Using desk location information and employees' building entry/exit swipe card data from a company that offered a free 2-day worksite influenza vaccination clinic, we separately identify the vaccination effects of base proximity-the inverse of walking distance between one's desk and the clinic-and functional proximity-the likelihood of passing near the clinic during the course of a normal work day (ie, days when the clinic is not open).

We study the 2011 influenza vaccine uptake of employees at the headquarters of a health benefits administrator in the United States. These employees are generally not health care personnel. All of them have health insurance. Of the company's total workforce (including those not based at the headquarters), 26% are African Americans and 37% are racial minorities.

There are 2 main buildings at the company headquarters. Building One houses 520 employees and is the site of the vaccination clinic; Building Two houses 1281 employees. The 2 buildings are 131 meters apart and connected by an enclosed passageway. The clinic was located near the cafeteria in Building One and adjacent to the passageway connecting the 2 buildings. The clinic was conducted from October 19 to 20, 2011, and it was advertised during the 3 weeks prior.

The company requires employees to swipe a personalized electronic badge to open the external doors of its buildings, which include the doors to the passageway between the buildings. The company provided us data on the date and time of each swipe in September and October 2011. If an employee swipes her badge and holds the door open for another employee, we do not observe that other employee. The badge swipe data are therefore an incomplete measure of all movements between the buildings. The company also gave us data on employee characteristics and vaccination uptake, scaled architectural plans of the buildings, and employee desk maps.

Inclusion Criteria:

• Employee of Express Scripts.
• Eligible to receive a flu shot at Express Scripts.
• Over 18 years of age.

Exclusion Criteria:

• Children
• Non Express Scripts employees

Employees at the headquarters of a health benefits administrator in the US. These employees are generally not health care personnel. All of them have health insurance.

Of HQ employees, 520 are housed in Building 1 (the site of the vaccination clinic) and 1,281 are housed in Building 2. The two buildings are 131 meters apart and connected by an enclosed passageway. The clinic was located near the cafeteria in Building 1 and adjacent to the passageway connecting the two buildings.