Incidence, Risk, and Severity of SARS-CoV-2 Reinfections in Children and Adolescents Between March 2020 and July 2022 in Serbia

Risk of reinfection and severity with the predominant BA.5 Omicron subvariant China, from December 2022 to January 2023

Data on reinfection in large Asian populations are limited. In this study, we aimed to evaluate the reinfection rate, disease severity, and time interval between the infections in the symptomatic and asymptomatic populations which are firstl infected with BA.2 Omicron Variant. We retrospectively included adult patients with COVID-19 discharged from four designated hospitals between 27 April 2021 and 30 November 2022, who were interviewed via telephone from 29 January to 1 March 2023. Univariable and multivariable analyses were used to explore risk factors associated with reinfection. A total of 16,558 patients were followed up, during the telephone survey of an average of 310.0 days, 1610 (9.72%) participants self-reported reinfection. The mean time range of reinfection was 257.9 days. The risks for reinfection were analysed using multivariable logistic regression. Patients with severe first infection were at higher risk for reinfection (aORs, 2.50; P < 0.001). The male (aORs,0.82; P < 0.001), the elderly (aORs, 0.44; P < 0.001), and patients with full vaccination (aORs, 0.67; P < 0.001) or booster (aORs, 0.63; P < 0.001) had the lower risk of reinfection. Patients over 60 years of age (aORs,9.02; P = 0.006) and those with ≥2 comorbidities (aORs,11.51; P = 0.016). were at higher risk for severe reinfection. The number of clinical manifestations of reinfection increases in people with severe first infection (aORs, 2.82; P = 0.023). The overall reinfection rate was 9.72%, and the reinfection rate of Omicron-to-Omicron subvariants was 9.50% at one year. The severity of Omicron-Omicron reinfection decreased. Data from our clinical study may provide clinical evidence and bolster response preparedness for future COVID-19 reinfection waves.

SARS-CoV-2 Test-to-Stay in Daycare

BACKGROUND AND OBJECTIVES

Test-to-stay concepts apply serial testing of children in daycare after exposure to SARS-CoV-2 without use of quarantine. This study aims to assess the safety of a test-to-stay screening in daycare facilities.

METHODS

714 daycare facilities and approximately 50 000 children ≤6 years in Cologne, Germany participated in a SARS-CoV-2 Pool-polymerase chain reaction (PCR) screening from March 2021 to April 2022. The screening initially comprised post-exposure quarantine and was adapted to a test-to-stay approach during its course. To assess safety of the test-to-stay approach, we explored potential changes in frequencies of infections among children after the adaptation to the test-to-stay approach by applying regression discontinuity in time (RDiT) analyses. To this end, PCR-test data were linked with routinely collected data on reported infections in children and analyzed using ordinary least squares regressions.

RESULTS

219 885 Pool-PCRs and 352 305 Single-PCRs were performed. 6440 (2.93%) Pool-PCRs tested positive, and 17 208 infections in children were reported. We estimated that during a period of 30 weeks, the test-to-stay concept avoided between 7 and 20 days of quarantine per eligible daycare child. RDiT revealed a 26% reduction (Exp. Coef: 0.74, confidence interval 0.52-1.06) in infection frequency among children and indicated no significant increase attributable to the test-to-stay approach. This result was not sensitive to adjustments for 7-day incidence, season, SARS-CoV-2 variant, and socioeconomic status.

CONCLUSIONS

Our analyses provide evidence that suggest safety of the test-to-stay approach compared with quarantine measures. This approach offers a promising option to avoid use of quarantine after exposure to respiratory pathogens in daycare settings.

Effectiveness of COVID-19 vaccines among children 6-11 years against hospitalization during Omicron predominance in Malaysia

There is currently limited data on the effectiveness of COVID-19 vaccines for children aged 6-11 years in Malaysia. This study aims to determine vaccine effectiveness (VE) against COVID-19-related hospitalization after receipt of one- and two-doses of BNT162b2 mRNA (Comirnaty-Pfizer/BioNTech) vaccine over a duration of almost 1 year in the predominantly Omicron period of BA.4/BA.5 and X.B.B sub lineages. This study linked administrative databases between May 2022 and March 2023 to evaluate real-world vaccine effectiveness (VE) for the BNT162b2 mRNA (Comirnaty-Pfizer/BioNTech) vaccine against COVID-19-related hospitalization in the Omicron pre-dominant period with BA.4/BA.5 and X.B.B sub lineages. During the Omicron-predominant period, the cumulative hospitalization rate was almost two times higher for unvaccinated children (9.6 per million population) compared to vaccinated children (6 per million population). The estimated VE against COVID-19 hospitalization for one dose of BNT162b2 was 27% (95% CI - 1%, 47%) and 38% (95% CI 27%, 48%) for two doses. The estimated VE against hospitalization remained stable when stratified by time. VE for the first 90 days was estimated to be 45% (95% CI 33, 55%), followed by 47% (95% CI 34, 56%) between 90 and 180 days, and 36% (95% CI 22, 45%) between 180 and 360 days. Recent infection within 6 months does not appear to modify the impact of vaccination on the risk of hospitalization, subject to the caveat of potential underestimation. In our pediatric population, BNT162b2 provided moderate-non-diminishing protection against COVID-19 hospitalization over almost 1 year of Omicron predominance.

Increased breadth and neutralization of antibodies against SARS-CoV-2 variants after infection and vaccination: A serosurveillance study in pediatric patients of Southern Switzerland

Little information is available about the nature of the immune response in children after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection or vaccination. The aim of this study is to define the seroprevalence and the features of the antibody response in children of Southern Switzerland during the different waves of Coronavirus Disease 2019 (COVID-19) pandemic. By analyzing 756 sera collected from children aged 0 to 16 years admitted to the Institute of Pediatrics of Southern Switzerland during the prepandemic period (before March 2020) and the first four pandemic waves (between March 2020 and June 2022), we investigated binding titers, cross-reactivity, and neutralizing properties of the serum antibodies against SARS-CoV-2 variants. Seroprevalence varied from 6% during the first wave to 14% and 17% during the second and third waves, respectively, peaking at 39% during the fourth wave. The 96 seropositive cases were mostly asymptomatic (42.7%) or showed mild (20.8%) to moderate (32.3%) symptoms. Moderate symptoms and close contact with COVID-19-positive individuals were associated with a higher infection risk (P < 0.001). The antibody response was mainly driven by IgG directed to the receptor-binding domain (RBD) of Wuhan-1 SARS-CoV-2 Spike (S). Children infected in the first three waves produced antibodies with up to 11-fold and 5.5-fold reduction in binding and neutralizing titers, respectively, against different SARS-CoV-2 variants, including Beta, Delta, and Omicron BA.1, BA.2, and BA.5. Such reductions were less pronounced in children infected during the fourth wave, who showed the highest frequency and titers of neutralizing antibodies against the same variants. Compared to infection, vaccination with a Wuhan-1-based messenger RNA (mRNA) vaccine induced higher and heterogenous levels of antibodies cross-reacting to the different SARS-CoV-2 variants analyzed.   Conclusions: Despite the high burden of COVID-19 in Southern Switzerland, we observed an initial low seroprevalence of SARS-CoV-2 in children, which increased in the later waves. The antibody response was poor in the first three waves and improved in the fourth wave, when children produced higher levels of neutralizing antibodies after vaccination or infection with Delta and/or Omicron variants. What is Known: • Children were marginally affected by the initial SARS-CoV-2 variants. • The number of infected and hospitalized children increased after the appearance of the Omicron variants. What is New: • Seroprevalence of SARS-CoV-2 in children of Southern Switzerland increased overtime. • Children produced higher levels of neutralizing antibodies after vaccination or infection with Delta and/or Omicron variants in the fourth wave compared to children infected in the first three waves.

Protective effect of previous infection and vaccination against reinfection with BA.5 Omicron subvariant: a nationwide population-based study in Japan

Background

The Omicron variant of SARS-CoV-2 was reported to evade immunity derived from vaccination and previous infection. A better understanding of hybrid immunity informs effective infection control strategies. Since the reinfection risk was not well-assessed in East Asia, this study aims to evaluate the risk of infection with Omicron subvariant BA.5 among previously infected individuals in Japan.

Methods

All notified cases were extracted from the Japanese national COVID-19 surveillance database including 20,297,335 records up to 25 September 2022. Reinfection with BA.5 was defined as the infection notified during the BA.5 dominated period with any prior SARS-CoV-2 infection. The protective effect of prior infections against reinfections with BA.5 was estimated by applying a case-population design and the protective effect of vaccination was estimated by a multivariable Cox regression adjusting for age, sex, variants of prior infection, and the time since the last vaccination.

Findings

Among 19,830,548 SARS-CoV-2 first infections, 233,424 (1.2%) were reinfected with BA.5. The protective effect against BA.5 reinfection of prior infection with Wuhan strain was 46%, Alpha variant was 35%, Delta variant was 41%, and BA.1/BA.2 subvariant was 74%. The reduced risk of BA.5 reinfection by 7%, 33%, and 66% was associated with two, three, and four doses of vaccination, respectively, compared with one-dose vaccination.

Interpretation

The prior infections with Omicron subvariant BA.1/BA.2 protected BA.5 reinfection more than pre-Omicron variants. Increased frequency of vaccination led to more protection from reinfection with BA.5. Up-to-date vaccination may be encouraged to prevent future reinfection among the previously infected population.

Funding

None.

Severe Pediatric COVID-19 and Multisystem Inflammatory Syndrome in Children From Wild-type to Population Immunity: A Prospective Multicenter Cohort Study With Real-time Reporting

BACKGROUND

SARS-CoV-2 variant evolution and increasing immunity altered the impact of pediatric SARS-CoV-2 infection. Public health decision-making relies on accurate and timely reporting of clinical data.

METHODS

This international hospital-based multicenter, prospective cohort study with real-time reporting was active from March 2020 to December 2022. We evaluated longitudinal incident rates and risk factors for disease severity.

RESULTS

We included 564 hospitalized children with acute COVID-19 (n = 375) or multisystem inflammatory syndrome in children (n = 189) from the Netherlands, Curaçao and Surinam. In COVID-19, 134/375 patients (36%) needed supplemental oxygen therapy and 35 (9.3%) required intensive care treatment. Age above 12 years and preexisting pulmonary conditions were predictors for severe COVID-19. During omicron, hospitalized children had milder disease. During population immunity, the incidence rate of pediatric COVID-19 infection declined for older children but was stable for children below 1 year. The incidence rate of multisystem inflammatory syndrome in children was highest during the delta wave and has decreased rapidly since omicron emerged. Real-time reporting of our data impacted national pediatric SARS-CoV-2 vaccination- and booster-policies.

CONCLUSIONS

Our data supports the notion that similar to adults, prior immunity protects against severe sequelae of SARS-CoV-2 infections in children. Real-time reporting of accurate and high-quality data is feasible and impacts clinical and public health decision-making. The reporting framework of our consortium is readily accessible for future SARS-CoV-2 waves and other emerging infections.

Persistent humoral immune response in youth throughout the COVID-19 pandemic: prospective school-based cohort study

Understanding the development of humoral immune responses of children and adolescents to SARS-CoV-2 is essential for designing effective public health measures. Here we examine the changes of humoral immune response in school-aged children and adolescents during the COVID-19 pandemic (June 2020 to July 2022), with a specific interest in the Omicron variant (beginning of 2022). In our study "Ciao Corona", we assess in each of the five testing rounds between 1874 and 2500 children and adolescents from 55 schools in the canton of Zurich with a particular focus on a longitudinal cohort (n=751). By July 2022, 96.9% (95% credible interval 95.3-98.1%) of children and adolescents have SARS-CoV-2 anti-spike IgG (S-IgG) antibodies. Those with hybrid immunity or vaccination have higher S-IgG titres and stronger neutralising responses against Wildtype, Delta and Omicron BA.1 variants compared to those infected but unvaccinated. S-IgG persist over 18 months in 93% of children and adolescents. During the study period one adolescent was hospitalised for less than 24 hours possibly related to an acute SARS-CoV-2 infection. These findings show that the Omicron wave and the rollout of vaccines boosted S-IgG titres and neutralising capacity. Trial registration number: NCT04448717. https://clinicaltrials.gov/ct2/show/NCT04448717 .

Epidemiological Characteristics of COVID-19 during Seven Consecutive Epidemiological Waves (2020-2022) in the North Bačka District, Serbia

The COVID-19 pandemic continues to pose a threat to global public health. The purpose of this research was to determine the epidemiological characteristics of COVID-19 in the North Bačka district while observing seven pandemic waves. The cross-sectional study was based on data from the COVID-19 surveillance database of the Institute for Public Health of Vojvodina during the period from March 2020 to December 2022. A total of 38,685 primary infections and 4067 reinfections caused by SARS-CoV-2 were notified. Pandemic waves caused by the Delta variant (cumulative incidence rate of 2482.37/100,000) and by the Omicron variant (cumulative incidence rate of 2994.45/100,000) emerged as significant focal points during the surveillance period. Over the course of three consecutive years (2020-2022), women were more affected (50.11%, 54.03%, and 55.68%, respectively). The highest incidence rates in age-specific categories were recorded in 2021 for the age group 40-49 (1345.32 per 10,000 inhabitants), while in 2022, they shifted towards the elderly population. Regarding vaccination status at the time of diagnosis, in 2021, around 15% of patients were vaccinated, while in 2022, the number increased to 37%. The most widely received vaccine was BBIBP-CorV (67.45%), followed by BNT162b2 (19.81%), Gam-COVID-Vac (9.31%), and ChAdOx1 nCoV-19 (3.42%) vaccine. The implementation of stringent public health measures and their mitigation, together with the emergence of new variants, influenced the dynamics of COVID-19 pandemic waves in the North Bačka district. Notably, throughout the study period, the working-age population was the most affected, along with females, with a mild clinical presentation dominating. Reinfections were most frequently recorded during the latter pandemic waves. Dealing with this pandemic has provided some valuable lessons for the development of future strategies in the case of a similar public health crisis.

International Pediatric COVID-19 Severity Over the Course of the Pandemic

Importance

Multiple SARS-CoV-2 variants have emerged over the COVID-19 pandemic. The implications for COVID-19 severity in children worldwide are unclear.

Objective

To determine whether the dominant circulating SARS-CoV-2 variants of concern (VOCs) were associated with differences in COVID-19 severity among hospitalized children.

Design, Setting, and Participants

Clinical data from hospitalized children and adolescents (younger than 18 years) who were SARS-CoV-2 positive were obtained from 9 countries (Australia, Brazil, Italy, Portugal, South Africa, Switzerland, Thailand, UK, and the US) during 3 different time frames. Time frames 1 (T1), 2 (T2), and 3 (T3) were defined to represent periods of dominance by the ancestral virus, pre-Omicron VOCs, and Omicron, respectively. Age groups for analysis were younger than 6 months, 6 months to younger than 5 years, and 5 to younger than 18 years. Children with an incidental positive test result for SARS-CoV-2 were excluded.

Exposures

SARS-CoV-2 hospitalization during the stipulated time frame.

Main Outcomes and Measures

The severity of disease was assessed by admission to intensive care unit (ICU), the need for ventilatory support, or oxygen therapy.

Results

Among 31 785 hospitalized children and adolescents, the median age was 4 (IQR 1-12) years and 16 639 were male (52.3%). In children younger than 5 years, across successive SARS-CoV-2 waves, there was a reduction in ICU admission (T3 vs T1: risk ratio [RR], 0.56; 95% CI, 0.42-0.75 [younger than 6 months]; RR, 0.61, 95% CI; 0.47-0.79 [6 months to younger than 5 years]), but not ventilatory support or oxygen therapy. In contrast, ICU admission (T3 vs T1: RR, 0.39, 95% CI, 0.32-0.48), ventilatory support (T3 vs T1: RR, 0.37; 95% CI, 0.27-0.51), and oxygen therapy (T3 vs T1: RR, 0.47; 95% CI, 0.32-0.70) decreased across SARS-CoV-2 waves in children 5 years to younger than 18 years old. The results were consistent when data were restricted to unvaccinated children.

Conclusions and Relevance

This study provides valuable insights into the impact of SARS-CoV-2 VOCs on the severity of COVID-19 in hospitalized children across different age groups and countries, suggesting that while ICU admissions decreased across the pandemic in all age groups, ventilatory and oxygen support generally did not decrease over time in children aged younger than 5 years. These findings highlight the importance of considering different pediatric age groups when assessing disease severity in COVID-19.

SARS-CoV-2 Reinfections and Long COVID in the Post-Omicron Phase of the Pandemic

We are reviewing the current state of knowledge on the virological and immunological correlates of long COVID, focusing on recent evidence for the possible association between the increasing number of SARS-CoV-2 reinfections and the parallel pandemic of long COVID. The severity of reinfections largely depends on the severity of the initial episode; in turn, this is determined both by a combination of genetic factors, particularly related to the innate immune response, and by the pathogenicity of the specific variant, especially its ability to infect and induce syncytia formation at the lower respiratory tract. The cumulative risk of long COVID as well as of various cardiac, pulmonary, or neurological complications increases proportionally to the number of SARS-CoV-2 infections, primarily in the elderly. Therefore, the number of long COVID cases is expected to remain high in the future. Reinfections apparently increase the likelihood of long COVID, but less so if they are mild or asymptomatic as in children and adolescents. Strategies to prevent SARS-CoV-2 reinfections are urgently needed, primarily among older adults who have a higher burden of comorbidities. Follow-up studies using an established case definition and precise diagnostic criteria of long COVID in people with or without reinfection may further elucidate the contribution of SARS-CoV-2 reinfections to the long COVID burden. Although accumulating evidence supports vaccination, both before and after the SARS-CoV-2 infection, as a preventive strategy to reduce the risk of long COVID, more robust comparative observational studies, including randomized trials, are needed to provide conclusive evidence of the effectiveness of vaccination in preventing or mitigating long COVID in all age groups. Thankfully, answers not only on the prevention, but also on treatment options and rates of recovery from long COVID are gradually starting to emerge.

Changing patterns of infectious diseases in children during the COVID-19 pandemic

Each infectious disease has had its own epidemic pattern and seasonality for decades. However, public health mitigation measures during the coronavirus disease 2019 (COVID-19) pandemic have resulted in changing epidemic patterns of infectious diseases. Stringent measures resulted in low incidences of various infectious diseases during the outbreak of COVID-19, including influenza, respiratory syncytial virus, pneumococcus, enterovirus, and parainfluenza. Owing to the prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections and subsequent immunity development, decreasing virulence of SARS-CoV-2, and worldwide immunization against SARS-CoV-2 in children beyond 6 months of age, mitigation measures are lifted country by country. Consequently, the immunity debt to infectious respiratory viruses other than SARS-CoV-2 contributed to the "off-season," "see-saw," and "upsurge" patterns of various infectious diseases in children. Moreover, apart from the persistence of SARS-CoV-2, the coexistence of other circulating viruses or bacterial outbreaks may lead to twindemics or tripledemics during the following years. Therefore, it is necessary to maintain hand hygiene and immunization policies against various pathogens to alleviate the ongoing impact of infectious diseases on children.