C&W UK declined to comment on the business, but is understood to have been brought in following lengthy discussions between Chiron UK and numerous PR agencies earlier this year.
The firm hit UK headlines last autumn when regulators withdrew its production licence at its flu-vaccine factory near Liverpool following concerns over bacterial contamination. The suspension was lifted in March.
Chiron continues to use Fleishman-Hillard for UK public affairs support.
The agency replaced Lexington Communications at the end of last year (PRWeek, 3 December 2004).
Two months ago Chiron was hit by the departure of policy and corporate affairs manager Clara Bentham to French pharma firm Servier (PRWeek, 20 May).