Pfizer Inc on Wednesday raised its forecast for full-year sales of the COVID-19 vaccine that it developed with Germany's BioNTech by nearly 29% to $33.5 billion, as nations stock up on doses for the rest of the year.

The company also said on Wednesday it could apply for an emergency use authorization for a potential booster dose as early as August, reiterating that a booster shot will likely be needed in the future. The raised sales forecast of the vaccine is based on signed deals for 2.1 billion doses, and the company could increase it if it signs additional contracts.

The drugmaker gained a head start in December with the first U.S. emergency authorization of a COVID-19 vaccine, and has since jumped ahead of rivals that have faced manufacturing hurdles. Johnson & Johnson's vaccine has also been under scrutiny over safety concerns. J&J last week estimated full-year COVID-19 vaccine sales of $2.5 billion, while Moderna has forecast $19.2 billion.

Pfizer said it had shipped 1 billion doses of the vaccine to date since December. The companies have a production target of around 3 billion doses this year. "Prior to the pandemic, Pfizer produced approximately 200 million doses annually across our entire Vaccines portfolio," Chief Executive Officer Albert Bourla said in prepared remarks ahead of a conference call.

The production ramp-up is subject to expansion at current facilities, adding new suppliers and contract manufacturers, the company said. The drugmakers plan to test a version of the vaccine to target the fast-spreading Delta variant of the virus in August, with the first batch already manufactured, Pfizer said.

The United States purchased 200 million more doses of the Pfizer/BioNTech vaccine last week to help with pediatric vaccination as well as possible booster shots – if they are needed. Pfizer records most of the combined sales from the vaccine and splits expenses and profit 50-50 with BioNTech.

Pfizer also raised its estimate for full-year adjusted profit to between $3.95 and $4.05 per share, from its prior expectation of $3.55 to $3.65.

Meanwhile,AstraZeneca's COVID-19 vaccine sales more than tripled to $894 million in the second quarter from the previous three months, and the drugmaker updated its 2021 forecasts on Thursday to include sales from its Alexion unit.

The Anglo-Swedish company has also delayed its application to U.S. authorities for approval of the vaccine to the second half of this year. Previously, AstraZeneca was hoping to file it within the first half.

The vaccine, invented by Oxford University and hailed a milestone in the fight against the pandemic, has faced several setbacks, including production delays and possible links to some rare, but severe side-effects that are being probed by regulators.