H5N1 Priming and Boosting Strategies

Severe disease in humans due to avian influenza viruses of the H5N1 subtype has raised concern regarding the potential emergence of these viruses in pandemic form. Results of earlier studies suggest that previous priming can significantly affect the responses to subsequent booster doses, even if these booster doses represent an antigenic variant. Both the length of time between priming and revaccination, as well as the antigenic relatedness of the priming and revaccination antigens, may impact the response. These issues could have an important impact on pre-vaccination strategies prior to the emergence of a pandemic. This study will evaluate immunogenicity with the same or with different H5 variants. In this study, "different" will be defined as clade 1 followed by clade 1, clade 1 followed by clade 2, clade 2 followed by clade 2, or a combination of clades 1 & 2 followed by a combination of clades 1 & 2. In addition, the study will evaluate the effect of the interval between doses on the subsequent response, with "ultra-short" intervals defined as 7 or 14 days, a "short" interval defined as 28 days and a "long" interval defined as 180 days. The study will evaluate whether the use of a longer duration between doses or cross-clade priming will result in enhanced immunogenicity. Primary objectives are: evaluate the dose and schedules of unadjuvanted inactivated subvirion H5N1 vaccines belonging to the same or different clades in H5-naïve, healthy adults; determine if boosting of subjects given the inactivated influenza rg A/Vietnam/1203/04 vaccine with a heterologous antigen inactivated influenza rg A/Indonesia/05/05 results in broader or higher immune responses compared with boosting with the homologous antigen; and evaluate the immune response to 2 doses of H5 vaccine given at times < 1 month apart. Secondary objectives are: determine the safety of 2 doses of inactivated H5 vaccines in healthy adults given at different schedules and antigen combinations; obtain additional information regarding the antibody response to a single dose and to ultra-short immunization schedules; and evaluate the effect on antibody levels after receiving an antigenic variant to the priming virus given as a booster or simultaneously. The study will be conducted as a randomized, prospective controlled, multi-center trial. Approximately 500 healthy adult subjects, aged 18-49, who have no history of prior H5 influenza exposure or vaccination will be enrolled. Subjects will be randomized to receive varying schedules, (2 doses separated by 7, 14, 28 or 180 days), and clades of unadjuvanted inactivated subvirion H5N1 vaccine.

Inclusion criteria

• Men and women, 18 through 49 years old, who deny exposure to H5 virus or participation in an H5 vaccine study.
• In good health, as determined by vital signs (heart rate less than 100 bpm; blood pressure: systolic less than or equal to 140 mm Hg; diastolic less than or equal to 90 mm Hg; oral temperature less than 100.0 degrees Fahrenheit), medical history to ensure stable medical condition and a targeted physical examination, as indicated, based on medical history. A stable medical condition is defined as no recent change in prescription medication, dose, or frequency of medication in the last 3 months and health outcomes of the specific disease are considered to be within acceptable limits in the last 6 months. Any change that is due to change of health care provider, insurance company, etc, or is done for financial reasons, as long as in the same class of medication, will not be considered a violation of the inclusion criterion. Any change to prescription medication due to improvement of a disease outcome will not be considered a violation of the inclusion criterion.
• Women of childbearing potential (not surgically sterile or postmenopausal for greater than or equal to 1 year) must not be pregnant as indicated by a negative pregnancy test (urine or serum) within 24 hours prior to vaccine administration.
• Women of childbearing potential who are at risk of becoming pregnant must agree to practice adequate contraception (i.e., barrier methods, abstinence, monogamous relationship with vasectomized partner, intrauterine devices, Depo-Provera, Norplant, oral contraceptives, contraceptive patches or other licensed, effective methods) until 30 days following receipt of the last dose of vaccine.
• Able to understand and comply with planned study procedures.
• Able to provide informed consent prior to initiation of any study procedures and be available for all study visits.

Exclusion criteria

• Has occupational exposure to poultry, to include but is not limited to chicken, turkey, or duck farmer, factory worker in poultry processing plant, veterinary staff that handles poultry; has recreational exposure to poultry, e.g. raising poultry in 4-H club, duck hunter that slaughters/handles the "kill" or history of previous H5N1 vaccination or exposure.
• Has a known allergy to eggs, egg products or other components of the vaccine (including gelatin, formaldehyde, octoxinol, thimerosal and egg or chicken protein).
• Is female of child-bearing potential who is breastfeeding or intends to become pregnant during the study period up to 30 days following receipt of the last dose of vaccine.
• Has immunosuppression as a result of an underlying illness or treatment with immunosuppressive or cytotoxic drugs, or use of anticancer chemotherapy or radiation therapy within the preceding 36 months.
• Has an active neoplastic disease (excluding non-melanoma skin cancer or prostate cancer that is stable in the absence of therapy) or a history of any hematologic malignancy. Active neoplastic disease is defined as no neoplastic disease or treatment for neoplastic disease within the past 5 years.
• Has long-term use (greater than 2 weeks) of oral or parenteral steroids (glucocorticoids), or high-dose inhaled steroids (>800 mcg/day of beclomethasone dipropionate or equivalent) within the preceding 6 months (nasal and topical steroids are allowed).
• Has a history of receiving immunoglobulin or other blood products within the 3 months prior to enrollment in this study.
• Has received any other licensed vaccines within 2 weeks (for inactivated vaccines) or 4 weeks (for live vaccines) prior to enrollment in this study, or plans to receive any other licensed vaccines within 2 weeks (for inactivated vaccines) or 4 weeks (for live vaccines) following each study vaccine.
• Has an acute or chronic medical condition that would render vaccination unsafe or would interfere with the evaluation of responses. This includes, but is not limited to solicited reactogenicity symptoms, known chronic liver disease, significant renal disease, unstable or progressive neurological disorders, diabetes mellitus, and transplant recipients.
• Has a history of severe reactions following vaccination with contemporary influenza virus vaccines.
• Has an acute illness or has an oral temperature greater than 99.9 degrees Fahrenheit (37.7 degrees Celsius) within 3 days prior to enrollment.
• Has received an experimental agent (vaccine, drug, biologic, device, blood product, or medication) within 1 month prior to enrollment in this study, or expects to receive an experimental agent during the study period.
• Has any condition that would, in the opinion of the site principal investigator place the subject at an unacceptable risk of injury or render the subject unable to meet the requirements of the protocol.
• Has a diagnosis of schizophrenia, bipolar disease or other severe (disabling) chronic psychiatric diagnosis.
• Has been hospitalized for psychiatric illness, history of suicide attempt or confinement for danger to self or others.
• Is receiving psychiatric drugs. Subjects who are receiving a single antidepressant drug and are stable for at least 3 months prior to enrollment without decompensating are allowed enrollment into the study.
• Has known human immunodeficiency virus, hepatitis B, or hepatitis C infection.
• Has a history of alcohol or drug abuse in the 5 years prior to enrollment.
• Has a history of Guillain-Barré syndrome.
• Has any condition that the investigator believes may interfere with successful completion of the study.
• Plans to enroll in another clinical trial (that has a study intervention in the form of drug, biologic or device that could interfere with safety assessment of H5N1 vaccine) at any time during the study period.