Inclusion Criteria:  Participants must meet all of the following criteria to be included in this study:  Non-smoking, male or female, age greater than or equal to (>=) 18 years and less than or equal to (<=) 65 years old at the time of informed consent. To be considered non-smokers, participants must have discontinued smoking for at least 4 weeks before dosing. Japanese participants (age >=20 years) must have been born in Japan of Japanese parents and Japanese grandparents, must have lived no more than 5 years outside of Japan, and must not have changed their lifestyle or habits, including diet, while living outside of Japan. Body Mass Index (BMI) >=18 and less than (<) 30 kilogram per square meter (kg/m^2) at screening.  Exclusion Criteria:  Participants who meet any of the following criteria will be excluded from this study:  Clinically significant illness that requires medical treatment within 8 weeks or a clinically significant infection that requires medical treatment within 4 weeks of dosing. Evidence of disease that may influence the outcome of the study within 4 weeks before dosing; example, psychiatric disorders and disorders of the gastrointestinal tract, liver, kidney, respiratory system, endocrine system, hematological system, neurological system, or cardiovascular system, or subjects who have a congenital abnormality in metabolism Exposure within the last 14 days before dosing to an individual with confirmed or probable corona virus disease-2019 (COVID-19) or symptoms within the last 14 days that are on the most recent Centers for Disease Control and Prevention list of COVID symptoms or any other reason to consider the participant at potential risk for COVID-19 infection Participants who had received COVID vaccine but are not 14 days post full vaccination before dosing Currently enrolled in another clinical study or used any investigational drug or device within 28 days or 5 half-lives of the other investigational drug, whichever is longer, preceding informed consent Prior exposure to lecanemab Hypersensitivity to lecanemab or any of the excipients, or to any monoclonal antibody treatment  NOTE-Other protocol defined Inclusion/Exclusion criteria may apply.