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Pfizer pulls 50% of people from phase 3 Lyme disease study for GCP violations at US trial sites

Pfizer and Valneva’s phase 3 Lyme disease vaccine clinical trial has gone badly wrong. After discovering good clinical practice (GCP) violations at some trial sites, the partners have removed around half of the enrolled participants from the study.

The clinical trial got underway in August with the goal of enrolling around 18,000 healthy people who live in areas with endemic Lyme disease and lead lifestyles that put them at increased risk of being bitten by ticks. Participants are receiving either VLA15 or placebo to assess the ability of the multivalent protein subunit vaccine to reduce the risk of catching Lyme disease.

As of last month, Valneva aimed to complete enrollment for the 6,000-subject primary efficacy readout in the second quarter, putting it and Pfizer on track to file for approval in 2025. Now, the pivotal trial has suffered a serious setback, as Valneva explained in a statement.

“Pfizer, as the study sponsor, has decided to discontinue a significant percentage of participants in the U.S. These study participants, representing approximately half of the total recruited participants in the trial, are being discontinued following violations of GCP at certain clinical trial sites run by a third-party clinical trial site operator,” the French vaccine developer said.

As of an update in mid-December, Pfizer listed 79 study locations, including some that were yet to start recruiting. Fifty-two of the sites were in the U.S., with Valneva previously saying that it expected the U.S. to account for two-thirds of participants.

The clinical trial remains active, and sites other than those operated by the third party are continuing to enroll participants. Pfizer and Valneva could still potentially file for approval in the U.S. and Europe in 2025, “subject to the agreement of these regulatory agencies to proposed modifications of the clinical trial plan.” Pfizer is notifying participants affected by the changes to the study.

Valneva saw its share price drop almost 9% on market open Friday, to 5.80 euros from a Thursday close of 6.33 euros. Analysts at the financial services group ODDO BHF predicted the French company’s stock would take a hit as a result of the trial news.

“At this stage we have zero visibility on how the FDA might react,” the analysts added in a note this morning. “It could, for example, request an additional study over a tick season, which would defer approval by around one year (now our baseline scenario).”