The previous study reported that significantly decreased infection fatality rates associated with SARS-CoV-2 Omicron infection in children and young people in England [1]. The majority of children appear to have asymptomatic, mild, or moderate disease of Omicron infection [2, 3]. However, there are limited data about Omicron infection in children in China. Here, we evaluated the infection fatality rates, clinical features and efficacy of SARS-CoV-2 vaccine in children with Omicron infection in a tertiary hospital during the first wave of SARS-CoV-2 caused by Omicron in China, December 2022-January 2023.
The Chinese government's New 10 epidemic prevention strategy, which was unveiled on December 7, 2022, stated that the dynamic zero-COVID policy, which had been implemented for around three years, was moving toward reopening. The pandemic spread quickly over the next two months, as expected, in the face of the highly contagious omicron subvariants BA.5.2 and BF.7 [4]. In this wave of the epidemic, we retrospectively analyzed patients with omicron infection aged 0-14 years in a tertiary hospital in Hangzhou. Data on general features, initial symptoms, laboratory tests and outcomes were retrieved from electronic medical records. Continuous variables were represented by the median and interquartile range (IQR), whereas categorical variables were represented by counts and percentages. Pearson's chi-squared test or Fisher's exact test was performed to compare differences in proportions of categorical variables. The Mann-Whitney U test was performed to analyse the differences between the two groups of independent continuous variables. When judging the level of significance, a difference of P<0.05 was considered statistically significant.
From December 1, 2022 to January 31, 2023, a total of 44,045 individuals were tested for COVID-19 using pharyngeal swab specimens and a real-time RT-PCR assay at Zhejiang Provincial People's Hospital in Hangzhou, China. Table S1 shows their demographic information. Among them, 23.9% (10515/44045) were laboratory-confirmed as COVID-19 nucleic acid testing (NAT) positive. The median age of NAT-positive patients was 42 years (IQR, 27-69), with males accounting for 53.3% (5607/10515).
We used the week as a statistical unit, and the positive rate of NAT was 0.03% from December 1 to December 7, the week before the Zero-COVID strategy was relaxed. Following the repeal of the Zero-COVID policy, the positive rate of NAT rose to 8.3% in the first week, peaked at 85.2% in the third week, and then steadily fell (Figure 1A). According to the daily monitoring, the highest daily NAT positive rate was 94.5% on December 24, 2022, the 17th day after the Zero-COVID policy was terminated (Figure 1B). Individuals were further divided into three age groups (0-14, 15-59, and ≥60). The group ≥60 years old had the highest NAT positive rate (39.5%) (Table S1). Children (0-14 years) accounted for 1691, with an overall NAT positive rate of 37.9% (641/1691). The NAT positive rate in children peaked (90.4%) in the third week following the termination of the Zero-COVID policy (Figure 1C). Daily monitoring revealed that the NAT positive rate of children peaked (95.0%) on the 17th day after the termination of the Zero-COVID policy (December 24, 2022), at the same time as the population peaked (Figure 1D). 532 of the 641 pediatric patients who tested positive for NAT were seen in the pediatric outpatient clinic. Eventually, 51 pediatric patients were admitted to hospitals.There were no fatalities among these pediatric patients.
We analyzed the pediatric patients' initial symptoms as well as their vaccination status (Figure 2). The majority of children with infection had upper respiratory symptoms, with 97.4% (518/532) having fever, 65.0% (346/532) having cough, 33.6% (179/532) having runny nose, 28.8% (153/532) having stuffy nose, and 20.7% (110/532) having sputum production. Some children experienced digestive issues such as vomiting and diarrhea. Twelve (2.3%) of the children were severe illness and exhibited with febrile convulsions. 43.6% (232/532) of the 532 pediatric patients received vaccinations, with the majority (95.3%, 221/232) receiving two doses and the remainder receiving one (Table S2). Of the 12 children with severe illnesses, ten had not had a vaccination, whereas the other two had. Children who were unvaccinated experienced a severe illness rate of 3.33% (10/300) whereas those who were vaccinated saw a rate of 0.86% (2/232). The rate of severe illness in the unvaccinated group of children was significantly higher than in the vaccinated group. According to data on febrile patients' temperatures, the proportion of children with high temperatures (≥39℃) was lower in the vaccinated group than in the unvaccinated group (43.3% vs 54.6%). Table S3 displays the statistical findings of a peripheral blood cell study done on 490 pediatric patients. Leucopenia was found in 9.1% (46/490) of the children, while lymphopenia was seen in 32.6% (159/490). Elevated peripheral blood monocyte count was seen in 61.4% (299/490) of children. At the time of their initial diagnosis, 19.9% (97/490) of pediatric patients had an increased CRP.
The COVID-19 pandemic has been ongoing for over three years, with the emergence of variants such as alpha, beta, gamma, delta, and omicron resulting in multiple waves around the world [5, 6]. Since omicron emergent, it rapidly became dominant worldwide [7]. Numerous studies have found that infection with the omicron variant had different clinical patterns and was associated with better outcomes than the prior variant [8-10]. With the end of the dynamic COVID-zero strategy, people in China were pulled through the first wave of SARS-CoV-2 caused by omicron in the year-end of 2022. The clinical symptoms in children during this wave of omicron infection were mainly fever, cough, and raised peripheral blood mononuclear cell counts. Overall, the symptoms of infection were mild, and the rate of severe disease was low, whereas vaccination had a favorable effect on lowering the risk of severe illness in children.