Pfizer Inc. PFE -0.82% expects sales for its Covid-19 vaccine this year to reach about $33.5 billion, up nearly 30% from its forecast three months ago, as the shot plays a growing role in global efforts to curb the spread of the coronavirus.

With concerns rising over the highly infectious Delta variant, Pfizer also said that booster shots would likely be needed to ensure protection against the virus.

U.S. officials haven’t authorized the use of booster shots, although they are studying the issue. Pfizer and partner BioNTech SE plan to seek regulatory approval in the U.S. for a booster shot in August. A clinical trial testing an updated version of its vaccine targeting the Delta variant is also set to start next month, the company said Wednesday when announcing second-quarter earnings.