Primary objective: To evaluate the safety and immunogenicity of low-dose ID S-OIV H1N1 vaccines delivered via a novel microneedle device (MicronJet600) and compare this to the full-dose standard IM injection.

Hypothesis: Low dose (20%) intradermal (ID) S-OIV H1N1 vaccine delivered via a novel microneedle device (MicronJet600) is equally effective as full-dose standard intramuscular (IM) vaccine.

This is a prospective randomised, single-blinded trial in Queen Mary Hospital. We aim to recruit 200 subjects [with a minimum of 80 subjects per age group (21-65 with chronic diseases and age 65+)] who would be qualified for the Hospital Authority (HA)/ Centre for Health Protection (CHP) Mass Vaccination Program for S-OIV H1N1. These patients include all elderly at the age of 65 or above and all adult patients at the age of 21 or above with chronic illness. Subjects will be randomly assigned to receive either the full-dose (1 dose) standard Panenza vaccine at day 0 (15ug non-adjuvanted monovalent influenza A(H1N1) 2009 vaccine) delivered intramuscularly using a conventional needle (IM group) or a low-dose (1 dose) intradermal injection of Panenza vaccine at day 0 (3ug non-adjuvanted monovalent influenza A(H1N1) 2009 vaccine) delivered with the MicronJet600 (ID group).

Inclusion Criteria:

• All participants qualified for the HA/ CHP Mass Vaccination Program for S-OIV H1N1 as stated above: including all elderly at the age of 65 or above and all adult patients at the age of 21 or above with chronic illness including hypertension, diabetes mellitus, ischemic heart disease, cerebrovascular disease, thyroid disease and chronic renal failure.
• All patients give written informed consent.
• Subjects must be available to complete the study and comply with study procedures.
• Willingness to allow for serum samples to be stored beyond the study period, for potential additional future testing to better characterize immune response.

Exclusion Criteria:

• Clinically significant immune-related diseases, significant recent co-morbidities and pregnant volunteers.
• Inability to comprehend and to follow all required study procedures.
• History or any illness that might interfere with the results of the study or pose additional risk to the subjects due to participation in the study
• Have received an S-OIV H1N1 vaccination.
• Have a recent (starting May 2009) history (documented, confirmed or suspected) of a flu-like disease).
• Have a known allergy to eggs or other components of the Study Vaccines (including gelatin, formaldehyde, octoxinol, thimerosal, and chicken protein), or history of any anaphylaxis, serious vaccine reactions, to any excipients.
• Have a positive urine or serum pregnancy test within 24 hours prior to vaccination, or women who are breastfeeding.
• Female of childbearing potential, not using any acceptable contraceptive methods for at least 2 months prior to study entry or that do not plan to use acceptable birth control.