POST 00406E : FREEZING AND VACCINE EFFICACY

POST 00406E : FREEZING AND VACCINE EFFICACY How much does freezing affect vaccine efficacy? 4 January 2002 ________________________________________________ The question of the effect of freezing of efficacy of vaccines has been raised in previous postings. James Cheyne has been looking at this question again. A review of five references over 20 years shows, so far, that the story is not yet complete. These references are the WER (1980), the WHO Bulletin (1997), WHO (Thermostability of vaccines 1998), Plotkin and Orenstein :"Vaccines", third edition (1999) and "Vaccine" (May 2001). After this brief review, James concludes by asking three relevant alternative questions. _________________________________________________ * The WER (1980) says that "Three [adsorbed and unadsorbed DPT] vaccines suffered losses of pertussis component potency after being frozen. other vaccines were tested for pertussis potency, with no significant changes being recorded. One of them showed physical changes after freezing; one did not" * The WHO Bulletin (1997) says that six out of seven samples of the tetanus component of DTP showed "no significant differences between potency of vaccine stored at +4 degrees after freezing to -5 degrees, -10 degrees, and -20 degrees. But after freezing to -30 degrees three out of seven samples showed a decreases in potency of 29% to 55%". * WHO (Thermostability of vaccines 1998) says "Freezing can reduce the potency of tetanus toxoid to an extent that evidently varies slightly with the composition of the vaccine. The tetanus toxoid component in five DPT vaccines stored for 12 hours at -30 degrees showed decrease in potency of about 30%, while there was no such decrease in vaccines kept between -5 degrees and -10 degrees. However, the potency of the tetanus toxoid component of adsorbed DT vaccine was reduced after freezing at both -5 degrees and -30 degrees. This difference is undoubtedly due to the adjuvant effect of the pertussis component in the DPT vaccine when the potency is tested by animal assay. The relevance of this observation to protective efficacy is not known. "Frozen monovalent tetanus toxoid , especially that frozen four times, stimulated a lower mean response and lower proportion of high titres than the unfrozen product in young military recruits, although the significance of the difference was unclear. All persons immunized with frozen toxoids, however, acquired protective levels of tetanus antitoxin. Freezing did not seem to affect the immunogenicity of unadsorbed toxoid (which remained less immunogenic than the adsorbed product)". The text continues; "...as with other vaccines adsorbed on aluminium salts, freezing HB vaccine MAY cause a significant loss of potency..." (My emphasis - JC) * Plotkin (1999) says that DTaP, DTwP and DTP-Hb "... stored at ) -----------------------------------------------------------------------------