Letters to the Editor Indian Pediatrics 2005; 42:724-725 |
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Validity of the Shake Test to Identify the Frozen Damaged Vaccine Vials |
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During a training course at Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, the trainee doctors were asked to conduct the Shake test with a set of two vials - one unfrozen and one frozen as per the following steps given in modules(2). 1. Take two DPT/DT/TT/Hepatitis-B/Typhoid vaccine vials, one test vial and another from the same manufacturer (never frozen). 2. Shake both vials to mix sediments. 3. After 15 minutes, look at the vaccine inside the two vials. 4. If the vaccine is not uniformly mixed or the sediments/flocculation are still found settled at the bottom, the test vial was frozen at some or other time. Only 37% and 60% participants could correctly identify frozen and unfrozen vaccine vials respectively. This raises serious doubts about the validity and utility of the Shake test (as given in the module). In addition, the Shake test protocol is not correctly given in the module. Non-frozen sample cannot be used as a control vial. Besides this, the module does not mention about the comparison of the rate of sedimentation in the two vials that is the crux of the test (1). In fact, we located five versions of Shake test in the literature(1-4). Their steps are different. The WHO test uses a waiting period of 5-10 minutes while others quote 15, 30 minutes or even 24-72 hrs. Some use frozen vials as control whereas others use unfrozen ones. Some use ‘sediments/ floccules’ settled at the bottom of the vial as the evidence of previous freezing, whereas others, including WHO insist on rate of sedimentation in comparison to control vial. Thus, the steps of Shake test as described in the module were different from those described in the WHO modules. This issue needs to be discussed and settled to remove unnecessary confusion. Ashoo Grover,
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