The stability of cholera vaccine at elevated temperatures with regard to relative antigenicity

The oral cholera vaccine Shanchol™ when stored at elevated temperatures maintains the safety and immunogenicity profile in Bangladeshi participants

BACKGROUND

The oral cholera vaccine (OCV), Shanchol™ has shown protective efficacy lasting up to 5 years, however, requirement for a cold chain limits its use in resource poor settings. The study was conducted to determine the safety and immunogenicity of Shanchol in adult participants in Bangladesh when stored at elevated temperatures.

METHODS

The study was conducted in Mirpur, Dhaka. Four groups of healthy adult participants received two doses of Shanchol™, kept under standard storage temperature (Group A; 2-8°C) or at elevated temperatures (Group B, 25°C; Group C, 37°C; Group D, 42°C) for 14 days, respectively. Vaccine specific antibody responses were determined.

FINDINGS

145 participants were assigned to each group. Adverse events were mild not differing among groups. Vaccine stored at elevated temperatures remained stable with cumulative LPS content within admissible limits. Vibriocidal antibody responses were observed in all groups after each dose of vaccine at day 7 and 21 compared to pre-immune levels (P<0.001). Four-fold increases to Vibrio cholerae O1 Ogawa were observed at day 7 and/or day 21 after vaccination in the standard temperature and the three elevated temperature groups, with responder rates of; 76% (95% CI LB; 70%), 80% (95% CI LB; 74%), 69% (95% CI LB; 63%), and 74% (95% CI LB; 68%) in Groups A-D, respectively (P=0.240). Responses were also seen in all groups to V. cholerae O1 Inaba and V. cholerae O139 and in LPS specific IgA response to V. cholerae O1 antigens.

INTERPRETATION

This is the first report to show that the OCV is stable at elevated temperatures, and the safety and immunogenicity profiles are not altered. This information will help formulate global policies for use of the vaccine at higher temperatures, resulting in easier distribution and vaccination costs and decrease logistical challenges to vaccine delivery.

FUNDING

Bill & Melinda Gates Foundation.

TRIAL REGISTRATION

Clinical Trials.gov number NCT01762930.

Further observations on the stability of cholera vaccine at different temperatures

The stability of cholera vaccine samples held at 4-8 and 20-25 degrees C for 2 1/2 years was studied with regard to the number of organisms, total nitrogen content and relative antigenicity. After this length of time, the percentage loss in the number of organisms averaged 10.7 at 4-8 degrees C and 22.7 at 20-25 degrees C. The maximum loss in number of organisms took place during the first six months and in the next two years there was very little loss in the number of organisms. The total nitrogen content after 2 1/2 years remained almost unaltered at these temperatures. All the ten samples had acceptable relative antigenicity for both the Inaba and Ogawa serotypes after exposure at 4-8 degrees C for 2 1/2 years, while at 20-25 degrees C only two samples for the Inaba serotype and one sample for the Ogawa serotype retained antigenicity within acceptable limits after the same time. The loss of antigenicity after 2 1/2 years at 20-25 degrees C in comparison with antigenicity at 4-8 degrees C ranged from 41.5 to 83.1% (mean 61.9%) for the Inaba serotype and from 47.3 to 80.3% (mean 65.1%) for the Ogawa serotype. From this study on the cholera vaccine manufactured at the Central Research Institute, Kasauli, it is concluded that the shelf life of cholera vaccine may be increased from 18 months to at least 24 months, when the vaccine is stored under refrigeration.

Effects of elevated temperatures on the opacity and toxicity of pertussis vaccines manufactured with different inactivating agents

Plain pertussis vaccine manufactured with different inactivating agents was evaluated for its stability at 4-8, 25 and 35 degrees C with regard to the opacity and the toxicity [mouse weight gain test (MWGT) and histamine sensitizing (HS) activity]. Two pools each of heat inactivated pertussis vaccine (HIPV), formaldehyde inactivated pertussis vaccine (FIPV), glutaraldehyde inactivated pertussis vaccine (GIPV), thimerosal inactivated pertussis vaccine (TIPV) and acetone (I) treated pertussis vaccine [A(I)TPV] were taken for the study. The test for determination of opacity and MWGT were performed at monthly intervals for three months and the test for HS activity was performed after three months exposure of the samples at various temperatures. There was almost no loss in the opacity of GIPV and TIPV at all the selected storage temperatures and of HIPV and FIPV at 4-8 degrees C, while A(I)TPV lost about 16% opacity in three months at 4-8 degrees C. At 25 degrees C after three months, the percentage loss in opacity of HIPV averaged about 12, of FIPV 17 and of A(I)TPV 33. At 35 degrees C after three months, the average percentage loss in opacity of HIPV was 16, of FIPV was 25 and of A(I)TPV was 33. Regarding the effect of elevated temperatures on the toxicity of the vaccine, it was observed that the samples held at 35 degrees C for three months were the least toxic followed by those held at 25 and 4-8 degrees C as detected by MWGT and the test for HS activity.

Effect of storage temperatures on opacity and total nitrogen content of cholera vaccine

Fluid cholera vaccine was examined for its stability at 4-8 degrees C, 20-25 degrees C and 37 degrees C with regard to the number of organisms present and the total nitrogen content. Ten batches of fluid cholera vaccine manufactured at the Central Research Institute, Kasauli, India were taken for the study. The number of organisms was determined at weekly intervals for the first month and at monthly intervals for the next 11 months. The percentage loss in the number of organisms after one year averaged 6.5 at 4-8 degrees C, 20.6 at 20-25 degrees C and 21.5 at 37 degrees C. The maximum loss in number of organisms took place during the first six months at these temperatures, in the following six months the number of organisms remained almost constant even at 37 degrees C. The total nitrogen content of the vaccine remained virtually unaltered during the same period. From this study it was concluded that the number of organisms and the total nitrogen content does not reflect the antigenicity nor potency of the vaccine.