Pfizer's early Vyndaqel launch numbers are off the charts. Should Alnylam be worried?

Launch of Pfizer’s Vyndaqel franchise has blown industry watchers’ estimates out of the water, putting more pressure on potential rival Alnylam Pharmaceuticals.

In its first full quarter after FDA approval to treat ATTR cardiomyopathy, Vyndaqel (tafamidis) collected $79 million in third-quarter U.S. sales, way above the Street’s consensus of $21 million. Worldwide, the drug brought in $156 million.

That outperformance surprised even SVB Leerink analyst Mani Foroohar, who caught an early whiff of success based on electronic medical record data.

“Given the quicker-than-expected ramp, Vyndaqel sales in the U.S. will probably land at the high end of our sensitivity analysis in the $228 million to $250 million all signs point to successful market-building and a substantial opportunity for TTR-CM in the U.S.,” Foroohar wrote in a Wednesday note to clients.

Evercore ISI analyst Umer Raffat pointed to the number of patients diagnosed and the pace of diagnosis as “the big news.”

Pfizer and its investors know that Vyndaqel’s success depends on the Big Pharma’s ability to drive awareness of the condition and hence its currently meager diagnosis rate.

According to CEO Albert Bourla during a Wednesday conference call, about 4,100 commercial patients had been diagnosed as of August 31. Of them, about 2,600 patients had received a prescription for Vyndaqel and about 1,300 had started using the drug.

RELATED: Pfizer's new Vyndaqel franchise worth far more than $1.5B, analyst figures

That number translates into a diagnosis rate of about 4%, according to Angela Hwang, Pfizer Biopharmaceuticals Group’s president. That’s already more than double the 1% to 2% before Vyndaqel’s approval but obviously far from ideal.

For most rare diseases, diagnosis rates can reach 30% to 50%, which informs Pfizer’s blockbuster-level peak estimates for Vyndaqel. “However, we are learning a tremendous amount every single day about this particular disease, about what it takes to diagnose it. Certainly we are focused on making sure that we can do better than that for our patients,” Hwang said.

To help physicians “suspect” the disease, Pfizer has created a list of red-flag symptoms. “From there, we have been educating around the use of scintigraphy as a non-invasive means to diagnose ATTR-CM,” Hwang said. Rather than genetic testing being the key to diagnosis—as the Street was expecting—Pfizer estimates that about 90% of Vyndaqel patients were diagnosed via scintigraphy, a radiographic imaging technique.

RELATED: Pfizer has big growth projections post-Upjohn. But can it actually get there?

As Pfizer cheers its rapid Vyndaqel launch, Foroohar sees “a challenging setup” for Alnylam’s Onpattro, which is approved to treat ATTR poluyneuropathy (PN), a different disorder driven by the ATTR gene. But Onpattro's also in trials for ATTR-CM, where would go head-to-head with Vyndeqel. Pfizer, meanwhile, is gunning for an ATTR-PN approval, too.

On Thursday, Alnylam reported worldwide Onpattro sales of $46.1 million—largely in line with consensus of $45.5 million—with $33.6 million of that coming from the U.S. Though the RNAi drug's U.S. sales marked 19% growth quarter-over-quarter, it’s obviously far behind Vyndaqel.

Playing catch-up in ATTR-CM, Alnylam has started Onpattro's phase 3 Apollo-B study, aiming for a label expansion around 2021 to 2022, the company’s R&D chief, Akshay Vaishnaw, said on a Thursday earnings call.

The company also has vutrisiran, which is moving through a phase 3 study dubbed Helios-A for hATTR polyneuropathy, and headed for a Helios-B study in inherited and wild-type ATTR-CM.

If successful, that follow-up drug could pose a convenience advantage; it’s a quarterly subcutaneous injection. In comparison, Onpattro is an intravenous infusion given once every three weeks, oral Vyndaqel requires once-daily dosing and Ionis’ rival Tegsedi comes as a subcutaneous injection once weekly.