By Bhanvi Satija and Sriparna Roy

(Reuters) -Pfizer lifted its annual earnings forecast on Wednesday and reported a first-quarter profit above Wall Street estimates, boosted by cost cutting efforts and stronger-than-expected sales of its COVID antiviral treatment.

Sales of Padcev, a treatment for advanced bladder cancer Pfizer gained through its $43 billion deal for Seagen, also came in ahead of analysts' expectations.

The Seagen deal, as well as its $4 billion cost-cutting plan, are a key part of Pfizer's post-COVID growth strategy. Investors have also been tracking the performance of the company's new RSV vaccine, which has been trailing a rival shot from GSK since they both launched last year.

The company raised both ends of its 2024 profit forecast range by 10 cents - less than the first-quarter beat - and now expects to earn $2.15 to $2.35 per share. Shares of the New York-based drugmaker, which have lost 11% of their value this year, rose about 4% to $26.65 in morning trade.

"I think investors have become so accustomed to disappointments that a solid quarter and an upgrade were always going to be well received," said Derren Nathan, analyst at Hargreaves Lansdown.

Seagen's targeted cancer therapies Padcev and Adcetris brought in combined sales of $598 million in the quarter for Pfizer, although Adcetris sales fell short of analysts' expectations.

Sales of Abrysvo for protection against respiratory syncytial virus (RSV) were $145 million, short of the $353.3 million expected by analysts.

"It would be good to see an acceleration for Abrysvo," Nathan added. "The $145 million feels disappointing. GSK’s Arexvy seems to be gaining acceptance at a quicker rate."

Earlier on Wednesday, GSK said Arexvy sales were 182 million pounds ($227.26 million) in the first-quarter, more than 80% of which came from the United States. GSK said an "overwhelming majority of doses" were administered in the retail setting.

Arexvy currently owns two-thirds of the new RSV vaccine market.

Pfizer said it still expects $8 billion in combined sales of its COVID-19 products, the vaccine Comirnaty it shares with BionTech and oral antiviral Paxlovid.

Paxlovid sales dropped 50% to $2.04 billion for the quarter, but came in well above the $762.5 million analysts had expected.

Pfizer last year renegotiated a U.S. contract, allowing the government to return unused Paxlovid inventory. It recorded a $771 million favorable adjustment in the quarter, related to the U.S. government return of some treatment courses.

The $771 million adjustment to the estimated revenue reversal of $3.5 billion last quarter reflects 1.4 million fewer treatment courses returned by the U.S. government through Feb. 29, 2024 versus the estimated 6.5 million expected, a Pfizer spokesperson said.

Sales of the COVID vaccine fell 88% to $354 million, missing estimates of $496.5 million.

Prevnar pneumonia vaccines were a bright spot, taking in sales of $1.69 billion that beat estimates of $1.66 billion.

Pfizer posted an adjusted profit of 82 cents per share, topping analysts' expectations by 30 cents, according to LSEG data.

(Reporting by Bhanvi Satija and Sriparna Roy in Bengaluru and Patrick Wingrove in New York; Editing by Arun Koyyur and Bill Berkrot)