Timing of Flu Vaccine in HIV Patients May Affect Incidence Later in Season

PHILADELPHIA, PA—Early season influenza vaccination of patients with HIV may influence the risk of infection later in the season, reported Elizabeth R. Glinka, PharmD, BCPS, and Scott T. Johns, PharmD, BCPS, from the Veterans Affairs San Diego Healthcare System, San Diego, CA at IDWeek 2014. 

Peak months of flu activity are recorded annually by the Centers for Disease Control and Prevention (CDC), and in the U.S., influenza tends to have two peaks. The first is in late November, followed by an often larger peak between January and March. Peak antibody titers develop 2–4 weeks after influenza vaccination, but once immunity is acquired it begins to wane over time. Patients with HIV are at risk for a rapid decline in protective immunity, making them more susceptible to influenza infection.

“Antibody titers wane over time,” reported Dr. Glinka, “but it is unclear if timing of influenza vaccination within the flu season affects the probability of an influenza infection later during the flu season.” 

To address this, Dr. Glinka and Dr. Johns conducted a retrospective cohort study on the relationship between the occurrence of flu or influenza-like illness in HIV patients and the time after influenza vaccine was administered. Patients were included if they had laboratory confirmed influenza, influenza diagnosed by a physician, or retrospectively met criteria for influenza-like illness. Specific criteria for influenza-like illness included: fever (temperature >100°F) and cough/upper respiratory symptoms.

Patients were identified by retrospective chart review at the VA San Diego Healthcare Systems, from Sept 2005 to May 2013. Patients were considered as vaccinated early if had been vaccinated between September 1st and November 15th (n=2773), or late if vaccinated after November 15th (n=1802).

Of the 37 vaccinated HIV patients who developed influenza, the majority were vaccinated early (n=30) compared to late (n=7), and 100% were male. There were no significant differences between viral load or CD4 count between the two groups.

There was a higher incidence of flu in patients vaccinated early (1.1%, 30/2773) compared to late (0.4%, 7/1802) P=0.0105. Furthermore, patients vaccinated early were more likely to develop flu later in the season. A total of 70% (26/37) of vaccinated patients developed flu after January 15th.