Demand for Pfizer's Covid vaccine could bolster its revenues for years, the US drugs giant has said. Pfizer said it was expecting "durable demand" for the vaccine, in a similar way to flu vaccines. In the first three months of 2021, the vaccine generated revenues of $3.5bn (£2.5bn) as governments scrambled to try to contain the pandemic. Revenue from the treatment is expected to hit $26bn this year - accounting for more than one third of Pfizer's sales. The forecast is based on already-signed contracts for 1.6 billion vaccine doses to be delivered this year. Pfizer said it expected to sign more deals this year, and was in supply talks with several countries for 2022 and beyond. "Based on what we've seen, we believe that a durable demand for our Covid-19 vaccine - similar to that of the flu vaccines - is a likely outcome," said chief executive Albert Bourla. The two-shot vaccine was Pfizer's top-selling product in the first quarter. Expenses and profit from the vaccine are split 50-50 between Pfizer and its German partner BioNTech. Pfizer and fellow US firm Moderna profit from their vaccines, while AstraZeneca and US giant Johnson & Johnson are supplying theirs at cost price while the pandemic continues. Pfizer recently signed a contract with the UK to supply 60 million additional doses in 2021. It is testing the use of a third dose of its vaccine as a booster, and expects the US to give the go-ahead for it to be used in children between 12 and 15 years old during the pandemic. It is also testing the safety and efficacy of the vaccine in children from six months to 11 years old, it said in a prepared statement.