By Val Brickates Kennedy

Anti-viral developers Gilead Sciences, Roche and GlaxoSmithKline PLC were up significantly in early trading Monday on fears that the swine flu outbreak that started in Mexico could become a global pandemic.

Shares of Gilead (GILD) were up 4% at $47.73, while Glaxo (GSK) shares climbed 6% to $30.96. Roche shares were up 5% to $31.80.

Gilead developed a leading flu-fighter, Tamiflu, also called oseltamivir. The biotech group receives royalties on Tamiflu sales from marketer Roche (RHHBY).

Glaxo, meanwhile, sells a popular flu-fighting agent called Relenza, also known as zanamivir. The product was co-developed with Australian firm Biota Holding Ltd (BTAHF)(BTA.AU), which receives royalties on sales.

Gilead reported last week that it took in $33 million in Tamiflu royalties, down from $93 million the previous year. Gilead attributed the drop to stockpiling by health agencies worldwide in preparation of a possible pandemic of the avian flu virus.

According to Biota's website, Relenza had sales of $462 million for the quarter ended March 31, garnering the company about $32 million in royalties. Biota noted that the U.K. and British governments had recently ordered "significant" amounts of the product as part of their pandemic stockpiling measures.

Lazard Capital Markets analyst Joel Sendek said in his note early Monday that the Centers for Disease Control suspects other flu-fighting agents are ineffective against the swine flu virus and is recommending either oseltamivir or zanamivir to treat patients.

"Gilead is likely a beneficiary of the current situation. We anticipate increased retail sales of Tamiflu as people with suspicious symptoms consistent with the flu are likely to purchase Tamiflu. We also expect additional government stockpiling in the future given the scale and speed of the current swine flu emergency," wrote Sendek, who tracks Gilead.

-Val Brickates Kennedy; 415-439-6400; AskNewswires@dowjones.com