A Study to Evaluate AAV9 Neutralizing Antibody Seroconversion in Household Contacts.

This single center study to include approximately 50 to 250 participants is designed to estimate the likelihood of NAb seroconversion to AAV9 because of exposure to shed viral vector material released by a DMD participant treated with PF-06939926 in study C3391003. Eligible participants will undergo a blood draw provided by a Home Health Care Vendor at three home visits.

To maintain the blinded nature of study C3391003, all C3391007 study participants and investigators as well as the sponsor will remain blinded to the Cohort assignment of the C3391003 study participant in the same household until C3391003 becomes unblinded. Additionally, the detailed individual results will be considered sensitive clinical data and will not be shared with the participants, investigators, or the Sponsor until study C3391003 becomes unblinded.

The total duration of participation in the study is up to 4 months, including up to 48 days for the screening/baseline period and up to 66 days after dosing of investigational product in the C3391003 participant of the same household.

Inclusion Criteria:

1. Males or females who weigh at least 9 kg
2. Anticipated to be living or working in the same household (> or = 10 hours per week and expected to have direct contact with the participant) as a participant in the Phase 3 interventional study, C3391003, for at least 4 months from the time of the screening visit. The participant in C3391003 must have completed their Baseline Visit, but not yet have received IP as part of C3391003
3. The C3391003 participant is subsequently dosed with study intervention after the Baseline Visit

Exclusion Criteria:

1. Prior treatment with gene therapy utilizing AAV vectors of any serotype.
2. Living or working in a household where 5 other participants are already participating in this study (C3391007).