|Non-mercury sensors and electronic recording devices were employed in a landmark evaluation of vaccine refrigeration equipment and storage practices. Above, Thermodynamic Metrology Group physicist Michal Chojnacky checks the readout on a small digital unit in a test refrigerator.|
The efficacy of stored vaccine is critically dependent on storage and handling practices, including the use of reliable temperature monitoring methods and properly controlled storage systems. The absense of those protections can result in substantial waste, diminished vaccine potency, and the need for revaccination.
NIST's Thermodynamic Metrology Group evaluated the Centers for Disease Control and Prevention (CDC) cold-chain management systems and methods for the Vaccines for Children Program (VFC) under conditions that replicate typical practices of vaccine providers.
The NIST scientists systematically uncovered key factors causing widespread problems. They identified suitable commercial refrigerators for vaccine storage; evaluated the impact of operating conditions on refrigerator performance; determined proper placement of thermometers to monitor temperature; utilized continuous temperature data collection to detect previously unrecognized thermal excursions; and developed improved cold-chain management practices.
The project began in 2009 when CDC officials approached NIST to investigate storage and temperature monitoring issues that were causing significant losses from discarded and potentially ineffective VFC vaccines -- a program that distributes approximately $4 billion worth of vaccines annually to low-income families via more than 44,000 VFC providers.
Refrigerator temperature control, proper storage methods, and effective continuous temperature monitoring systems are critical to maintaining vaccine potency. Temperature excursions outside the normal range of 2 °C to 8 °C render many vaccines ineffective. A meta-analysis published in the journal Vaccine, including studies published in more than 20 countries, estimated that 14% to 35% of vaccines are subjected to accidental freezing – the largest source of vaccine loss. Additional, undocumented temperature excursions may also occur, creating the potential for ineffective vaccines to be unknowingly passed on to patients.
Future activities in the NIST project include: evaluating different types of freezer systems used to store vaccines at temperatures below –15 °C; examining the kinetic temperature of vaccine fluid (contained in vials and syringes) to determine the optimal amount of glycol or other non-toxic buffer medium needed to mimic vaccine fluid temperature; and characterizing the different types of digital thermometers needed for vaccine cold chain management.
The documents, presentations, and tutorials developed for the CDC VFC program and listed at right provide a basic understanding of proper cold chain management designed to reduce vaccine waste and prevent ineffective inoculations.