GlaxoSmithKline has forecast 2019 sales of its fast-growing shingles vaccine Shingrix to be "significantly" more than £1 billion today as the drugmaker outpaced first quarter forecasts. 

Shingrix, launched in 2017, is an important source of growth for GSK's chief executive Emma Walmsley, as she strives to improve the company's commercial performance after streamlining its operations and spinning off or selling units. 

"Shingrix has delivered another fantastic performance in the quarter," Walmsley told journalists on a GSK results call.

Sales of the treatment for shingles, a viral infection of the skin that causes painful rashes, were £357m in the quarter to the end of March, up 61.5% from the fourth quarter. 

Analysts had expected quarterly sales of £249m and are forecasting 2019 sales of £1.17 billion. 

Shingrix sales were largely driven by the US, which benefited from market growth in new patient populations covered by immunisation recommendations as well as growth in Canada and the drug's recent launch in Germany. 

But sales of the company's asthma treatment Advair, however, fell 15% to £486m in the quarter, due to competition from a generic version. 

Analysts said the Shingrix performance is positive as a key future growth driver, but GSK's pharma unit performance is likely to be perceived as broadly in-line given Advair now faces US generic erosion.

GSK said its turnover rose to £7.66 billion in the quarter, from £7.22 billion a year earlier, and above a company-provided consensus of analysts' forecasts of £7.56 billion. 

Adjusted operating profit was 30.1 pence per share in the quarter, compared to expectations of 26.1 pence per share. 

"We have made a strong start to 2019, which is an important year of execution for GSK, with growth in sales, operating margins and earnings per share in Q1," Walmsley said in a statement accompanying the results. 

FTSE-100 member GSK also said it had decided to stop the clinical development of its next generation strep pneumonia candidate vaccine and the candidate for a universal flu vaccine. 

The company, which reiterated its 2019 forecast of a decline in adjusted earnings of 5-9%, said its quarterly earnings were hurt by continuing pricing pressure and investments in promotions, particularly for new launches.