Study was terminated early . This decision was not due to any safety concerns associated with PF-07899895 but rather due to a business decision.

The purposes of the study are as follows:

• To understand how safe and tolerable are different amounts of study medicine (PF-07899895).
• To measure the amount of PF-07899895 in blood after the medicine is taken by mouth.

The study is seeking participants who:

• Are male or female of 18 to 65 years of age.
• Are in good health condition.
• Have not had viral infections (HIV, HBV, or HCV). HIV, human immunodeficiency virus. - HBV, human hepatitis B virus. HCV, human hepatitis C virus.
• Have tested negative for tuberculosis.

Participants will receive either PF-07899895 or placebo (dummy pill) by chance. In the first part of the study (Part A):

• each participant will receive a total of up to 5 doses of the medicine or placebo with at least 5 days between each dose.
• after each dose, participants will stay in study clinic for 3 to5 days.

In the second part of the study (Part B):

- each participant will need to take 10 days of dosing and will stay in the study clinic for clinical checks for 13 days.

In the third part of the study (Part C):

• In SD cohort, each participant will receive a total of up to 5 doses of the medicine or placebo with at least 7 days between each dose. After each dose, participants will stay in study clinic for 5 days.
• In MD cohorts, each participant will need to take 10 days of dosing and will stay in the study clinic for clinical checks for 13 days.

The planned duration of participation from screening to follow-up in:

• Part A of the study is up to 15 to 18 weeks.
• Part B of the study is up to 11 weeks.
• Part C of the study is up to 15 to 18 weeks. Participants will also have their blood collected by the study doctors for several times.

Inclusion Criteria:

• Participants, male or female, must be 18 to 65 years of age, inclusive, at the time of signing the ICD.
• BMI of 16 to 32 kg/m2; and a total body weight>50 kg (110 lb).
• Male and female participants who are overtly healthy as determined by medical evaluation including medical history, physical examination, vital signs assessments, oral temperature, 12-lead ECGs, and laboratory tests.

Exclusion Criteria:

• Evidence or history of clinically significant hematological, renal, endocrine, pulmonary, gastrointestinal, cardiovascular, hepatic, psychiatric, neurological, or allergic disease.
• Any condition possibly affecting drug absorption (eg, gastrectomy, cholecystectomy, bowel resection) or gastrointestinal (GI) transit time (eg, constipation).
• History of human immunodeficiency virus (HIV) infection, hepatitis B, or hepatitis C; positive testing for HIV, hepatitis B surface antibody (HBsAb), hepatitis B core antibody (HBcAb), hepatitis B surface antigen (HBsAg), or hepatitis C antibody (HCVAb); positive or indeterminate QuantiFERON test for tuberculosis. Hepatitis B vaccination is allowed.
• Any medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality or other conditions that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.
• History of undesired reactions to the sun (photosensitivity).
• Recent exposure to live or attenuated vaccines within 28 days of the screening visit.
• Use of prescription or nonprescription drugs and dietary and herbal supplements within 7 days or 5 half-lives (whichever is longer) prior to the first dose of study intervention, with the exception of moderate or strong cytochrome P450 3A (CYP3A) inducers or inhibitors which are prohibited within 14 days plus 5 half-lives prior to the first dose of study intervention.
• Previous administration with an investigational product (drug or vaccine) within 30 days (or as determined by the local requirement) or 5 half-lives preceding the first dose of PF-07899895 used in this study (whichever is longer). Participation in studies of other investigational products (drug or vaccine) at any time during their participation in this study.

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.