UK biotechnology company Acambis said this morning that its candidate smallpox vaccine MVA3000 generated a fourfold increase in neutralising antibodies against the virus in more than three quarters of patients enrolled in a Phase II study.

The results are good news for Acambis and development partner Baxter, which are hoping to win a lucrative contract from the US government for supplying smallpox vaccine for use in people who cannot use the traditional shot, such as the elderly, patients with immune disorders and skin conditions such as eczema. Persons suffering from eczema are in a high-risk group to develop a life-threatening side-effect after vaccination with traditional replicating smallpox vaccines.

In the 590-patient study, up to 75% of patients who had not received prior vaccination against smallpox developed a four-fold increase in neutralising antibodies against the virus after two doses. Meanwhile, in patients already vaccinated for smallpox, 88% achieved this endpoint.

Acambis has already been awarded two contracts by the US National Institute of Allergy and Infectious Diseases (NIAID) for the manufacture and development of MVA3000, which is based on the Modified Vaccinia Ankara technology. The first contract, awarded in February 2003, was for $9.2 million. The second, awarded in September 2004, was worth $76 million and required clinical testing and manufacture of 500,000 doses of MVA3000.

Acambis and Baxter are going head-to-head in this endeavour with rival vaccine company Bavarian Nordic, whose own MVA-based smallpox vaccine – Invamune, is also in Phase II testing. Bavarian Nordic also supplied 500,000 doses of its vaccine to the NIAID.

The US government is currently deliberating how to organise a supply of 20 million doses of smallpox vaccine for people who cannot tolerate the current products, such as Dryvax, with one or both companies potentially standing to benefit from a contract.

Acambis filed an initial response to this contract offer in October 2005, but since then the USA has issued an amendment to the tender which revises the preclinical and clinical testing requirements, following guidance from the US Food and Drug Administration. It also extends the delivery period for usable MVA vaccine from 24 months to 60 months from contract award. Last week Acambis said the delay would cause it to miss its earlier full-year financial guidance.

In the meantime, Acambis and Bavarian Nordic are locked in litigation over ownership of the rights to the MVA technology used in their products. The International Trade Commission is due to rule in the case later this month.