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Heart concerns halt Acambis trials

Published on 15/04/04 at 06:01pm

UK biotech Acambis has suspended Phase III clinical trials of its smallpox vaccine after three patients suffered a heart inflammation problem.

Alleged cases of serious side effects - inflammation of the heart and surrounding tissues known as myopericarditis - mean the company could take up to three months to investigate the cases linked to Acambis' ACAM2000 and comparator drug Dryvax.

A company spokesperson said it could not confirm that two cases had been linked to Dryvax and only one to its drugs, although similar cases have been observed in Dryvax and other smallpox vaccines before.

Recruitment of additional volunteers into the trials as well as vaccinations have been suspended pending further reviews, while volunteers will continue to be monitored.   

Two Phase III trials were being carried out by Acambis and have subsequently been halted, where the ratio of individuals receiving ACAM2000 and Dryvax was 3:1. The first trial involved subjects that had never before received smallpox vaccine, while the second involved ones that had been vaccinated previously.

Three incidences of heart inflammation were identified in the first Phase III trial, while the second saw no cases of myopericarditis present in 1,752 vaccinated individuals.

The company says additional, smaller studies involving both ACAM2000 and Dryvax resulted in the identification of another two possible cases of myopericarditis and had been suspended as a precautionary measure.

All cases are being investigated and followed up, with the company's independent Data and Safety Monitoring Board recommending suspension pending review and the obtaining of additional data. The company stated in a release that it was "difficult to determine whether the three recent cases suggested a higher frequency of cardiac adverse events than expected from previous recent experience".

Acambis chief executive Gordon Cameron said the investigation could delay the issue of a product license in the US, but would not affect the company's contract with the US government to supply a stockpile of 200 million doses of the vaccine.

Because of fears of a potential bioterrorist attack the US government has overlooked its usual licensing system for ACAM2000 - Acambis simply has to provide evidence that ACAM2000 is no worse than Dryvax.




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