What Is a Vaccine Titer?

A vaccine titer (also called a serologic test or immunity test) is a blood test that measures the level of antibodies in your blood against a specific disease. Antibodies are proteins produced by your immune system in response to vaccination or prior infection. A positive titer result — meaning your antibody levels exceed a defined threshold — demonstrates that you have immunity to that disease, even if you cannot produce vaccination records.

Which Vaccines Have Accepted Titer Alternatives?

Under USCIS requirements, titer testing is accepted as evidence of immunity for several vaccines, including:

• Measles — IgG antibody titer
• Mumps — IgG antibody titer
• Rubella — IgG antibody titer
• Varicella (chickenpox) — IgG antibody titer
• Hepatitis B — hepatitis B surface antibody (anti-HBs) titer

Vaccines Without Accepted Titer Alternatives

Not all vaccines have accepted titer alternatives under USCIS requirements. For vaccines such as influenza, Tdap, pneumococcal, meningococcal, COVID-19, and HPV, titer testing is generally not accepted as a substitute for vaccination. For these vaccines, you must either provide documentation of prior vaccination or receive the vaccine.

The Titer Testing Process

Titer testing involves a simple blood draw. The blood sample is sent to a laboratory, and results are typically available within a few days to a week. If your titer results demonstrate adequate immunity, the civil surgeon will document this on Form I-693 and the vaccination requirement for that disease is satisfied.

If your titer results are negative or equivocal — meaning your antibody levels are below the threshold for demonstrated immunity — you will need to receive the vaccine. A negative titer does not necessarily mean a prior vaccine failed; immunity can wane over time.

Cost and Practical Considerations

Titer testing adds cost and time to the immigration medical examination process. Whether titer testing makes sense for you depends on the specific vaccines in question, your medical history, and practical factors such as cost and scheduling. For some applicants, simply receiving the missing vaccines is faster and less expensive than titer testing. Our civil surgeon will help you evaluate the best approach for your situation.