A worker labels a box containing vaccines against tetanus and meningitis before stacking it with others on a truck at the EPI center. Advisories on the box warn that the contents are perishable and temperature sensitive. To keep their potency, the vaccines must be kept at a constant low temperature. A worker labels a box containing vaccines against tetanus and meningitis before stacking it with others on a truck at the EPI center. Advisories on the box warn that the contents are perishable and temperature sensitive. To keep their potency, the vaccines must be kept at a constant low temperature.