USA — Pfizer and Valneva are dropping roughly half of the 7,000 total participants enrolled in the Phase III trial of the experimental Lyme disease vaccine VLA15 in the U.S. due to potential Good Clinical Practice violations at certain clinical trial sites run by a third-party site operator.

Pfizer has confirmed that these issues were related to the study’s conduct and not due to any safety concerns with the vaccine, and the study continues to enroll new participants at sites not operated by the third party.

The Phase III trial of the Lyme disease vaccine VLA15 was designed to test its efficacy, safety, and immunogenicity in around 18,000 healthy people, with 7,000 enrolled so far.

Pfizer hopes to file for regulatory approval of VLA15 in the US and Europe in 2025. VLA15 is designed to target the outer surface protein A (OspA) of Borrelia and covers six serotypes prevalent in North America and Europe.

The trial involves participants across Europe and the United States, where Lyme disease is highly endemic.

The VLA15 is a three-dose vaccine. The first shot would be given in the first two months, another between five and nine months, and a booster shot roughly a year later.

Lyme disease is a bacterial infection spread by infected ticks and is the most common disease transmitted by ticks, mosquitoes, or fleas in the U.S., with around 30,000 people affected annually.

Lyme disease can present itself in various ways, with the hallmark sign of early localized disease being a circular red rash called “erythema migrans.”

If left untreated or undiagnosed, the disease can progress to more serious organ involvement, affecting systems such as the heart (cardiac conduction abnormalities), nervous system (cranial nerve palsy), and joints (arthritis).

The incidence of Lyme disease is on the rise worldwide, with the United States alone reporting approximately 16,000 cases in 1996, compared to over 33,000 cases in 2018.

This trend is mirrored in other parts of the world, including Asia, Europe, and North America. The expansion of Lyme borreliosis is also being observed at higher altitudes and latitudes.

This increase has been associated with the disease’s spread into contiguous regions of Canada, with predictions that this northward expansion will continue.

Climatic changes such as temperature and precipitation alterations are expected to contribute to the spread of the tick vector into new and different areas, especially in the northward direction.

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