FORM 6-K

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                        Report of Foreign Private Issuer

                    Pursuant to Rule 13s - 16 or 15d - 16 of
                      the Securities Exchange Act of 1934

                           For the month of July 2006


                                  Acambis plc
                (Translation of registrant's name into English)

                           Peterhouse Technology Park
                               100 Fulbourn Road
                               Cambridge CB1 9PT
                                    England

                    (address of principal executive offices)

    (Indicate by check mark whether the registrant files or will file annual
                 reports under cover of Form 20-F or Form 40-F

                         Forms 20-F X     Form 40-F

  Indicate by check mark whether the registrant by furnishing the information
     contained in this Form also thereby furnishing the information to the
                Commission pursuant to Rule 12g3-2(b) under the
                       Securities Exchange Act of 1934).

                              Yes       No X

 (if "Yes" is marked, indicate below the file number assigned to the registrant
                   in connection with Rule 12g3-2(b): 82- ).




Enclosure:

Update on MVA procurement


Update on US Government MVA vaccine procurement process


Cambridge, UK and Cambridge, Massachusetts - 26 July 2006 - Acambis plc
("Acambis") (LSE: ACM, NASDAQ: ACAM) provides an update on the US Government
tender process relating to Modified Vaccinia Ankara ("MVA") attenuated smallpox
vaccine.

The Department of Health and Human Services ("HHS") of the US Government is
seeking to procure up to 20 million doses of MVA vaccine and issued a Request
for Proposals No. DHHS-ORDC-V&B-05-06 ("RFP3") in August 2005. Acambis, which is
developing an MVA vaccine in partnership with Baxter Healthcare SA, submitted an
initial response to RFP3 in October 2005 and has submitted further responses
since then as part of the ongoing procurement process.

HHS has issued an amendment to RFP3. This incorporates a revised pre-clinical
and clinical testing requirement, following guidance received from the US Food
and Drug Administration ("FDA"). It also extends the delivery period for usable
MVA vaccine from 24 months to 60 months from contract award. Responses to the
RFP3 amendment are to be provided to HHS by mid-August. Thereafter, it is
expected that Final Proposal Revisions will be requested prior to contract
award(s) being made.

The revised testing requirement received from the FDA also impacts on Acambis'
existing cost-plus MVA contractual activities, resulting in certain activities
previously anticipated for 2006 continuing into 2007. With this change in the
timing of activities and, therefore, revenues, it is expected that "predictable"
revenues overall will be marginally lower than the guidance for 2006 of
GBP20-25m previously provided.

                                    -ends-

Enquiries:

Acambis plc
Gordon Cameron, Chief Executive Officer
David Lawrence, Chief Financial Officer
Lyndsay Wright, VP, Communications and IR
Tel: +44 (0 1223 275 300

Financial Dynamics
David Yates/Anna Keeble
Tel: +44 (0) 20 7831 3113

About Acambis
Acambis is a leading developer of vaccines to prevent and treat infectious
diseases. Recognised internationally as the leading producer of smallpox
vaccines, Acambis is developing an investigational smallpox vaccine, ACAM2000,
and is manufacturing emergency-use stockpiles of this investigational vaccine
for the US Government and other governments around the world. It is also
developing an attenuated smallpox vaccine, MVA3000, under contracts with the US
National Institutes of Health. Acambis' US-based subsidiary Berna Products
Corporation markets Vivotif(R), the world's only licensed oral typhoid vaccine,
in North America. Acambis' investigational vaccine against Japanese
encephalitis, ChimeriVax-JE, is undergoing Phase 3 clinical testing. It also has
the most advanced investigational vaccine against the West Nile virus, which has
spread to 48 US States in the last seven years, and a vaccine against
Clostridium difficile bacteria, a leading cause of hospital-acquired infections.

Acambis is based in Cambridge, UK and Cambridge, Massachusetts, US. Its primary
listing is on the London Stock Exchange (ACM) and its shares are listed in the
form of American Depositary Receipts on NASDAQ (ACAM). More information is
available at www.acambis.com.

"Safe Harbor" statement under the Private Securities Litigation Reform Act of
1995:

The statements in this news release that are not historical facts are
forward-looking statements that involve risks and uncertainties, including the
timing and results of clinical trials, product development, manufacturing and
commercialisation risks, the risks of satisfying the regulatory approval process
in a timely manner, the need for and the availability of additional capital. For
a discussion of these and other risks and uncertainties see "Risk management" in
the Company's 2005 Annual Report and "Risk factors" in its Form 20-F, in
addition to those detailed on the Company's website and in the Company's filings
made with the Securities and Exchange Commission from time to time. These
forward-looking statements are based on estimates and assumptions made by the
management of Acambis and are believed to be reasonable, though are inherently
uncertain and difficult to predict. Actual results or experience could differ
materially from the forward-looking statements.


                                      SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant Peptide Therapeutics Group has duly caused this report to be
signed on its behalf by the undersigned, thereunto duly authorized.



Date: 26 July 2006                           ACAMBIS PLC





                                        By:  /s/ Lyndsay Wright
                                             Name: Lyndsay Wright
                                             Title: VP, Communications and IR.