Pfizer's Lyme disease vaccine shows 70% efficacy despite trial shortfall

Pfizer $PFE plans to seek regulatory approval for a Lyme disease vaccine that reduced infections by more than 70% in a late-stage trial but missed its primary statistical goal, the company said Monday.

The vaccine, co-developed with French drugmaker Valneva, blocked 73.2% of confirmed infections versus placebo — a figure measured beginning four weeks after the final injection. A lower-than-projected number of infections caused the trial to miss its primary requirement — that even a pessimistic statistical reading show at least 20% protection. That floor came in at 15.8% in the initial analysis, according to NBC News. The second pre-specified analysis cleared that bar, recording 74.8% efficacy.

"Lyme disease can cause potentially serious consequences — where individuals and families face symptoms that can disrupt daily life, work, and long-term health — and there is currently no vaccine available," Annaliesa Anderson, chief vaccines officer at Pfizer, said in a statement.

Approval would make it the sole human Lyme disease vaccine on the market. LYMErix, a predecessor vaccine that had demonstrated 76% efficacy at its 1998 approval, was pulled from the market in 2002 after adverse-event reports fueled public concern and cratered demand, according to The Washington Post. A 2006 editorial in the journal Epidemiology and Infection attributed the earlier vaccine's failure largely to public perception of risk, shaped by negative press coverage, rather than evidence of harm found by regulators.

Lyme disease is caused by bacteria spread by bites from infected blacklegged ticks. Early symptoms usually include fever, fatigue, headache, and a bulls-eye rash at the bite. If not treated, the disease can lead to heart inflammation, joint damage, and nerve problems. The CDC estimates about 476,000 Americans are diagnosed and treated each year. Pfizer and Valneva estimate about 132,000 cases annually in Europe.

The study included roughly 9,400 participants, from children as young as 5 to adults. That was down from an original pool of about 18,000 after the companies removed roughly half their participants in 2023 following quality problems at an outside clinical site operator, according to CNBC. The trial data have not been independently reviewed or published in a scientific journal. No safety concerns were observed, the companies said.

The dosing schedule spans two years: three injections in the first year — spaced two months apart for the first two, with the third given between five and nine months after the second — followed by a booster in the second year. Valneva has projected a commercial launch in the latter half of 2027, assuming regulators clear the shot.

Valneva stock fell more than a third in premarket trading on the announcement. Pfizer stock was little changed.