Immune responses to SARS-CoV-2 infection and vaccination in children

A genetically modulated Toll-like receptor-tolerant phenotype in peripheral blood cells of children with multisystem inflammatory syndrome

Dysregulated innate immune responses contribute to multisystem inflammatory syndrome in children (MIS-C), characterized by gastrointestinal, mucocutaneous, and/or cardiovascular injury occurring weeks after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exposure. To investigate innate immune functions, we stimulated ex vivo peripheral blood cells from MIS-C patients with agonists of Toll-like receptors (TLR), key innate immune response initiators. We found severely dampened cytokine responses and elevated gene expression of negative regulators of TLR signaling. Increased plasma levels of zonulin, a gut leakage marker, were also detected. These effects were also observed in fully convalescent children months after MIS-C recovery. When we investigated the genetic background of patients in relation to TLR responsiveness, we found that cells from MIS-C children carrying rare heterozygous variants of lysosomal trafficking regulator (LYST) were less refractory to TLR stimulation and exhibited lysosomal and mitochondrial abnormalities with altered energy metabolism. Moreover, these rare LYST variant heterozygous carriers tended to exhibit unfavorable clinical laboratory indicators of inflammation, including more profound lymphopenia. The results of our observational study have several implications. First, TLR hyporesponsiveness may be associated with hyperinflammation and/or excessive or prolonged stimulation with gut-originated TLR ligands. Second, TLR hyporesponsiveness during MIS-C may be protective, since LYST variant heterozygous carriers exhibited reduced TLR hyporesponsiveness and unfavorable clinical laboratory indicators of inflammation. Thus, links may exist between genetic background, ability to establish a refractory immune state, and MIS-C clinical spectrum. Third, the possibility exists that prolonged TLR hyporesponsiveness is one of the mechanisms driving long coronavirus disease (COVID), which highlights the need to monitor long-term consequences of MIS-C.

Dynamic changes in the circulation of respiratory pathogens in children during and after the containment of the 2019 coronavirus disease pandemic in Kunming, China

PURPOSE

We aimed to determine the changes in the frequency of respiratory pathogens and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during containment of the 2019 coronavirus disease pandemic and elucidate the epidemiological interference that may have occurred after lifting pandemic measures.

METHODS

A total of 4,770 Nasopharyngeal swab samples were collected from children with ARTIs from the First People's Hospital of Yunnan Province between January 2022 and December 2023 and subjected to nucleic acid testing for 13 types of respiratory pathogens and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

RESULTS

The frequency of pathogens among children from 2020 to 2022 was in the following order: HRV > Mp > HADV > H3N2 > HMPV and HRV > HRSV > HPIV > H1N1 > H3N2. In weeks 1 to 3 of 2023, the frequency of pathogens significantly declined, and then H1N1 rebounded significantly in 2023. HRV, HRSV, and H3N2 showed a shift in the season of high frequency. Patterns of multi-pathogen infections were more complex in 2023 than in 2022, with HRV having a higher frequency and co-infection rate than other pathogens. These changes may have been associated with interference caused by the resurgence of SARS-CoV-2 prevalence, in addition to being influenced by changes in pandemic containment and lifting measures.

CONCLUSIONS

The frequency rate of common respiratory pathogens among children was not significantly different and remained high. The study findings help elucidate the aforementioned unique historical period and effectively control respiratory tract infections to reduce the harm to pediatric health caused by respiratory pathogens.

The effect of COVID-19 vaccination on symptomatic infection and related symptoms among preterm-born children aged 3-7 years in China

Vaccination plays a crucial role in preventing and controlling SARS-CoV-2 infections as well as their associated adverse outcomes. But there is a notable lack of research on the effectiveness of COVID-19 vaccination in children, particularly those young preterm-born children, who are more vulnerable to severe outcomes from SARS-CoV-2 infection. We aimed to determine the effect of vaccination with inactivated vaccines BBIBP-CorV and CoronaVac on symptomatic COVID-19 infection and related symptoms in preterm-born children aged 3-7 years after relaxation of the COVID-19 prevention and control measures in December 2022 in China. We performed a retrospective cohort study involving 242 preterm-born children aged 3-7 years and the data were collected in March 2023. Logistic regression models and modified Poisson regression models combined with entropy balancing were used to explore the associations of vaccination against SARS-CoV-2 with symptomatic COVID-19, specific symptoms, and persistent symptoms one month after recovery from COVID-19. Of the 242 recruited preterm-born children, 156 (64.5%) were vaccinated with inactivated vaccines BBIBP-CorV and CoronaVac. After entropy balancing, the covariates were balanced between the vaccinated and the unvaccinated groups, with standardized mean difference < 0.001. Vaccination with the said SARS-CoV-2 vaccines lowered the risk of developing symptomatic COVID-19 in preterm-born children (risk ratio [RR] = 0.783; 95% confidence interval [CI]: (0.711, 0.861). Likewise, COVID-19 vaccination was associated with a decline in the risk of pneumonia (odds ratio [OR] = 0.318; 95% CI 0.110, 0.913), fever (RR = 0.710; 95% CI 0.635, 0.794), high fever (RR = 0.542; 95% CI 0.297, 0.988), sore throat (OR = 0.304; 95% CI 0.139, 0.664), and persistent symptoms (RR = 0.425; 95% CI 0.182, 0.993). Immunization with inactivated vaccines BBIBP-CorV and CoronaVac provides protection against symptomatic COVID-19 for preterm-born children 3-7 years.

Post-COVID-19 condition in children: epidemiological evidence stratified by acute disease severity

BACKGROUND

To determine the prevalence of pediatric Post-COVID-19 condition (PPCC), identify risk factors, and assess the quality of life in children with differing severities of acute COVID-19.

METHODS

During a prospective longitudinal study with a 1-year follow-up, we compared non-hospitalized (mild) and hospitalized (severe) COVID-19 cases to a negatively tested control group.

RESULTS

579 children were included in this study. Of these, 260 had mild acute disease (median age:8, IQR:6-10), 60 had severe acute disease (median age:1, IQR:0.1-4.0), and 259 tested negative for SARS-CoV-2 (NT) (median age:8, IQR:5-10). At three months, 14.6% of the SARS-CoV-2 positive mild group (RR:6.31 (CI 95%: 2.71-14.67)) and 29.2% of the severe group (RR:12.95 (CI 95%: 5.37-31.23)) reported sequelae, versus 2.3% of the NT group. PPCC prevalence in the mild group decreased from 16.1% at one month to 4.4% at one year. Children with PPCC exhibited lower physical health-related quality of life scores and higher fatigue scores than the NT children.

CONCLUSIONS

Severe acute COVID-19 in children leads to a higher PPCC prevalence than in mild cases. PPCC prevalence decreases over time. Risk factors at three months include prior medical history, hospital admission, and persistent fatigue one month after a positive test.

IMPACT

We demonstrate children with severe COVID-19 are more likely to develop Post-COVID-19 condition than those with mild or no infections, and highlights the risk factors. Here we have stratified by acute disease severity, prospectively included a negative control group, and have demonstrated the heterogeneity in prevalence when utilizing various recent definitions of post-COVID. Identifying risk factors for pediatric post-COVID and highlighting the heterogeneity in prevalence based on various current definitions for post-COVID should aid in correctly identifying potential pediatric post-COVID cases, aiding in early intervention.

Life-threatening infections in human newborns: Reconciling age-specific vulnerability and interindividual variability

In humans, the interindividual variability of clinical outcome following exposure to a microorganism is immense, ranging from silent infection to life-threatening disease. Age-specific immune responses partially account for the high incidence of infection during the first 28 days of life and the related high mortality at population level. However, the occurrence of life-threatening disease in individual newborns remains unexplained. By contrast, inborn errors of immunity and their immune phenocopies are increasingly being discovered in children and adults with life-threatening viral, bacterial, mycobacterial and fungal infections. There is a need for convergence between the fields of neonatal immunology, with its in-depth population-wide characterization of newborn-specific immune responses, and clinical immunology, with its investigations of infections in patients at the cellular and molecular levels, to facilitate identification of the mechanisms of susceptibility to infection in individual newborns and the design of novel preventive and therapeutic strategies.

A genetically modulated Toll-like-receptor-tolerant phenotype in peripheral blood cells of children with multisystem inflammatory syndrome

Dysregulated innate immune responses contribute to multisystem inflammatory syndrome in children (MIS-C), characterized by gastrointestinal, mucocutaneous, and/or cardiovascular injury occurring weeks after SARS-CoV-2 exposure. To investigate innate immune functions in MIS-C, we stimulated ex vivo peripheral blood cells from MIS-C patients with agonists of Toll-like receptors (TLR), key innate immune response initiators. We found severely dampened cytokine responses and elevated gene expression of negative regulators of TLR signaling. Increased plasma levels of zonulin, a gut leakage marker, were also detected. These effects were also observed in children enrolled months after MIS-C recovery. Moreover, cells from MIS-C children carrying rare genetic variants of lysosomal trafficking regulator (LYST) were less refractory to TLR stimulation and exhibited lysosomal and mitochondrial abnormalities with altered energy metabolism. Our results strongly suggest that MIS-C hyperinflammation and/or excessive or prolonged stimulation with gut-originated TLR ligands drive immune cells to a lasting refractory state. TLR hyporesponsiveness is likely beneficial, as suggested by excess lymphopenia among rare LYST variant carriers. Our findings point to cellular mechanisms underlying TLR hyporesponsiveness; identify genetic determinants that may explain the MIS-C clinical spectrum; suggest potential associations between innate refractory states and long COVID; and highlight the need to monitor long-term consequences of MIS-C.