The UK’s largest pharmaceutical producer, GlaxoSmithKline (GSK), is investing $100 million at its US vaccines production site in Hamilton, Montana, to enable an increase in output of its top-selling shingles vaccine Shingrix and profit from overwhelming US demand.

GSK produces the adjuvants used in several of its vaccines at the Montana site, where the expansion will add jobs to the existing workforce of around 200 people.

“By expanding the adjuvant system production capabilities in Hamilton, we will continue to deliver long-term and sustainable supply for key vaccines, including Shingrix,” said Jack Bailey, president of pharmaceuticals at GSK in the US.

Following its US launch in late autumn 2017, Shingrix, a non-live, recombinant vaccine to help prevent shingles (herpes zoster) and its complications, pulled in sales of $1 billion in 2018, and supply began to run short. As a result, the company was forced to delay TV advertising and put pharmacies on allocation.

As per the end of 2018, more than 8.5 million doses had been shipped, and the drugmaker told a US pharma journal that it plans to ship a “significantly higher” number of doses during 2019. Nevertheless, market watchers said the shortage is could well persist throughout the year.

Up to the end of last year, Shingrix had only been launched in the US and Canada, but the company said it was is in the process of building capacity to support rollouts in other markets. In the US, the vaccine, quickly captured a 99% share of the market, as it is generally regarded to be more effective than the long-time standard Zostavax made by Merck & Co.

Commenting on the demand surge earlier, GSK explained that US vaccine advisers were recommending the injections – assembled in Belgium – for people age 50 and older. This would give the manufacturer a target population of 115 million adults.