Extending supply chains and improving immunization coverage and equity through controlled temperature chain use of vaccines
One way to strengthen immunization supply chains is to expand the use of vaccines in a controlled temperature chain (CTC). A method for increasing vaccine access and coverage, especially among hard-to-reach populations, CTC permits certain vaccines used in single antigen delivery strategies or campaign scenarios to be kept outside of the traditional cold chain of +2 °C to +8 °C for a short period of time under monitored and controlled conditions that are appropriate to the stability of the antigen. A CTC typically involves a single excursion of the vaccine into ambient temperatures not exceeding +40 °C for the duration of a specific number of days just prior to vaccine administration Dedicated training and supervision is an integral part of the CTC approach, ensuring health workers are not subject to confusion between vaccines eligible for removal from the cold chain and those not. CTC use of vaccines is currently limited to campaigns and special strategies; where vaccines are administered in isolation of other EPI vaccines. The CTC approach also uses two specific and complementary temperature monitoring tools: (1) a peak threshold temperature indicator which allows for brief- though all the same harmful- exposures to high temperatures to be detected and (2) the VVM which measures accumulated heat exposures during unintentional cold chain excursions and is limited to a calibration for an upper temperature limit of +37 °C. CTC therefore not only formally allows for cold chain excursions through the regulatory approval process, but also extends their flexibility and improves the associated temperature monitoring. A growing and compelling body of evidence shows CTC offers valuable opportunities for maximizing supply chain efficiencies, safeguarding cold chain investments, and protecting more children and families from vaccine-preventable diseases.