Changes in the occurrence of children’s asthma after the 2019 revision of the Health Promotion Act preventing passive smoking in Japan: interrupted time-series analyses

Abstract Aim Passive smoking contributes to serious health problems in children, including asthma and sudden infant death syndrome. In Japan, the Health Promotion Act was revised in February and July 2019, and regulations against passive smoking were strengthened to protect children. We evaluated the impact of the policy, which had remained unexamined. Methods We used the DeSC database in Japan. We included all children under the age of six years. Interrupted time-series analyses were conducted by fitting Prais–Winsten linear regression models to assess the association of the policy revisions with the outcomes, namely the monthly occurrence per 100,000 children of hospitalization or outpatient medication for severe asthma between May 2018 and March 2020. Results Neither the first revision in February 2019 nor the second in July 2019 was associated with a decrease in hospitalization for asthma or outpatient medication for severe asthma. The second policy was associated with a reduction in hospitalization for asthma among children whose parents had smoking habits. Conclusion Our findings show that the revised policies introduced in Japan did not decrease the occurrence of severe asthma in children. This can be attributed to a lack of awareness about the first policy among the public and only a marginal increase in compliance following the second revision among institutions serving vulnerable populations. This suggests that the Japanese government should implement measures to increase awareness of the policy and enforce strict repercussions for non-compliance.