Pediatric population (aged 3-11 years) received primary inactivated SARS-CoV-2 vaccination prior to infection exhibiting robust humoral immune response following infected with Omicron variant: a study conducted in Beijing.

Objective: Analysis of SARS-CoV-2 IgG antibody and neutralizing antibody levels following SARS-CoV-2 infection in children aged 3-11 years, comparing those who had received the inactivated SARS-CoV-2 vaccine to those who were unvaccinated prior to infection, provides evidence for public health centers in formulating vaccination strategies and control policies. Methods: A study was conducted on children who visited the Children's Hospital, Capital Institute of Pediatrics from January 10, 2023 to March 31, 2023 (Beijing, China). Participants or their guardians completed a survey questionnaire providing information about their SARS-CoV-2 infection history and vaccination status. Serum samples were collected for testing of SARS-CoV-2 immunoglobulin G (IgG) and neutralizing antibodies (Nabs), which were performed using chemiluminescence immunoassay. Results: The study included 1,504 children aged 3-11 years with previous SARS-CoV-2 infection history. Among the 333 unvaccinated children, the serum SARS-CoV-2 IgG antibody level was median 2.30 (IQR, 1.27-3.99). However, children received one dose (78 cases) and two doses (1093 cases) of the inactivated vaccine prior to infection showed significantly higher SARS-CoV-2 IgG antibody levels, with values of median 10.11 (IQR, 8.66-10.93) and median 10.58 (IQR, 9.79-11.07), respectively. As to the unvaccinated children, 70.3% (234/333) were negative for SARS-CoV-2 Nabs, which were less than 6.00AU/ml. The remaining 29.7% (99/333) showed relatively low levels of Nabs, ranging from 6.00 to 50.00AU/ml. In contrast, for children who had received two doses of vaccine prior to infection, an overwhelming 99.3% (1086/1093) exhibited high levels of Nas in the range of 100.00-120.00 AU/ml. Remarkably, these elevated Nab levels persisted for at least a period of 3 months post-infection in children who had received two doses of inactivated SARS-CoV-2 vaccine prior to infection, regardless of age or sex and vaccine manufacturer. Conclusion: The administration of two doses of inactivated SARS-CoV-2 vaccine prior to infection has been shown to significantly enhance humoral immunity following SARS-CoV-2 infection in pediatric populations, producing adequate Nabs that persist at elevated levels for up to 3 months post-infection. For unvaccinated children who displayed weak humoral immunity following a primary natural infection, timely vaccination is recommended to bolster their immunization protection. The findings underscore the importance of vaccination in strengthening immune responses and protecting pediatric populations against SARS-CoV-2 infection.

Post-vaccination SARS-CoV-2 seroprevalence in children aged 3-11 years and the positivity in unvaccinated children: A retrospective, single-center study.

Objective: To analyze the positivity and levels of SARS-CoV-2 antibodies in vaccinated children to evaluate the humoral immune response of vaccination on pediatric population. Analysis on the causes of antibody positivity in unvaccinated children. Methods: A retrospective study was conducted on children who were admitted to the Children's Hospital Affiliated to Capital Institute of Pediatrics. The clinical data of serological testing of SARS-CoV-2 immunoglobulin M (IgM) and IgG antibodies were collected from SARS-CoV-2 vaccinated or unvaccinated children with no evidence of prior novel coronavirus infection. Chemiluminescence immunoassay was utilized for the in vitro determination of SARS-CoV-2 antibodies. Results: A total of 3,321 healthy children aged 6-11 years received two doses of inactivated SARS-CoV-2 vaccine. At 1 month after the second dose, the positive rate (96.5%) and levels [8.039 (interquartile range (IQR), 6.067-9.098)] of SARS-CoV-2 IgG antibodies reached the peak and remained at a high level for 2-3 months, after which the positive rate and level of vaccine-induced IgG antibody gradually decreased. Compared with 1 month after the second dose of vaccine, the positive rate of IgG antibody decreased to 70.4% at 7 months, and the antibody level decreased by 69.0%. A total of 945 children aged 3-5 years received one or two doses of inactivated vaccine. The positive rate and levels of SARS-CoV-2 IgG antibody in participants remained high for 3 months after vaccination. There was no gender-based difference in positive rate of IgG antibody in children aged 3-11 years old (P>0.05). Among the 5,309 unvaccinated children aged 0 day to 11 years, 105 (2.0%) were positive for SARS-CoV-2 IgG antibody, which was associated with passive infusion. The maternal humoral response to COVID-19 vaccination in noninfected pregnant women was transferred through the placenta to the fetus, and some children obtained SARS-CoV-2-positive antibodies through blood transfusion. Conclusions: Inactivated SARS-CoV-2 vaccines could induce robust humoral immune response that gradually declined within several months after the second dose. Therefore, it helps to determine whether children receive a booster dose and elicit a long-term memory immune response. Positive SARS-CoV-2 antibodies in unvaccinated children were associated with passive IgG antibody infusion.

The Prevalence of Mycoplasma Pneumoniae Among Children in Beijing Before and During the COVID-19 Pandemic.

Objective: Mycoplasma pneumoniae (M. pneumoniae) is an important pathogen of community acquired pneumonia. With the outbreak of coronavirus disease 2019 (COVID-19), the prevalence of some infectious respiratory diseases has varied. Epidemiological features of M. pneumoniae in children from Beijing (China) before and during the COVID-19 pandemic were investigated. Methods: Between June 2016 and May 2021, a total of 569,887 children with respiratory infections from Children's Hospital Affiliated to Capital Institute of Pediatrics (Beijing, China) were included in this study. M. pneumoniae specific-IgM antibody in serum specimens of these patients was tested by a rapid immunochromatographic assay kit. The relevant clinical data of M. pneumoniae-positive cases were also collected, and analyzed by RStudio software. Results: The results showed that 13.08% of collected samples were positive for M. pneumoniae specific-IgM antibody. The highest annual positive rate was 17.59% in 2019, followed by 12.48% in 2018, 12.31% in 2017, and 11.73% in 2016, while the rate dropped to 8.9% in 2020 and 4.95% in 2021, with significant difference. Among the six years, the positive rates in summer and winter seasons were significantly higher than those in spring and autumn seasons (p < 0.001). The positive rate was the highest in school-age children (22.20%), and lowest in the infant group (8.76%, p < 0.001). The positive rate in boys (11.69%) was lower than that in girls (14.80%, p < 0.001). There were no significant differences in different seasons, age groups, or genders before and during the COVID-19 pandemic (p > 0.05). Conclusions: Our study demonstrated that an M. pneumoniae outbreak started from the summer of 2019 in Beijing. After the COVID-19 pandemic outbreak in the end of 2019, the M. pneumoniae positive rates dropped dramatically. This may be due to the restrictive measures of the COVID-19 pandemic, which effectively controlled the transmission of M. pneumoniae. The relationships between M. pneumoniae positive rates and season, age, and gender were not statistically significant before and during the COVID-19 pandemic.

Diagnostic Value of Serum ELISA of Mycoplasma Pneumoniae IgM and IgG and Passive Particle Agglutination for Mycoplasma Pneumoniae Pneumonia in Children.

BACKGROUND: The study was aimed to compare ELISA results of Mycoplasma pneumoniae IgG (MP-IgG) and Mycoplasma pneumoniae IgM (MP-IgM) with the passive particle agglutination (PA) test, as well as to evaluate their application value in the diagnosis of Mycoplasma pneumoniae pneumonia (MPP) in children. METHODS: Serum MP antibodies were detected by ELISA for MP-IgM, MP-IgG, and PA for 292 patients in the MPP group and 89 patients in NMP group. The PA results were used as reference standards. These patients were treated in the respiratory department of Children's Hospital Capital Institute of Pediatrics, China, from July to December, 2019. RESULTS: In the MPP group, the positive rate for MP-IgM was 75% higher than that of the PA titer (73.97%), Pearson's coefficient was 0.711, and the Kappa coefficient was 0.662, p < 0.01, suggesting that both the correlation and the consistency of the two methods were high. In the PA-negative group (< 1:160), 22.38% of patients were MP-IgM positive, indicating that the sensitivity to MP-IgM was higher compared to PA, when the disease duration was less than 7 days. The diagnostic value for MP-IgG was lower than that for MP-IgM, and the high positive rate of MP-IgG (48.31%) in the NMP group suggested a high background value of MP-IgG in children. Testing of paired serum obtained a more accurate diagnosis. At admission, 47.57% of patients with paired serum who were negative for MP-IgM, converted to a net positive after 4 - 6 days, except for one patient. In the paired serum, 57.8% of patients had a 4-fold increase of MP-IgG. CONCLUSIONS: MP-IgM was a sensitive indicator of MP infection in children with a high consistency and correlation with the reference positive standard of PA titer ≥ 1:160. For a more accurate diagnosis, testing of paired serum is still necessary, and a 4-fold increase in MP-IgG could be the supplementary diagnosis method.

Inductively Coupled Plasma Mass Spectrometry as a Reference Method to Evaluate Serum Calcium Measurement Bias and the Commutability of Processed Materials during Routine Measurements.

BACKGROUND: Measuring total serum calcium is important for the diagnosis of diseases. Currently, results from commercial kits for calcium measurement are variable. Generally, the performance of serum calcium measurements is monitored by external quality assessment (EQA) or proficiency testing schemes. However, the commutability of the EQA samples and calibrators is often unknown, which limits the effectiveness of EQA schemes. The aim of this study was to evaluate the bias of serum calcium measurements and the commutability of processed materials. METHODS: Inductively coupled plasma mass spectrometry was applied as a comparative method, and 14 routine methods were chosen as test methods. Forty-eight serum samples from individual patients and 25 processed materials were quantified. A scatter plot was generated from patient samples, and 95% prediction intervals were calculated to evaluate the commutability of the processed materials and measurement bias at three concentration levels was used to determine the accuracy of routine assays. RESULTS: All assays showed high precision (total coefficient of variation [CV] <2.26%) and correlation coefficients (r > 0.99). For all assays, the mean bias for the 48 patient samples ranged from -0.13 mmol/L to 0.00 mmol/L (-5.61-0.01%), and the ranges for the three concentrations were -0.10-0.04 mmol/L (-5.71-2.35%), -0.14--0.01 mmol/L (-5.80--0.30%), and -0.19-0.04 mmol/L (-6.24-1.22%). The EQA samples, calibrators, and animal sera exhibited matrix effects in some assays; human serum pools were commutable in all assays; certificate reference materials were commutable in most assays, and only GBW09152 exhibited a matrix effect in one assay; and aqueous reference materials exhibited matrix effects in most assays. CONCLUSIONS: Biases for most assays were within the acceptable range, although the accuracy of some assays needs improvement. Human serum pools prepared from patient samples were commutable, and the other tested materials exhibited a matrix effect.

Determination of serum calcium levels by 42Ca isotope dilution inductively coupled plasma mass spectrometry.

BACKGROUND: Serum calcium level is an important clinical index that reflects pathophysiological states. However, detection accuracy in laboratory tests is not ideal; as such, a high accuracy method is needed. METHODS: We developed a reference method for measuring serum calcium levels by isotope dilution inductively coupled plasma mass spectrometry (ID ICP-MS), using 42Ca as the enriched isotope. Serum was digested with 69% ultrapure nitric acid and diluted to a suitable concentration. The 44Ca/42Ca ratio was detected in H2 mode; spike concentration was calibrated by reverse IDMS using standard reference material (SRM) 3109a, and sample concentration was measured by a bracketing procedure. We compared the performance of ID ICP-MS with those of three other reference methods in China using the same serum and aqueous samples. RESULTS: The relative expanded uncertainty of the sample concentration was 0.414% (k=2). The range of repeatability (within-run imprecision), intermediate imprecision (between-run imprecision), and intra-laboratory imprecision were 0.12%-0.19%, 0.07%-0.09%, and 0.16%-0.17%, respectively, for two of the serum samples. SRM909bI, SRM909bII, SRM909c, and GBW09152 were found to be within the certified value interval, with mean relative bias values of 0.29%, -0.02%, 0.10%, and -0.19%, respectively. The range of recovery was 99.87%-100.37%. Results obtained by ID ICP-MS showed a better accuracy than and were highly correlated with those of other reference methods. CONCLUSIONS: ID ICP-MS is a simple and accurate candidate reference method for serum calcium measurement and can be used to establish and improve serum calcium reference system in China.

A candidate reference method for serum calcium measurement by inductively coupled plasma mass spectrometry.

BACKGROUND: Calcium is an important serum ion which is frequently assayed in clinical laboratories. Since quality assurance requires reference methods, the establishment of a candidate reference method for serum calcium measurement is important. METHOD: An inductively coupled plasma mass spectrometry (ICP-MS) method was developed. Serum samples were spiked gravimetrically with aluminum internal standard, digested with 69% ultrapure nitric acid and diluted to test concentration. Then the (44)Ca/(27)Al ratios were measured by ICP-MS in hydrogen mode. The method was calibrated using 5% nitric acid matrix calibrators and the calibration function was established with bracketing method. RESULTS: The correlation coefficients between the measured (44)Ca/(27)Al ratios and the analyte concentrations ratios were all >0.9999. The coefficients of variation of the measurements were 0.27% and 0.16% for two spiked serum. The analytical recovery was 100.24%. The accuracy of the measurement was also verified through measurement of certified reference materials. Comparison with recognized reference method and international inter-laboratory comparisons gave satisfied results. CONCLUSION: New ICP-MS method is specific, precise, simple, and low in cost, and may be used as a candidate reference method in the standardization of serum calcium measurement.

Evaluation of the Bias of Serum Magnesium Measurements and the Commutability of Processed Materials.

BACKGROUND: Measuring serum magnesium plays an important role in the diagnosis of diseases. The performance of serum magnesium measurements is most conveniently monitored by external quality assessment (EQA) or proficiency testing (PT) schemes. However, the commutability of EQA samples and calibrators is often unknown, and the effectiveness of EQA schemes is limited. We designed the present study to evaluate the matrix effects of processed materials and the accuracy of routine methods. METHODS: Inductively coupled plasma mass spectrometry was applied as a comparative method, and 12 routine methods composed of 12 kits, their supporting calibrators, and a Hitachi 7180 automatic analyzer were chosen as the test methods. Serum from 48 single patients and 24 processed materials were quantified by the comparative and routine methods. The 95% prediction intervals and relative bias were calculated at three medical decision levels (0.60 mmol/L, 1.00 mmol/L, and 2.50 mmol/L) according to EP9-A2 and EP14-A2. The commutability of the materials was evaluated by comparing the values of the processed materials with the limit bias, and the accuracy of the routine methods was evaluated by the relative bias. RESULTS: The precision of all of the assays was good (total CV < 2.01%), and the decision coefficients were high, most were greater than 0.99. The 2013 and 2014 EQA samples showed positive matrix effects in some of the assays; the human serum pools were commutable in all of the assays; the certified reference materials were commutable in most of the assays; the calibrators showed matrix effects in some of the assays; the aqueous reference materials showed matrix effects in most of the assays and could only be used in the reference methods. For all of the assays, the range of the mean bias was -0.04 - 0.06 mmol/L (-4.52% - 7.20%), and the range of the expected bias at the three medical decision levels was -0.03 - 0.06 mmol/L (-4.27% - 9.30%) at 0.6 mmol/L, -0.05 - 0.06 mmol/L (-4.79% - 6.31%) at 1.00 mmol/L, and -0.364 - 0.10 mmol/L (-13.66% - 4.05%) at 2.50 mmol/L. CONCLUSIONS: For most of the assays, the biases were in an acceptable range, whereas the accuracy of some of the assays needs improvement. Human serum pools prepared from patient samples were commutable, and other materials still exhibited matrix effects.

Performance of electrolyte measurements assessed by a trueness verification program.

BACKGROUND: In this study, we analyzed frozen sera with known commutabilities for standardization of serum electrolyte measurements in China. METHODS: Fresh frozen sera were sent to 187 clinical laboratories in China for measurement of four electrolytes (sodium, potassium, calcium, and magnesium). Target values were assigned by two reference laboratories. Precision (CV), trueness (bias), and accuracy [total error (TEa)] were used to evaluate measurement performance, and the tolerance limit derived from the biological variation was used as the evaluation criterion. RESULTS: About half of the laboratories used a homogeneous system (same manufacturer for instrument, reagent and calibrator) for calcium and magnesium measurement, and more than 80% of laboratories used a homogeneous system for sodium and potassium measurement. More laboratories met the tolerance limit of imprecision (coefficient of variation [CVa]) than the tolerance limits of trueness (biasa) and TEa. For sodium, calcium, and magnesium, the minimal performance criterion derived from biological variation was used, and the pass rates for total error were approximately equal to the bias (<50%). For potassium, the pass rates for CV and TE were more than 90%. Compared with the non homogeneous system, the homogeneous system was superior for all three quality specifications. CONCLUSIONS: The use of commutable proficiency testing/external quality assessment (PT/EQA) samples with values assigned by reference methods can monitor performance and provide reliable data for improving the performance of laboratory electrolyte measurement. The homogeneous systems were superior to the non homogeneous systems, whereas accuracy of assigned values of calibrators and assay stability remained challenges.