The aim of this study was to collect further information regarding an increase immune response of SP284 after an additional dose in Japanese participants.

Primary Objective:

• To evaluate and describe the immune responses to meningococcal antigens (serogroups A,C, Y and W-135) at 28 days following each vaccination with SP284 vaccine in participants 20 through 55 years of age.

Other Pre-specified objective:

• To describe the safety in terms of immediate systemic adverse events (AEs), solicited reactions, unsolicited non-serious adverse events, and serious adverse events (SAEs) following receipt of each dose of SP284 vaccine in persons 20 through 55 years of age.

All participants received a 2-dose series of the study vaccine with 8-week interval and was monitored for safety and assessed for immunogenicity at baseline (pre-vaccination) and at 28 to 35 days following each vaccination.

Inclusion Criteria:

• Aged 20 through 55 years on the day of inclusion,
• Informed consent form had been signed and dated by the participant,
• Able to attend all scheduled visits and to comply with all trial procedures,
• For female participants who had childbearing potential, use of an effective method of contraception from at least 4 weeks prior to vaccination until at least 4 weeks after vaccination
• a) "20 through 55 years" meant from the day of the 20th birthday to the day before the 56th birthday.
• b) To be considered to be not of childbearing potential, a woman must either had undergone surgical sterilization (hysterectomy or bilateral tubal ligation) or be postmenopausal (at least one year without menses) at the time of vaccination. Effective methods of contraception include oral contraception (pill), intrauterine device, diaphragm or condoms used with sponge, contraceptive foam or cream, hormonal implants, transdermal patch, or parenteral contraception.

Exclusion Criteria:

• Chronic illness that, in the opinion of the investigator, was at a stage where it might interfere with trial conduct or completion,
• History of meningococcal diseases, confirmed either clinically, serologically, or microbiologically,
• Known systemic hypersensitivity to any of the vaccine components, or history of a life threatening reaction to a vaccine containing the same substances of the study vaccine,
• Known or suspected congenital or current/ previous acquired immunodeficiency; or receipt of immunosuppressive therapy such as anti-cancer chemotherapy or radiation therapy within the preceding 6 months; or long-term systemic corticosteroids therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3 months),
• Participation in another clinical trial investigating a vaccine, drug, medical device, or medical procedure in the 4 weeks preceding the trial inclusion,
• Planned participation in another clinical trial during the present trial period,
• Receipt of immune globulins, blood or blood-derived products in the past 3 months, which might interfere with assessment of the immune response,
• Receipt of any vaccine within the four weeks preceding the trial vaccination, except for influenza vaccination, which might be received at least two weeks before the study vaccine,
• Planned receipt of any vaccine during the trial period,
• Clinical or known serological evidence of systemic illness including Hepatitis B, Hepatitis C and/or Human Immunodeficiency Virus infection,
• Participant was pregnant, or lactating, or of childbearing potential (to be considered of non-childbearing potential, a female must be pre-menarche or post-menopausal for at least 1 year, surgically sterile, or using an effective method of contraception or abstinence from at least 4 weeks prior to the first vaccination and until at least 4 weeks after the last vaccination),
• Known thrombocytopenia, contraindicating intramuscular (IM) vaccination,
• Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating IM vaccination,
• Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily,
• Current alcohol abuse or drug addiction,
• Identified as employee of the Investigator or study center, with direct involvement in the proposed study or other studies under the direction of that Investigator or study center, as well as family member (i.e., immediate, husband, wife and their children, adopted or natural) of the employees or the Investigator,
• Previous vaccination against meningococcal disease with either the trial vaccine or another vaccine,
• At high risk for meningococcal infection during the trial,
• Febrile illness (temperature ≥ 37.5°C) or moderate or severe acute illness/infection (according to investigator judgment) on the day of vaccination. A prospective participant should not be included in the study until the condition had resolved or the febrile event had subsided,
• Received oral or injected antibiotic therapy within the 72 hours prior to blood draw (Visit 1),
• History of Guillain-Barré Syndrome (GBS).