Fluarix and Flulaval are being shipped in single-dose, 0.5 mL pre-filled syringes and are not recommended for individuals with severe allergies to vaccine components or a history of Guillain-Barré syndrome.

Shares of GSK rose on Thursday after the company announced it had begun shipping its seasonal flu vaccines, Fluarix and Flulaval, to U.S. pharmacies and healthcare providers, ahead of the 2025–26 flu season.

The stock closed up 1.4% at $39.58 on Thursday, with the stock gaining another 0.5% to $39.79 in after-hours trading.

The company said the rollout follows U.S. Food and Drug Administration (FDA) clearance for licensing and lot release. 

The vaccines, Fluarix and Flulaval, will be offered as single-dose, 0.5 mL pre-filled syringes and are approved for anyone aged six months and older.

This season’s flu shot targets three strains expected to circulate: A(H1N1), A(H3N2), and a B/Victoria lineage virus. 

The CDC continues to recommend that nearly everyone six months and up get a flu shot each year, ideally by the end of October.

The rollout follows what the CDC called the worst flu season in 15 years. 

From October 2024 through May 2025, the virus is estimated to have caused between 47 and 82 million illnesses, up to 1.3 million hospitalizations, and as many as 130,000 deaths.

GSK stated that the vaccines are not recommended for individuals who have had severe allergic reactions to any component or for those with a history of Guillain-Barré syndrome. 

Mild side effects like injection site soreness, fatigue, or headaches are possible.

Separately, GSK scored a legal win this week in the ongoing Zantac litigation. 

The Delaware Supreme Court ruled that expert testimony connecting ranitidine, the drug’s active ingredient, to cancer couldn’t be used in court. The ruling reversed an earlier decision that had allowed approximately 75,000 lawsuits to proceed. 

The court stated that the plaintiffs failed to establish a reliable scientific link between the product and the alleged harms. GSK had challenged the expert evidence alongside Pfizer and Boehringer Ingelheim.

On Stocktwits, retail sentiment for GSK was ‘bullish’ amid ‘high’ message volume.

GSK’s stock has risen 16.6% so far in 2025.

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