Vaccines play a critical role in combating influenza and COVID-19, which are now endemic. Influenza vaccines have undergone significant advancements, including the introduction of split vaccines in the late 1960s, initiation of a national vaccination program for older persons in 2001, use of pandemic vaccines during the 2009 influenza pandemic, and, more recently, introduction of intranasal live-attenuated vaccines and high-dose inactivated vaccines. The COVID-19 mRNA vaccine was developed and mass vaccination implemented within a remarkably short period of one year following outbreak of the virus infection in late 2019.

In Japan, after seven campaigns of government supported vaccination campaigns starting in 2021, COVID-19 vaccination transitioned to a routine program in the autumn of 2024.

The efficacy of influenza vaccines is estimated at 40%-60%, which may not be sufficient. Similarly, while COVID-19 vaccines demonstrated high efficacy during the initial trials, their effectiveness declined over time and with the emergence of new variants. Most recently, a vaccine targeting the Omicron JN.1 variant has become available, but ongoing viral mutations highlight the need for continuous updation of this vaccine.

Systemic reactions to both vaccines are generally more frequent in younger individuals. For COVID-19 vaccines, multiple vaccinations have been reported in some studies to be associated with a reduction in the frequency and intensity of systemic reactions. Simultaneous administration of both vaccines may contribute to increasing the immunization coverage rate, and efforts are underway to develop combination vaccines to further streamline vaccination programs. To address the ongoing changes in the infectious disease environment, the Influenza Study Group of the Japan Physicians Association (JPA) has been conducting research on influenza vaccines and antiviral agents for over 20 years. We have now expanded our focus to include COVID-19. In this report, we present the findings on both vaccines from domestic and international studies, incorporating data from within the JPA.

Poor adherence to anti-influenza medications is sometimes observed and while differences in treatment adherence could affect the clinical efficacy, to date, there are no reported studies that have evaluated this aspect comprehensively. This observational study was conducted to investigate the relationship between adherence to the anti-influenza medication regimen and the number of days from the start of drug administration to resolution of influenza symptoms in pediatric patients aged 6 to 12 years with influenza. Results showed that the time to resolution of influenza symptoms was significantly shorter in the adherent group (1,305 patients) than in the non-adherent group (312 patients) (p<0.0001). This result suggested that adherence to the medication regimen was associated with earlier symptom alleviation.

Case. A 64-year-old woman who had undergone splenectomy at the age of 49 years was referred to our hospital with a history of fever and malaise; she had not received the pneumococcal vaccine. She was diagnosed as having septic shock and admitted to the hospital. On admission, fulminant purpuric patches were observed over her face, and the urinary test for pneumococcal antigen was positive. On Day 4, she was initiated on mechanical ventilation because of respiratory failure. Her blood pressure transiently increased to over 200mmHg and her consciousness level became progressively impaired. The fluid-attenuated inversion recovery (FLAIR) sequence on contrast-enhanced brain MRI showed extensive subcortical high-signal intensity areas and electroencephalography showed generalized epileptic discharges. Based on the above findings, the patient was diagnosed as having posterior reversible encephalopathy syndrome (PRES). Her consciousness improved with steroid pulse therapy and administration of anticonvulsants. She could be weaned from mechanical ventilation on Day 15 and was able to walk independently without sequelae. She was transferred to a rehabilitation hospital on Day 47. PRES should be considered in the differential diagnosis in patients with severe infections presenting with impaired consciousness.