MASS SCREENING AND VACCINATION STRATEGIES: CASE OF CERVICAL CANCER IN JAPAN

Purpose: The purpose of this research is to investigate the best preventive strategy against cervical cancer when mass screening and vaccination are simultaneously considered.

Method(s): A mathematical model of age structured population under the risks of the infection of HPV (Human papillomavirus) and cervical cancer was constructed where the infection of HPV through sexual contact and the progression of cervical cancer from the infection of HPV took place. Required medical cost and mortality were taken into account. In the analysis of cost and benefit, the expense of mass screening and vaccination in addition to the loss due to mortality induced by cervical cancer were involved. Vaccination is assumed to be offered to young female of age 10-14. Vaccination is only effective for HPV 16/18 and parameters are calibrated so that 70% of cervical cancer caused by high risk HPVs was prevented. Parameters were set as close as the contemporary situation of Japan. ICER (incremental cost-effectiveness ratio) was calculated to investigate the efficiency of possible strategies. ICER less than approximately 4 million yen/QALY was considered efficient.

Result(s): Cost benefit analysis was carried out according to different levels of vaccination rates and mass screening participation rates. As to the effect of the vaccination rate, total medical cost was decreased as vaccination rates increased. At the same time, ICER was kept low and decreased as vaccination rate increased (350 - 295 thousand yen as vaccination rate 20 – 100%). Under the condition that the vaccination rate of cancer screening is 100%, mass screening is not economically acceptable if the participation rate exceeded 40%. This implies that the cost required for mass screening is not efficient.

Conclusion(s): The prevention of cervical cancer by the vaccination against HPV were effective except for the cases of the execution of mass screening with very high participation rate. This was considered due to mass screening with plentiful cost without successful performance. Recently the serious side effect was reported as to the vaccination against HPV and the vaccination program has not been recommended in Japan. The analysis involving such harmful effect is also discussed.