The alum-adsorbed vaccines such as DPT, DT and TT must never be frozen, as this irreversibly alters them and markedly reduces their immunogenicity. When an alum-based vaccine is frozen, the lattice gets broken, and the alum content tends to agglomerate and gets heavier and sediments faster. This faster rate of sedimentation forms the basis of positive Shake test, which attempts to compare the flake formation and rate of sedimentation in the ‘test’ and ‘control’ vials of same manufacturer(1). If the control vial (known to be previously frozen) shows much faster sedimentation than in the vial being tested, the vaccine in question is probably potent and may be used. If, however, the sedimentation rate is similar and the test vial contains flakes, it should not be used.

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).

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,
Amarjeet Singh,
Department of Community Medicine,
Post Graduate Institute of Medical
Education and Research,
Chandigarh 160 012, India.
E-mail: [email protected]   

1. WHO Safe Vaccine Handling, cold chain and immunization; Module 3, EPI modules, Vaccine division, World Health Organization. WHO/EPI/LHIS/98.02

2. Anonymous. Maintenance of Cold Chain, Module 3, Immunization Strengthening Project, National Institute of Health and Family Welfare, Government of India 2002.

3. The expanded progamme on immunization in South Africa. Available from URL: http://www.hst.org.za/pubs/edl/phc/10.6asp-9k

4. VSO: Pharmacy procedures by Rachel Blake. Available from URL: http://www.oneworld. org/vso/pubs/wpapers/pharm/6.htm