Evaluation of potency of measles vaccine used in Iran: comparison of WHO and NIBSC method in cell culture

Measles has been a major cause of illness and death in children and vaccination against the disease is part of the WHO global immunization program. A suitable vaccine should create maximum immune response against the pathogen and must be safe for the user. Thus, after production, vaccines must be analyzed and controlled by the producer and confirm by relevant governmental organizations. The Food and Drug Control Lab (FDCL), Ministry of Health, is the secondary control center on potency of vaccines in Iran. In this study, we have set up the WHO and NIBSC methods in FDCL and compare these methods on determining the potency of measles vaccine.

Measles vaccines were obtained from Razi Institute Iran. Nine dilutions of vaccine (10^-1 to 10^-5) in 0.5 log interval were mixed with Vero cell suspension and seeded. In WHO method, the cells were incubated at 36°C for 10 days, during which the cells were checked for cytopatic changes everyday. To set up the assay, we tested the vaccine dilution with four different cell suspensions (2×10⁵-5×10⁴/well) and four different concentration of serum (2.5-10%). Based on our results, in the assays, 5% serum and 1×10⁵ cells were used. The potency assay was performed with six different vaccines produced in one batch and the mean potency for Measles was 10^{4.32 ± 0.24} CCID₅₀/vial for a ten-dose vial. In NIBSC method following seeding of Vero cells, the medium was removed after 3 hours and overlay was added. Then the plates were incubated at 35°C for 10 days. After incubation period, the overlay was removed, the plaques were stained with methyl violet and counted. This assay was repeated three times and the mean of the results was 5.83 ± 0.03 log₁₀ PFU/dose.

In this study, we have set up the WHO and NIBSC methods and results indicated that the potency of the vaccine is in acceptable range in either method. Furthermore, the WHO method is simple and less time consuming compared to NIBSC which is complicated and requires more effort to produce reproducible results.