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The US health regulator did not find any misconduct at clinical sites managed by Care Access for Pfizer and French partner Valneva's trial of a Lyme disease vaccine candidate, the contract research firm said on Wednesday.
Pfizer and Valneva said in February they will stop testing the vaccine in roughly half of US patients in a late-stage study, due to a breach of clinical trial guidelines by a third-party contractor.
The companies at the time did not disclose the name of the contractor or the number of affected patients.
The vaccine for Lyme disease, which causes infections that are transmitted to humans through ticks, has shown a "strong immune response" in a mid-stage study in both children and adolescents a month after a booster dose.
Care Access, which manages more than 150 research sites, said on Wednesday that Pfizer's study was discontinued in over 3,000 participants at the contract research firm's sites earlier this year.
The Boston-based company denied allegations of breach of clinical trial guidelines, and said the US Food and Drug Administration's inspection did not result in any Form 483 observations at its sites.
The FDA's Form 483 is issued to notify a firm after an inspection when an investigator has observed conditions that result in violations.
Pfizer and Valneva did not immediately respond to Reuters requests for comments.