Pfizer has raised its forecast for sales of the Covid-19 vaccine that it developed with Germany's BioNTech by 28.8% to $33.5 billion, as countries scramble to secure supply of the shots.

The company said the raised sales forecast of the vaccine is based on signed deals for 2.1 billion doses this year, and that it could increase if it signs additional contracts.

Pfizer and BioNTech expect to produce 3 billion doses of the vaccine this year.

Pfizer gained a head start in December with the first US emergency authorization of a Covid-19 vaccine, and has since jumped ahead of rivals that have faced manufacturing hurdles.

J&J last week estimated full-year Covid-19 vaccine sales of $2.5 billion, while Moderna has forecast $19.2 billion.

Pfizer has said it believes a third "booster" dose of its vaccine will be needed in the future, which could help it bring in more sales in 2022.

The company said today it could file for an emergency use authorization for a potential booster dose as early as August.

Top infectious disease official Anthony Fauci said on Sunday that Americans who are immune compromised may end up needing booster shots as the United States deals with increasing cases from the Delta variant of the coronavirus.

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's previous forecast in May of $26 billion was based on deals signed for 1.6 billion doses.

Wall Street was broadly in line with that forecast at $28.51 billion, according to nine analysts polled by Refinitiv.

Expenses and profit from the vaccine are split 50-50 between Pfizer and BioNTech.