The rate in reduction of potency increases as vaccines are exposed to higher temperatures. In order to maintain quality, vaccines must be continuously stored at their appropriate temperatures. Once potency is lost, it cannot be restored, and vaccine no longer provides any protection against the target disease.
Some vaccines are very sensitive to strong light and their exposure to ultraviolet light causes loss of potency. BCG and Measles vaccines are equally sensitive to light as well as to heat. In order not to be damaged in a short time, biological substances including vaccines and antisera should be protected from sunlight exposure.
The influence of humidity can be avoided if the vaccines packed well (hermetically sealed containers), and not stored open.
THE PACKAGING METHOD DURING SHIPPING
Generally, vaccine and antisera should be dispatched under cold condition. During shipment, product should be well-packages in order to maintain a good temperature. During transportation, avoid direct sunlight.
Even when stored at the proper temperature, vaccines do not retain their potency indefinitely. Every vaccine has an expiry date. This is the date by which the vaccine must be used. It is printed on all labels during manufacture and is valid only if the vaccine is properly stored and transported at all times in accordance to the requirements. If the vaccine is damaged by heat or others causes, its potency will be reduced before the expiry date shown on the labels.
THE USE OF THE OPENED MULTI-DOSE VIALS IN SUBSEQUENT IMMUNIZATION SESSION
The safety of vaccine in multi-dose vial is primarily dependent on risk of contamination by a pathogenic organism and bacteriostatic or virucidal effect of preservatives in the vial. The risk of contamination is higher in multi-dose vial than in a single-dose vial because the vaccine is repeatedly exposed-every time a dose is withdrawn. Most freezedried (lyophilized vaccines) do not contain preservatives and consequently must not be kept more than the manufacturer’s recommended limit.