Pfizer and Valneva said on Monday their Lyme disease vaccine showed more than 70% efficacy in a late-stage study, even as it missed its main goal.

U.S.-listed shares of the French drugmaker tumbled more than 35% in premarket trading following the update, while Pfizer was flat.

The vaccine demonstrated 73.2% efficacy starting 28 days after the fourth dose in reducing confirmed Lyme disease cases, compared to the placebo.

However, fewer-than-anticipated Lyme cases during the study led to the trial falling short of the key requirement that the vaccine should still be at least 20% effective even in the worst-case scenario. In the first analysis, it came in lower, at 15.8%.

A second planned analysis met the bar, though with 74.8% efficacy, adding to Pfizer's confidence "in the vaccine's potential," as it plans "submissions to regulatory authorities."

There is no approved vaccine to prevent Lyme disease - spread by bites from infected blacklegged ticks - after GSK discontinued its Lymerix shot in 2002, citing insufficient demand.

Symptoms include fever, headache, fatigue, and a skin rash called erythema migrans, according to the U.S. Centers for Disease Control and Prevention. If left untreated, infection can spread to joints, the heart, and the nervous system.

Most cases of Lyme disease can be treated successfully with a few weeks of antibiotics.

The CDC estimates about 476,000 people are diagnosed and treated for Lyme annually in the U.S., while roughly 132,000 cases are reported each year in Europe, the companies said.

Last year, Valneva said it expects Pfizer to launch the vaccine in the second half of 2027 following approval.