Reliability of direct varicella zoster virus loop-mediated isothermal amplification method for rapid diagnosis of breakthrough varicella

Analysis of the reliability of rapid diagnostic tests for varicella, including breakthrough cases

In the era of universal varicella vaccination, diagnosis of varicella is challenging, especially for breakthrough cases. We sought to clarify the reliability of direct varicella-zoster virus (VZV) loop-mediated isothermal amplification (LAMP) and DermaQuick® VZV using the immunochromatography technique as rapid diagnostic tests for varicella. In addition, the usefulness of saliva as a sample type for direct LAMP was investigated. Among the 46 enrolled patients with suspected VZV infection, 31 patients (67.3%) were positive for the nucleic acid test based on real-time PCR from skin swab samples. Direct LAMP of skin swabs was positive in 29 (63.0%) of 46 patients. DermaQuick® VZV was positive in 25 (54.3%) of 46 patients. VZV DNA was detected in only 48.4% of oral swabs with the direct LAMP method. With real-time polymerase chain reaction (PCR) as the standard for diagnosing varicella, the sensitivity and specificity of DermaQuick® VZV were 80.7% and 100%, respectively. The sensitivity and specificity of direct LAMP from skin swabs were 93.6% and 100%, respectively. The sensitivity and specificity of real-time PCR for DNA extracted from oral swabs were 74.2% and 93.3%, respectively. Thus, oral swab samples are not suitable for breakthrough varicella diagnosis. Although DermaQuick® VZV is considered the most convenient point-of-care test for varicella, its sensitivity and specificity were lower than those of direct VZV LAMP.

Implementing vaccination policies based upon scientific evidence in Japan

The theme of the 24th Annual Meeting of the Japanese Society for Vaccinology was “Sustainable Future Medical Care Created by Vaccines.” This theme includes topics such as the proposal to reduce the medical costs incurred by societies with aging populations through prophylactic vaccination. The coronavirus disease 2019 (COVID-19) pandemic alerted us to the important roles that preventive measures, such as vaccines, play in fighting infectious diseases. In order to inform the public of the benefits of vaccines, it is important to provide society with information regarding new vaccine developments, adjuvants, the cost–benefit ratio of vaccine introduction, and vaccine effectiveness and safety. Clinical research is essential for obtaining evidence of vaccine effectiveness and safety. The United States Centers for Disease Control and Prevention (CDC) conducts active surveillance in defined areas before and after the introduction of vaccines and documents the reduction in infection rates as a measure of vaccine effectiveness. However, vaccine efficacy and side effects may vary by country and ethnicity. Therefore, it is necessary for individual countries to develop their own evidence-based surveillance programs. We have studied vaccine efficacy and documented side-effects observed in patients for the varicella and rotavirus vaccines in Japan. This review outlines the importance of providing scientific evidence for vaccine effectiveness and safety.

Trend in varicella patients 4 years after implementation of universal two-dose varicella vaccination in Japan

OBJECTIVE

To elucidate the trend and clinical spectrum of virologically diagnosed varicella patients after implementation of universal vaccination as a national immunization program in Japan.

PATIENTS AND METHODS

Study subjects were patients suspected of varicella, less than 15 years of age, who visited 14 pediatric clinics in the Nagoya VZV Study Group from September 2015 to August 2019. Practitioners collected patient samples and information such as backgrounds, clinical symptoms, and previous immunization status. All patients were confirmed as having varicella based on molecular diagnostic assays.

RESULTS

Varicella zoster virus (VZV) DNA was detected in swab samples from 506 (83.1%) of the 609 suspected patients. The 455 varicella patients for whom vaccination status was available were divided into two groups: 180 universal vaccination targets and 275 non-targets. Numbers of monthly varicella patients decreased gradually during the observation period. In the 2016/17 season, the seasonal epidemic of varicella became undetectable in the universal vaccination target group, and starting in the 2017/18 season, it was obscured even in the non-target group. The median age of patients was significantly lower in the universal vaccination target group (3 years) than the non-target group (7 years) (P < 0.001). Vaccination status differed significantly between the two groups (P < 0.001). Most varicella patients were in the non-target group, especially those who had been vaccinated once (60.4%). Frequency of fever (P < 0.001) and number of skin rashes at the time of the first hospital visit (P = 0.001) were significantly higher in the non-target group.

CONCLUSIONS

Although the number of childhood varicella patients declined after implementation of national immunization with two doses of varicella vaccination, sporadic outbreaks still occurred, mainly in the non-universal vaccination target group. Insufficient vaccination of members of this group is likely to be a major reason for small local outbreaks.