The purpose of the study is to better understand how the use of antibiotics changes micro-organisms in the intestines. The change to micro-organisms in the intestines may change the body's vaccine immune response and alter the effectiveness of the IIV (seasonal flu) vaccine.

In particular, the investigators will be looking at certain markers in blood after vaccination with IIV (seasonal flu vaccine) with or without the use of antibiotics before vaccination.

There will be two randomized groups. Group A will start taking antibiotic by mouth 3 days prior to vaccination and continue taking antibiotics the day of vaccination and one day after vaccination for a total of 5 days. Group B will only receive the IIV (seasonal flu vaccine) and will not take any antibiotics.

The investigators hope to enroll 50 subjects at Emory.

We will study using a system biology approach the immune responses to IIV alone vs. IIV with antibiotic administration

Inclusion Criteria:

1. Healthy individuals aged 18-40 years.
2. Able to understand and give informed consent.
3. Women of child-bearing potential (not surgically sterile via tubal ligation, bilateral oophorectomy or hysterectomy or who are not postmenopausal for ≥1 year) must agree to practice adequate contraception that may include, but is not limited to, abstinence, monogamous relationship with vasectomized partner, barrier methods such as condoms, diaphragms, spermicides, intrauterine devices, and licensed hormonal methods for 30 days before and 30 days after TIV vaccination

Exclusion Criteria:

• You received blood product within 3 months of enrolling in the study or a live attenuated vaccine within 4 weeks or inactivated vaccines within 2 weeks.
• You received the 2014-2015 flu vaccine or had a confirmed case of influenza during 2014-2015.
• You received any antibiotics 6 months prior to enrolling in the study or expect to take antibiotics one month after vaccination.
• You received probiotics or prebiotics 3 months prior before enrolling in the study or expect to take one month after vaccination.
• You received proton pump inhibitors, H2 blocker receptors, or antacids 3 months regularly before enrolling in the study or one month after
• You had an allergic response or sensitivity to past vaccinations.
• You have health conditions that weaken your body's ability to fight infections or you are taking drugs like steroids that weaken your body's ability to fight infections.(Some nasal and topical steroids are allowed.).
• You have a chronic medical problem including (but not limited to) insulin dependent diabetes, severe heart disease including arrhythmias, severe lung disease, auto immune diseases and or grade 4 uncontrolled hypertension.
• Chronic neurological conditions such as seizure disorder, Parkinson disease, myasthenia gravis, neuropathy, or histories of encephalopathy, meningitis or ototoxicity.
• Any history of gastrointestinal disease, kidney or liver diseases.
• Alcohol or drug abuse or psychiatric conditions that in the opinion of the investigator would compromise your participation in this trial.
• Pregnant or are breast feeding.

365 days