Altimmune enters the back half of May with its highest-conviction clinical catalyst in years, yet short sellers have barely flinched — a striking standoff between data momentum and a deeply entrenched bear camp.
Short interest commands the centre of this story. At 34.6% of the free float, it has climbed roughly 21% over the past month — the bulk of that jump arriving in a single step between May 8 and May 11, when estimated short shares leapt from ~31 million to ~36 million. That structural shift has held through the current week, with only a marginal 1% pullback on the week. Days to cover runs close to five, per FINRA's most recent fortnight print. The ORTEX short score, at 75.5, sits in the top quartile of all scored names, underscoring just how aggressively positioned the bear camp remains even as clinical news flows favourably.
The lending market tells a more nuanced story. Despite the heavy short load, availability is loose rather than tight: shares still available to borrow equal roughly 157% of current short interest, down only mildly from 170% a week ago. Cost to borrow has eased about 15% over the week to roughly 0.42%, and has fallen nearly 20% over the past month. In other words, there is no squeeze pressure building from within the borrow market. Bears are well-supplied, which likely explains why the elevated short base has proved so sticky even as the stock recovered 7% on the week.
The catalyst creating that tension arrived on May 27. Altimmune released new Phase 2b data from the IMPACT trial at the EASL Congress 2026, showing pemvidutide delivered concurrent improvements across multiple non-invasive markers and measurable fibrosis regression in MASH patients. This is precisely the data point bulls have been waiting for: the bear case centred on regulatory uncertainty in a space where no MASH drug has yet cleared the FDA. The IMPACT readout does not resolve that regulatory risk, but it materially strengthens the Phase 3 rationale and the company's negotiating position with regulators. With approximately $340 million in pro-forma cash, Altimmune has the runway to pursue Phase 3 without near-term dilution pressure — the single most credible pillar in the bull thesis.
Options traders are positioned decisively on the upside. The put/call ratio is at its lowest reading of the past year — 0.069 against a 52-week high of 0.588 — and running more than one standard deviation below its 20-day average. That is an unusually clean call-side lean for a clinical-stage name. The direction aligns with the analyst consensus, which is uniformly bullish: five Buy-rated analysts, no Holds or Sells, with a mean price target around $16 against a current price near $2.93. Both HC Wainwright and Citizens cut targets this month following Q1 results — to $20 and $11 respectively — but neither firm abandoned their constructive ratings. At the $2.93 handle, the return implied by even the lowest published target is substantial. Note that the gap between current price and analyst targets is unusually wide, which reflects genuine optimism about the pemvidutide pipeline rather than stale estimates.
Institutional interest has also been notable. Deep Track Capital reported a fresh 9.98% stake (~19.4 million shares), TCG Crossover Management filed a new 10 million-share position, and Viking Global and RA Capital each disclosed new 5%+ holdings — all reported in late April. BlackRock and State Street both added materially in the same period. Insider activity corroborates the constructive tone: in early April, both the CEO and CFO made open-market purchases at prices around $3.14–$3.41, adding to similar purchases made in early March. These are relatively modest in dollar terms, but the clustering of executive buying near current levels is a meaningful signal in a name this small.
The history from the May 13 Q1 earnings report is a reminder of the stock's two-sided nature: shares fell 5% the day of the print and 8% over the following five days. The EASL presentation is a different kind of event — a pure clinical data release rather than a financial disappointment — and the options and peer market both suggest traders are treating it as an inflection point. Peers GALT and EDIT each rallied more than 20% on the week, and CABA added 13%, pointing to broad appetite for clinical-stage biotech risk this week.
The next scheduled catalyst is Q2 earnings, flagged for August 7. Between now and then, the degree to which this week's EASL data shifts short sellers' conviction — or prompts institutional buyers to push position sizes further — will define whether the 34% short float begins to unwind or simply persists as a persistent counterweight to the clinical story.
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