Cho HK, et al. J Korean Med Sci. 2016 Dec;31(12):1957-1962. https://doi.org/10.3346/jkms.2016.31.12.1957

Although there have been several studies regarding the immunogenicity of one or two booster doses of the measles–mumps–rubella (MMR) vaccine in measles-seronegative young adults, limited data are available about how long the immune response is sustained compared with natural infection. This study included seronegative healthcare workers (HCWs) (aged 21–38 years) who received one or two doses of the measles–mumps–rubella (MMR) vaccine and HCWs with laboratory-confirmed measles infection during an outbreak in 2019. We compared neutralizing antibody titers measured using the plaque reduction neutralization (PRN) test and measles-specific immunoglobulin G (IgG) using chemiluminescent immunoassays 2 years after vaccination or infection. Among 107 HCWs with seronegative measles IgGs, the overall seroconversion rate of measles IgGs remained 82.2% (88/107), and 45.8% (49/107) of the participants had a medium (121–900) or high (>900) PRN titer after 2 years from one or two booster doses. The measles-neutralizing antibody titers of both PRN titer (ND50) and geometric mean concentration 2 years after natural infection were significantly higher than those of one or two booster doses of the MMR vaccine (p < 0.001 and p < 0.001, respectively). Our results suggest that serologic screening followed by appropriate postexposure prophylaxis can be beneficial for young HCWs without a history of natural infection especially in a measles outbreak setting, because of possible susceptibility to measles despite booster MMR vaccination 2 years ago. Long-term data about sustainable humoral immunity after one or two booster vaccination are needed based on the exact vaccination history.

Kim HW, et al. J Korean Med Sci. 2017 Jul;32(7):1111-1117. https://doi.org/10.3346/jkms.2017.32.7.1111

Lee S, et al. J Korean Med Sci. 2016 Dec;31(12):1937-1942. https://doi.org/10.3346/jkms.2016.31.12.1937

Herpes zoster (HZ) is caused by latent varicella-zoster virus (VZV) reactivation when VZV-specific cell-mediated immunity declines. Information on HZ in children is limited. Therefore, we retrospectively investigated HZ’s clinical course and complications in children. We extracted the outpatient and hospitalization medical records of pediatric patients (<19 years) primarily diagnosed with HZ (ICD-10 B02 code) between January 2010 and November 2020. HZ was defined as a typical unilateral dermatomal vesicular rash where HZ was the treating physician’s primary diagnosis. Recognized HZ complications included combined bacterial skin infection, ophthalmic zoster, zoster oticus without facial paralysis, meningitis, and PHN. We identified 602 HZ cases, among which 54 developed HZ complications and were included in our analysis. The median age was 14.7 years, most patients were aged ≥13 years (42, 79%), and none were aged <4 years. Fifty-three were immunocompetent, and only one had systemic lupus erythematosus. The most frequent complication was zoster ophthalmicus (n = 26, 48%). HZ complications were also observed in immunocompetent or vaccinated children exhibiting a head or neck rash before and after VZV immunization. Current VZV vaccination programs may be insufficient in preventing HZ complications. Therefore, close varicella and HZ burden monitoring and the establishment of effective VZV vaccination programs are imperative.

The protective capacities of antibodies induced with Haemophilus influenzae type b (Hib) vaccines can be directly assessed in vitro with a Hib-specific serum bactericidal assay (SBA). However, the conventional SBA requires several tedious steps including manual counting of bacterial colonies, and therefore, it is seldom used. To overcome these limitations, we have improved the conventional SBA by using frozen target bacteria and by developing an automated colony counting method based on agar plates with the chromogenic dye 2, 3, 5-triphenyl tetrazolium chloride (TTC). These changes enabled us to analyze about 100 serum samples per day per person by SBA. When the intra- and inter-assay precisions were studied, this assay showed a coefficient of variation (CV) ranging from 1 to 38 %. To monitor the long term assay stability for assays involving different bacteria lots, complement lots, and operators, we analyzed bactericidal indices of quality control samples obtained over a 6 year period and found the CV to be about 35–50 %. Lastly, our SBA results were compared with the ELISA results obtained using 90 serum samples from children. We showed that the bactericidal index correlated with IgG anti-Hib antibody levels (r = 0.84), with a bactericidal index of 10 corresponding approximately to 0.15 μg/mL IgG, the widely accepted protective level of antibody. We describe a simple high throughput SBA for anti-Hib antibodies that would be useful for evaluating various Hib vaccines. While additional work will be needed to standardize the assay, this SBA should greatly facilitate studies of Hib vaccines.