About FILL Program



Following Infants with Low Lymphocytes

The United States Immunodeficiency Network (USIDNET), iIn collaboration with the Clinical Immunology Society (CIS) and The Jeffrey Modell Foundation (JMF), USIDNET has undertaken an effort to track what happens to infants who are identified at birth, or shortly after, as potentially having a primary immunodeficiency. The “Following Infants with Low Lymphocytes” program, “FILL” for short, allows us to collect important and specific medical information at three defined points in time (birth to 6 months, up to 1 year, 1 year to 18 months).


The FILL program’s online space allows for both patients and physicians to take action.



Patients Enrolled


Enrolling Sites


Patient States


Ways to Join


Patient Participation

For parents who would like to enroll their infants in the FILL project but do not have access to a USIDNET enrolling center, you can use this website to enroll your child through an IRB-approved online consent form. The USIDNET team will take care of the rest!

Click here if you are a parent


Enrollment Centers & Physicians

Physicians at active USIDNET enrolling centers can use their USIDNET username and password to access and enroll FILL patients. Additionally, there are other options for enrolling qualifying infants into the FILL program.

I want to login

I am not an affiliated physician