doctors worry Shingrix side effects will put patients off their second dose

GlaxoSmithKline's Shingrix carries harsher side effects—but better protection against shingles—than Merck's older Zostavax. (GSK)

The CDC has urged people 50 and older to get GlaxoSmithKline's new shingles vaccine to protect against a notoriously painful condition. But amid the company's important launch, some doctors are worried patients won't return for their second dose if they experience side effects.

Speaking with the U.S. News & World Report, geriatrician Arthur Hayward, M.D., said he heard concerns at a recent medical meeting that some patients will hesitate to return if they experience side effects.

According to Shingrix's FDA label, 78% of vaccine recipients experienced pain at the injection site in clinical tests. Thirty-eight percent experienced redness and 25.9% experienced swelling. Other adverse reactions include muscle pain in 44.7% of recipients, fatigue in 44.5% of recipients, and headache in 37.7% of recipients, according to the FDA. A smaller number of recipients experienced shivering, fever and gastrointestinal symptoms.

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A CDC official told the publication that 1 in 6 recipients had side effects severe enough to keep them from their normal activities.

But the side effects were typically mild to moderate and lasted two to three days, according to the FDA, while the vaccine provides strong protection against a condition that can cause pain for weeks. And, in some instances, shingles can lead to postherpetic neuralgia, or longer-term nerve pain that can persist for years.

GlaxoSmithKline has already implemented physician education efforts to help doctors set patient expectations for the vaccine, a spokesman said. He added that in clinical trials, more than 94% of participants completed the Shingrix series.

"Setting expectations for providers and patients about the potential reactions helps frame their experience," GSK's representative said via email. "GSK is proactively educating healthcare providers and patients and providing tools and resource materials to help facilitate that discussion."

Shingrix launched last year and has replaced Merck's Zostavax on the CDC's list of recommended vaccines. Zostavax's label says 53.9% of patients experienced local pain, 48.1% experienced erythema and 40.4% experienced swelling, among other side effects.

With the preferential recommendation for Shingrix over Zostavax, GlaxoSmithKline is in the midst of introducing a product executives believe could generate $600 million in sales this year.

RELATED: GlaxoSmithKline boosted Shingrix educational efforts after seeing administration, storage errors in launch

In clinical studies, investigators found that Shingrix is more than 90% effective against shingles in people 50 and older. GSK has also reported that the vaccine is effective for people who've previously received Zostavax, and that it provides at least four years of protection. Merck has reported an overall efficacy figure of 51% for Zostavax in people 60 and older.

Since the Shingrix launch, the CDC has noted some administration and storage errors likely connected to the switchover from Zostavax. In response, GSK boosted its physician education efforts.

Editor's note: This story was updated with a statement from GlaxoSmithKline.