Why did CSL's stock plunge to a 2017 low, and what was the immediate catalyst?

CSL's stock plunged to its lowest level since late August 2017 due to the U.S. Department of Defense's reversal of its long-standing flu vaccine mandate for military personnel — a decision that removed a key institutional demand source for CSL’s influenza vaccines supplied through its unit CSL Seqirus. This move acted as a 'meaningful catalyst for the sell-off' amid pre-existing pressures, including falling U.S. flu vaccination rates, weaker Seqirus earnings, delayed strategic plans, and a broader earnings slump.

How significant is the U.S. market and the flu vaccine business to CSL’s overall revenue and profitability?

The United States is CSL’s largest revenue source, and its vaccines business — particularly influenza shots from CSL Seqirus — is one of its most profitable divisions; Seqirus generated $2.17 billion in fiscal 2025, representing about 14% of CSL’s total revenue. The company is therefore heavily exposed to U.S. policy shifts like the Pentagon’s mandate reversal, which directly threatens demand from a major institutional buyer.

CSL Stock Plunges to 2017 Low Following U.S. Military Flu Vaccine Mandate Reversal

Apr 22, 2026

Australian biotech CSL shares hit 2017 lows after the U.S. military scrapped its flu vaccine mandate, threatening revenue from its key Seqirus division amidst ongoing earnings struggles.

reuters

2026-04-22

CSL Stock Plunges to 2017 Low Following U.S. Military Flu Vaccine Mandate Reversal

CSL Stock Plunges to 2017 Low Following U.S. Military Flu Vaccine Mandate Reversal

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