A bead-based multiplex assay covering all coronaviruses pathogenic for humans for sensitive and specific surveillance of SARS-CoV-2 humoral immunity

Serological assays measuring antibodies against SARS-CoV-2 are key to describe the epidemiology, pathobiology or induction of immunity after infection or vaccination. Of those, multiplex assays targeting multiple antigens are especially helpful as closely related coronaviruses or other antigens can be analysed simultaneously from small sample volumes, hereby shedding light on patterns in the immune response that would otherwise remain undetected. We established a bead-based 17-plex assay detecting antibodies targeting antigens from all coronaviruses pathogenic for humans: SARS-CoV-2, SARS-CoV, MERS-CoV, HCoV strains 229E, OC43, HKU1, and NL63. The assay was validated against five commercial serological immunoassays, a commercial surrogate virus neutralisation test, and a virus neutralisation assay, all targeting SARS-CoV-2. It was found to be highly versatile as shown by antibody detection from both serum and dried blot spots and as shown in three case studies. First, we followed seroconversion for all four endemic HCoV strains and SARS-CoV-2 in an outbreak study in day-care centres for children. Second, we were able to link a more severe clinical course to a stronger IgG response with this 17-plex-assay, which was IgG1 and IgG3 dominated. Finally, our assay was able to discriminate recent from previous SARS-CoV-2 infections by calculating the IgG/IgM ratio on the N antigen targeting antibodies. In conclusion, due to the comprehensive method comparison, thorough validation, and the proven versatility, our multiplex assay is a valuable tool for studies on coronavirus serology.

SARS-CoV-2 seroconversion in children attending daycare versus adults in Germany between October 2020 and June 2021

BACKGROUND

Data on seroconversion rates after SARS-CoV-2 infection in young children (<6 years) is scarce. The present study compares seroconversion rates between young children and adults and identifies associated factors.

METHODS

The COALA study ("Corona-outbreak-related examinations in daycare centers") investigated transmission dynamics of SARS-CoV-2 in daycare centers and associated households (10/2020-06/2021). 114 individuals tested positive for SARS-CoV-2 through PCR either prior to the study period by health authorities or in PCR testing during the study period. Two capillary blood samples were obtained within five weeks consecutively and tested for SARS-CoV-2 IgG-antibodies (second sampling depending on positive PCR). Results from 91 participants (38 young children 1-6 years, 53 adults) were included in the analyses.

RESULTS

Seroconversion rate in young children is significantly higher than in adults (97.4% versus 66%). High viral load and longer time interval between the probable date of infection and antibody testing are associated with seroconversion.

CONCLUSIONS

Our findings depict substantial development of specific antibodies in young children after SARS-CoV-2 infection. This may provide temporary protection from re-infection for young children or severe disease for this age group.

Symptomatik einer akuten SARS-CoV-2-Infektion bei Kindern im Kita-Alter

Hintergrund

Die Symptomatik einer pädiatrischen SARS-CoV-2-Infektion ist sehr variabel. Es gibt nur wenige Studien zu nichthospitalisierten Kindern bzw. Kindern im Kita-Alter.

Ziel der Arbeit

Die Arbeit soll die Häufigkeit verschiedener COVID-19-Symptome bei ein- bis 6‑jährigen Kindern beschreiben. Sie führt dazu Daten aus 2 Modulen der Corona-KiTa-Studie zusammen: 1) das Modul „COALA“ – Corona: Anlassbezogene Untersuchungen in Kitas und 2) das Modul „CATS“ – Corona KiTa Surveillance (Meldedaten).

Material und Methoden

In COALA wurden die Infektionsgeschehen in 30 Kitas, in denen ein SARS-CoV-2-Fall gemeldet wurde, untersucht (Oktober 2020 bis Juni 2021). Kita-Kinder wurden prospektiv über 12 Tage beobachtet (SARS-CoV-2-Tests, Symptomtagebuch). Die Ergebnisse wurden mit den Symptomangaben der deutschlandweit gemeldeten SARS-CoV-2-Fälle (Meldedaten) verglichen.

Ergebnisse

Aus den teilnehmenden Kitas liegen für 289 Kinder Angaben vor. Von 39 Kindern mit SARS-CoV‑2 (Wildtyp, α‑Variante) hatten 64 % mindestens ein Symptom, von den nicht mit SARS-CoV‑2 infizierten Kindern 40 %. In beiden Gruppen war Schnupfen das häufigste Symptom (36 % vs. 25 %, n. s.). Aus den Meldedaten liegen für 84.371 Kinder klinische Informationen vor, Fieber war am häufigsten (27 %), neben Schnupfen (26 %). Schwere Beschwerden wie z. B. Atemnot wurden in den Ausbruchsuntersuchungen und in den Meldedaten nur selten angegeben (3 % bzw. 1 %).

Schlussfolgerung

Kinder im Kita-Alter haben meist milde bzw. asymptomatische Verläufe einer SARS-CoV-2-Infektion. Ihre Symptome ähneln denjenigen von nicht mit SARS-CoV‑2 infizierten Kindern aus denselben Kitas. Es erscheint sinnvoll, Erkenntnisse aus den Meldedaten durch Ausbruchsuntersuchungen zu ergänzen, um methodische Limitationen der einzelnen Vorgehensweisen auszugleichen.

Zusatzmaterial online

Die Online-Version dieses Beitrags (10.1007/s00112-022-01640-3) enthält eine weitere Tabelle, die Symptome bei symptomatischen SARS-CoV-2-Fällen von Kindern im Alter von einem bis 6 Jahren in der COALA-Stichprobe und in den Meldedaten gegenüberstellt.

SARS-CoV-2 viral clearance and viral load kinetics in young children (1-6 years) compared to adults: Results of a longitudinal study in Germany

OBJECTIVE

To investigate SARS-COV-2 viral clearance and viral load kinetics in the course of infection in children aged 1-6 years in comparison with adults.

METHODS

Prospective cohort study of infected daycare children and staff and their close contacts in households from 11/2020 to 06/2021. Adult participants took upper respiratory tract specimen from themselves and/or their children, for PCR tests on SARS-CoV-2. Data on symptoms and exposure were used to determine the date of probable infection for each participant. We determined (a) viral clearance, and (b) viral load dynamics over time. Samples were taken from day 4-6 to day 16-18 after diagnosis of the index case in the respective daycare group (5 samples per participant).

RESULTS

We included 40 children (1-6 years) and 67 adults (18-77 years) with SARS-CoV-2 infection. Samples were available at a mean of 4.3 points of time per participant. Among the participants, the 12-day study period fell in different periods within the individual course of infection, ranging from day 5-17 to day 15-26 after assumed infection.Children reached viral clearance at a median of 20 days after assumed infection (95% CI 17-21 days, Kaplan-Meier Analysis), adults at 23 days (95% CI 20-25 days, difference not significant). In both children and adults, viral load decreased over time with trajectories of the mean viral load not being statistically different between groups. Kaplan-Meier calculations show that from day 15 (95% CI 13-15), 50% of all participants had a viral load <1 million copies/ml, i.e. were no longer infectious or negative.

CONCLUSION

Children aged 1-6 and adults infected with SARS-CoV-2 (wild type and Alpha variant) did not differ significantly in terms of viral load kinetics and time needed to clear the virus. Therefore, containment measures are important also in the daycare settings as long as the pandemic continues.

SARS-CoV-2 Transmissibility Within Day Care Centers-Study Protocol of a Prospective Analysis of Outbreaks in Germany

Introduction: Until today, the role of children in the transmission dynamics of SARS-CoV-2 and the development of the COVID-19 pandemic seems to be dynamic and is not finally resolved. The primary aim of this study is to investigate the transmission dynamics of SARS-CoV-2 in child day care centers and connected households as well as transmission-related indicators and clinical symptoms among children and adults. Methods and Analysis: COALA ("Corona outbreak-related examinations in day care centers") is a day care center- and household-based study with a case-ascertained study design. Based on day care centers with at least one reported case of SARS-CoV-2, we include one- to six-year-old children and staff of the affected group in the day care center as well as their respective households. We visit each child's and adult's household. During the home visit we take from each household member a combined mouth and nose swab as well as a saliva sample for analysis of SARS-CoV-2-RNA by real-time reverse transcription polymerase chain reaction (real-time RT-PCR) and a capillary blood sample for a retrospective assessment of an earlier SARS-CoV-2 infection. Furthermore, information on health status, socio-demographics and COVID-19 protective measures are collected via a short telephone interview in the subsequent days. In the following 12 days, household members (or parents for their children) self-collect the same respiratory samples as described above every 3 days and a stool sample for children once. COVID-19 symptoms are documented daily in a symptom diary. Approximately 35 days after testing the index case, every participant who tested positive for SARS-CoV-2 during the study is re-visited at home for another capillary blood sample and a standardized interview. The analysis includes secondary attack rates, by age of primary case, both in the day care center and in households, as well as viral shedding dynamics, including the beginning of shedding relative to symptom onset and viral clearance. Discussion: The results contribute to a better understanding of the epidemiological and virological transmission-related indicators of SARS-CoV-2 among young children, as compared to adults and the interplay between day care and households.