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

Transmission risks of Omicron BA.5 following inactivated COVID-19 vaccines among children and adolescents in China

BACKGROUND

As SARS-CoV-2 Omicron variants circulating globally since 2022, assessing the transmission characteristics, and the protection of vaccines against emerging Omicron variants among children and adolescents are needed for guiding the control and vaccination policies.

METHODS

We conducted a retrospective cohort study for SARS-CoV-2 infections and close contacts aged <18 years from an outbreak seeded by Omicron BA.5 variants. The secondary attack rate (SAR) was calculated and the protective effects of two doses of inactivated vaccine (mainly Sinopharm /BBIBP-CorV) within a year versus one dose or two doses above a year after vaccination against the transmission and infection of Omicron BA.5 were estimated.

RESULTS

A total of 3442 all-age close contacts of 122 confirmed SARS-CoV-2 infections aged 0-17 years were included. The SAR was higher in the household setting and for individuals who received a one-dose inactivated vaccine or those who received a two-dose for more than one year, with estimates of 28.5% (95% credible interval [CrI]: 21.1, 37.7) and 55.3% (95% CrI: 24.4, 84.8), respectively. The second dose of inactivated vaccine conferred substantial protection against all infection and transmission of Omicron BA.5 variants within a year.

CONCLUSIONS

Our findings support the rollout of the second dose of inactivated vaccine for children and adolescents during the Omciron BA.5 predominant epidemic phase. Given the continuous emergence of SARS-CoV-2 variants, monitoring the transmission risk and corresponding vaccine effectiveness against SARS-CoV-2 variants among children and adolescents is important to inform control strategy.

Clinical manifestations and long-term symptoms associated with SARS-CoV-2 omicron infection in children aged 0-17 years in Beijing: a single-center study

Objective

The study aims to analyze the clinical characteristics of acute phase of SARS-CoV-2 infection in children aged 0-17 years with the Omicron variant, and summarize the persistent symptoms or new-onset clinical manifestations from 4 to 12 weeks after acute COVID. Explore the association between the vaccination status and SARS-CoV-2 neutralizing antibody levels post infection among preschool-aged children. The comprehensive study systematically describes the clinical characteristics of children infected with SARS-CoV-2, providing a foundation for diagnosis and evaluating long-term COVID in pediatric populations.

Methods

The study enrolled children who were referred to the Children's Hospital, Capital Institute of Pediatrics, (Beijing, China) from January 10, 2023 to March 31, 2023. Participants were classified as infant and toddlers, preschool, school-age, and adolescent groups. Children or their legal guardians completed survey questionnaires to provide information of previous SARS-CoV-2 infection history, as well as clinical presentation during the acute phase and long-term symptoms from 4 to 12 weeks following infection. Furthermore, serum samples were collected from children with confirmed history of SARS-CoV-2 infection for serological testing of neutralizing antibodies.

Results

The study recruited a total of 2,001 children aged 0-17 years who had previously tested positive for SARS-CoV-2 through nucleic acid or antigen testing. Fever emerged as the predominant clinical manifestation in 1,902 (95.1%) individuals with body temperature ranging from 37.3 to 40.0°C. Respiratory symptoms were identified as secondary clinical manifestations, with cough being the most common symptom in 777 (38.8%) children, followed by sore throat (22.1%), nasal congestion (17.8%), and runnning nose (17.2%). Fatigue (21.6%), headache (19.8%) and muscle-joint pain (13.5%) were frequently reported systemic symptoms in children. The proportion of children with symptoms of SARS-CoV-2 infection varied across age groups. 1,100 (55.0%) children experienced persistent symptoms from 4 to 12 weeks post the acute phase of infection. Trouble concentrating (22.1%), cough (22.1%), and fatigue (12.1%) were frequently reported across age groups in the extended period. A limited number of children exhibited cardiovascular symptoms with chest tightness, tachycardia, and chest pain reported by 3.5%, 2.5%, and 1.8% of children, respectively. Among 472 children aged 3-5 years, 208 children had received two doses of SARS-CoV-2 vaccine at least 6 months prior to infection, and no association was found between the incidence of long-term COVID and pre-infection vaccination statuses among the 3-5 years age groups (χ2 = 1.136, P = 0.286).

Conclusions

In children aged 0-17 years infected with SARS-CoV-2 Omicron variant, fever was the primary clinical manifestation in the acute phase, followed by respiratory symptoms, systemic non-specific and digestive presentations. In particular, respiratory and digestive system symptoms were more frequent in children aged above 6 years. Regarding the long-term symptoms from 4 to 12 weeks post-infection, the most common presentations were concentrating difficulty, cough, and fatigue. The incidence of persistent symptoms of SARS-CoV-2 did not exhibit a significant correlation with vaccination status, which was attributed to the waning efficacy of the vaccine-induced humoral immune response after 6 months.

The protective effects of pediatric vaccination on multisystem inflammatory syndrome in children stratified by vaccine status, types and virus variants

BACKGROUND

Few studies highlight the stratification of COVID-19 vaccine effectiveness on MIS-C according to vaccine status, types and SARS-COV-2 variants.

METHODS

A web-based analysis was conducted through searches of PubMed, Web of Science and Medline databases from January 1, 2020, to May 16, 2023. The search terms used were (multisystem inflammatory syndrome in children OR MIS-C OR PIMS OR PIMS-TS) AND (COVID-19 OR SARS-CoV-2) AND (vaccine OR vaccination) AND (children OR adolescents OR pediatric).

RESULTS

6701 children from 13 studies met the MIS-C definition. 92.1 % (1332/1446) of MIS-C cases were unvaccinated, whereas partial vaccination and full vaccination were 3.7 % (54/1446) and 4.2 % (60/1446)respectively. In the two studies encompassing 41 vaccinated MIS-C cases, 34 (82.9 %) received BNT162b2, 2 (4.9 %) received mRNA-1273, 4 (9.8 %) received Sinovac vaccine, and only one received a heterologous primary-boost regimen. Among 838 vaccinated MIS-C cases with different SARS-COV-2 variants, 23（2.8 %） were infected by the Wild-type, 80（9.5 %） by the Alpha variant, 521（62.2 %） by the Delta variant, and 214（25.5 %） by the Omicron variant. A significant difference was observed in vaccination rates among MIS-C cases across different variant pandemics (χ2 = 37.79, P < 0.001). The highest vaccination rate (26.3 %) occurred in the Alpha predominant period, thereafter dropped to 5.0 % in the Delta predominant period, and then increased to 12.6 % in the Omicron predominant period.

CONCLUSIONS

Heterologous vaccination might provide a slightly more protective effect than homologous manner for MIS-C. As the virus mutates over time, its pathogenicity to MIS-C degrades among vaccinated individuals.

Incidence of SARS-CoV-2 infection in children shortly after ending zero-COVID-19 policy in China on December 7, 2022: a cross-sectional, multicenter, seroepidemiological study

Background

China discontinued the zero-COVID-19 policy on December 7, 2022, and then COVID-19 surged mid-December 2022 through mid-January 2023. However, the actual incidence was unknown. This study aimed to estimate the incidence of SARS-CoV-2 infection in children shortly after ending the zero-COVID-19 policy.

Methods

This multicenter cross-sectional study included 1,065 children aged 8 months to 12 years from seven hospitals at six regions across Jiangsu province, based on the convenience sampling, from February 10 to March 10, 2023. Group I comprised 324 children aged 8 months-2 years without COVID-19 vaccination, group II consisted of 338 preschool children aged 3-5 years with varied vaccination history, and group III contained 403 primary school children aged 6-12 years with mostly vaccinated. The COVID-19 vaccines were composed of inactivated SARS-CoV-2. In addition, 96 children's sera collected in 2014 were included as negative controls. IgG and IgM antibodies against nucleocapsid (N) and subunit 1 of spike (S1) of SARS-CoV-2 (anti-N/S1) were measured with commercial kits (YHLO Biotech, Shenzhen, China).

Results

None of the 96 children (5.1 ± 3.5 years; 58.3% boys) in 2014 was positive for anti-N/S1 IgG or IgM. Of the 1,065 children (5.0 ± 3.5 years; 56.0% boys), 988 (92.8%) were anti-N/S1 IgG positive but none was anti-N/S1 IgM positive. The positive rate of anti-N/S1 IgG in Group I, II, and III was 90.4, 88.5, and 98.3%, respectively, with significantly higher in group III than in groups I and II (p < 0.0001). The median antibody titers in group III (381.61 AU/ml) were much higher than that in group I (38.34 AU/ml) and II (51.88 AU/ml; p < 0.0001).

Conclusion

More than 90% children experienced SARS-CoV-2 infection shortly after ending zero-COVID-19 policy in China, much higher than estimated infections by other studies. The widespread SARS-CoV-2 infection in unvaccinated children should be influential on the policy of COVID-19 vaccination in children in the future.

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.