Description of Maxi-Vac Programs


The World Health Organization formally declared the eradication of smallpox on May 8, 1980. Following this major public health accomplishment, smallpox vaccinations were ceased throughout the world. As a result of the cessation of vaccination, millions of Americans and people around the world have no immunity to the smallpox virus. Although the last recorded natural case of smallpox occurred in 1977, the intentional release of the smallpox virus has emerged as a potentially devastating bioterrorism threat. Given the vulnerability of the world population to smallpox, such an attack could have devastating consequences.

To help states and local communities prepare to respond to a smallpox attack should one occur, the Centers for Disease Control and Prevention of the U.S. Department of Health and Human Services has released generic guidelines on how to set-up a smallpox vaccination clinic. However, individual states and communities have differing numbers of qualified personnel that would be available in such an event.

Overview of Maxi-Vac Programs

Download Maxi-Vac Version 1.0 and Maxi-Vac Alternative

Maxi-Vac programs (both Version 1.0 and Alternative Version) help a public health official answer the following question: “How can I allocate the limited number of personnel available so that the maximum number of people are vaccinated in a 24 hour period?”

Maxi-Vac was developed by first building a computer model using both Arena® simulation software (version 5.0, Rockwell Software, Inc. Sewickley, PA) and an add-on optimization program (OptQuest®, version 5.0, OptTek Systems, Inc., Boulder, CO). The objective of the mathematical model was to allocate personnel such that a maximum number of people could be vaccinated in a clinic during a 24 hour-period. Built into the model was the stipulation that the average time spent in the clinic by the patients was less than or equal to 90 minutes. The data generated by each run of the model is stored in Maxi-Vac’s database. Based on your inputs (e.g., the number of personnel available for each shift in a clinic), the appropriate set of data is accessed in the database and displayed in the “Results” section of Maxi-Vac. Technical details on the underlying assumptions used in Maxi-Vac are provided in the Appendix of this manual.

Description of the Simulation Model

A smallpox vaccination clinic consists of a number of “stations,” or activities, that a patient may “visit.” The actual number of stations that a given patient “visits” will depend upon that patient’s personal circumstance (e.g., history of a possible pre-existing medical condition indicating that they should not be vaccinated unless exposed to somebody who was infectious) and the actual requirements for giving smallpox vaccinations. Clinic personnel must of course, staff each station. The stations, or activities, are:

  • Triage: Before patients enter the clinic they go through a triage point where they are triaged by a medical provider for illness and/or to determine whether they have been in contact with confirmed cases of smallpox. This checkpoint is to screen out those individuals that may be ill or who may be contacts from the rest of the individuals at the clinic so as not to expose the clinic population. Examples of persons who will not be treated in the clinic after being triaged are those that are ill and therefore require treatment at another site, and those that are identified as contacts.
  • Orientation: Individuals will view a video that contain a variety of information, such as care of the vaccination site, possible side-effects, when and how to seek treatment for such side effects, and (where necessary) the essential elements of informed consent as promulgated in 21 CFR 50.25.
  • Medical Forms: All individuals (contacts and mainstream) will receive an information packet that will include medical screening and consent forms (where necessary) to be filled out for each family member.
  • Referral: The completed medical screening forms mentioned above will be reviewed by non-medical personnel to see if the patients have self-reported any history of a possible pre-existing medical condition indicating that they should not be vaccinated unless exposed to somebody who was infectious (contraindications). Patients with potential contraindications will then proceed to the medical screening area; all others go directly to the vaccination area.
  • Medical Screening: Patients who self-reported contraindicating conditions on their screening forms will receive screening and information from a medical professional. If the person conducting the screening is uncertain, or the patient wishes more information, that patient will be referred for additional screening to a qualified physician.
  • Physician Evaluation: Patients with self-reported contraindicating conditions receive a more detailed screening if deemed necessary by the medical screener.
  • Vaccination/Witness: Patients receive their smallpox vaccinations from an approved medical provider. A second medical provider acts as witness. To limit fatigue, the medical providers can, during the course of their shift, switch occupations.
  • Exit Review: This is the final station in the clinic. Patients can have any remaining questions answered, and the personnel staffing this station can ensure that each patient exits with their information sheets and instructions.

Modeling Philosophy: Sensitivity Analyses and Overall Objectives

Much of the input data required for the model is unknown. The values used in the model are therefore mostly based on expert opinion. Even those data may not be reliable predictors of the process times and staff that will be required to engage in large-scale mass smallpox vaccinations. Therefore, we encourage you to be realistic when interpreting the results obtained from this software.

Given this uncertainty, we also encourage you to run the model several times. Once you have become adept at using the software, you may wish to consider a plan wherein you systematically alter the values of input variables. You may alter one variable at a time (univariate sensitivity analysis), or alter the values of two or more variables simultaneously (multivariate sensitivity analysis). Different results due to using different values for the various input variables will help you obtain a sense of the relative importance of each staff type in determining the number of people that can be treated in a 24-hour period. We have included in the results the impact of adding or removing one of each type of staff, which again, will give you a sense of the relative importance of increasing or decreasing staff at a specific station.


Washington ML, Mason J, Meltzer MI. (2005). Maxi-Vac: A tool to assist in planning mass smallpox vaccination clinicsExternal. Source: Journal of Public Health Management and Practice. 11(6):542-547.


Please keep in mind that this is a test version of the software and a draft version of the manual. The numbers generated through use of the software should not be considered predictions of what will definitely occur whilst running a mass immunization clinic. Rather, they are estimates of what could happen. The findings and conclusions of this manual and software are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.

Help and Feedback

For help using Maxi-Vac and/or interpreting the results, please e-mail your questions to Dr. Martin Meltzer. Please note that we are not commercial developers of software, and we ask for your patience if it takes us some time to reply to your requests.