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The article reports on the introduction of inactivated poliovirus vaccine (IPV) and its impact on the risk for vaccine-associated paralytic poliomyelitis (VAPP) in Beijing, China, from 2014 to 2016. The government introduced IPV into the city's Expanded Program on Immunization (EPI) in December 2014. Acute flaccid paralysis surveillance was used to identify VAPP cases in the city during the period.

In the absence of photochemical reactions, nocturnal ozone (O 3) variation was found to be caused by boundary layer meteorological processes. In addition to low-level jet (LLJ) and convective storm (CS) events, cold front and foehn processes also cause nocturnal O 3 increases (NOIs). The subsidence warming effect (Subsi.) caused by weak cold front and foehn processes cause the nocturnal surface temperature and O 3 to increase. Statistical analysis revealed that NOI days accounted for 39.4 ± 6.4% of the total number of days per year in Beijing, and the average occurrence frequency decreased by 1.7%/year over a recent five-year period (2018–2022). The LLJ process is the primary factor causing NOIs, and the average annual contributions of the LLJ, CS and Subsi. processes to NOIs were approximately 32.2 ± 10.5%, 11.7 ± 2.3% and 8.0 ± 3.0%, respectively. From a seasonal point of view, the most NOI events occurred in summer, and the least occurred in autumn. LLJs contributed the most to the NOIs in each season, and the CS contribution was almost equal to that of LLJs in summer. LLJs that occurred near 00:00 LT and 04:00 LT had a greater probability of causing NOI events. Most of the nocturnal CS events occurred during 22:00 LT-02:00 LT (next day), and the contribution of CSs to NOIs fluctuated around 10.0%. More than half (68.0%) of the Subsi. events occurred during 23:00 LT-03:00 LT (next day). Subsi. events occurred during this period contributed more to NOIs than other periods. Meteorological processes more easily caused NOI events in the urban, Daxing and Tongzhou districts than other areas. The average surface O 3 concentration during the early morning hours (04:00–06:00 LT) on NOI days was 8.8 ± 3.2 μg/m3 higher than that on non-NOI days, suggesting that NOIs can elevate the base O 3 concentration during the following day. • Except for the LLJs and CSs, the weak cold front and foehn are also triggers for NOI events. • LLJ is the primary factor causing NOIs, followed by the CSs. • Contributions of the LLJ, CS and Subsi. processes to NOIs increased consistently with their occurrence frequency before midnight. [ABSTRACT FROM AUTHOR]