Background: Although inactivated COVID-19 vaccines are proven to be safe and effective in the general population, the dynamic response and duration of antibodies after vaccination in the real world should be further assessed.Methods: We enrolled 1067 volunteers who had been vaccinated with one or two doses of CoronaVac in Zhejiang Province, China. Another 90 healthy adults without previous vaccinations were recruited and vaccinated with three doses of CoronaVac, 28 days and 6 months apart. Serum samples were collected from multiple timepoints and analyzed for specific IgM/IgG and neutralizing antibodies (NAbs) for immunogenicity evaluation. Antibody responses to the Delta and Omicron variants were measured by pseudovirus-based neutralization tests.Results: Our results revealed that binding antibody IgM peaked 14–28 days after one dose of CoronaVac, while IgG and NAbs peaked approximately 1 month after the second dose then declined slightly over time. Antibody responses had waned by month 6 after vaccination and became undetectable in the majority of individuals at 12 months. Levels of NAbs to live SARS-CoV-2 were correlated with anti-SARS-CoV-2 IgG and NAbs to pseudovirus, but not IgM. Homologous booster around 6 months after primary vaccination activated anamnestic immunity and raised NAbs 25.5-fold. The neutralized fraction subsequently rose to 36.0% for Delta (p=0.03) and 4.3% for Omicron (p=0.004), and the response rate for Omicron rose from 7.9% (7/89)–17.8% (16/90).Conclusions: Two doses of CoronaVac vaccine resulted in limited protection over a short duration. The inactivated vaccine booster can reverse the decrease of antibody levels to prime strain, but it does not elicit potent neutralization against Omicron; therefore, the optimization of booster procedures is vital.Funding: Key Research and Development Program of Zhejiang Province; Key Program of Health Commission of Zhejiang Province/ Science Foundation of National Health Commission; Major Program of Zhejiang Municipal Natural Science Foundation; Explorer Program of Zhejiang Municipal Natural Science Foundation.

Respiratory syncytial virus (RSV) is an important pathogen that causes acute respiratory tract infections in children. To understand the epidemiological and clinical characteristics of RSV in children, we analyzed the RSV diagnostic testing results from the 2014–2018 surveillance of acute respiratory infections in China. Among children aged <5 years, RSV incidence during 2014–2018 was 17.3% (3449/19,898), and 89.1% of RSV-positive individuals were inpatients. Children aged < 6 months had a high proportion in RSV infected individual (n = 1234; 35.8%). The highest RSV detection rate was in winter, RSV-A and RSV-B co-circulated year-round and jointly prevailed in 2015–2016. Cough was the common symptom of RSV infection 93.2% (3216/3449). Compared with older children, those aged <6 months were more likely to show breathing difficulty or lung rale that further developed into bronchopneumonia (p < 0.001). The symptoms such as cough, running nose, and diarrhea had significant differences between the RSV-A and RSV-B groups. The rate of RSV co-detection with other viruses or bacteria was 35.4%. Those coinfected with other viruses had a significantly higher incidence of fever, whereas those coinfected with bacteria had higher incidences of breathing difficulty and severe pneumonia. Our findings highlight the need for accumulating epidemiological information for the prevention and control of RSV.

Background: The resurgence of pertussis has emerged as a significant global public health threat. Severe pertussis primarily affects infants and children and is often associated with serious complications or death. Methods: We retrospectively evaluated the clinical data of 197 hospitalized children with pertussis admitted to Children’s Hospital, Zhejiang University School of Medicine, from 2019 to 2024. Patients were categorized into severe and mild cases groups based on their admission ward. Multivariate logistic model was applied to explore associated factors. Results: Among the 197 hospitalized children, those born prematurely or younger than 3 months were more likely to be admitted to the pediatric intensive care unit (PICU). All patients admitted to the PICU were infants who were either unvaccinated or incompletely vaccinated against pertussis. The most common clinical symptoms among hospitalized children were pneumonia, paroxysmal cough, and flushing. The severe cases group exhibited significantly higher levels than the mild cases group in length of stay, duration of antibiotic treatment, white blood cell (WBC) count, pneumonia, respiratory failure, and tachypnea ( p < 0.05). Multivariate logistic regression analysis identified cefuroxime usage [odds ratio (OR) = 0.10, 95% confidence interval (CI) = 0.01–0.92], high WBC count (OR = 0.79, 95% CI = 0.69–0.91), and high neutrophil percentage (OR = 1.49, 95% CI = 1.22–1.82) as independent risk factors for PICU admission ( p < 0.05). Conclusion: Infants younger than 3 months and children who are unvaccinated or incompletely vaccinated for pertussis are more susceptible to developing severe pertussis. Common clinical features of severe pertussis include pneumonia, respiratory failure, elevated WBC count, and decreased neutrophil percentage. Pediatricians should prioritize early recognition and treatment of these clinical indicators to prevent the progression of severe pertussis.

Seasonal influenza vaccination is highly recommended for 6–59-month-old children. To determine the impact of seasonal influenza and the factors affecting influenza vaccine uptake among children, we conducted an opt-in Internet panel survey of parents from 21 March 2018 to 1 April 2018. Overall, 40.5% (1913/4719) of children experienced influenza-like illness (ILI), 92.4% of parents sought medical care for children with ILI (outpatients: 61.2%, inpatients: 12.8%), 39.6% of parents preferred to take their sick child to a tertiary hospital, and 57.3% of family members requested leave to care for children with ILI. There was a median of three days of absenteeism (2, 5) per sick child, and 39.4% of children received the influenza vaccine during the 2017–2018 influenza season. Vaccine coverage among children aged 6–11 months and 48–59 months was lower than that among 12–47-month-old children. The top three reasons for not vaccinating were: the influenza vaccine was not recommended by healthcare workers (21.1%), no knowledge about the influenza vaccine (19.2%), and lack of confidence in the vaccine’s effectiveness (14.3%). Our findings highlight the need for awareness about the severity of influenza, hygiene behavior, and effectiveness of the influenza vaccine among children and their family members in China.

Zika virus (ZIKV)-specific T cells are activated by different peptides derived from virus structural and nonstructural proteins, and contributed to the viral clearance or protective immunity. Herein, we have depicted the profile of CD8+ and CD4+ T cell immunogenicity of ZIKV proteins in C57BL/6 (H-2^b) and BALB/c (H-2^d) mice, and found that featured cellular immunity antigens were variant among different murine alleles. In H-2^b mice, the proteins E, NS2, NS3 and NS5 are recognized as immunodominant antigens by CD8+ T cells, while NS4 is dominantly recognized by CD4+ T cells. In contrast, in H-2^d mice, NS1 and NS4 are the dominant CD8+ T cell antigen and NS4 as the dominant CD4+ T cell antigen, respectively. Among the synthesized 364 overlapping polypeptides spanning the whole proteome of ZIKV, we mapped 91 and 39 polypeptides which can induce ZIKV-specific T cell responses in H-2^b and H-2^d mice, respectively. Through the identification of CD8+ T cell epitopes, we found that immunodominant regions E_294-302 and NS4_2351-2360 are hotspots epitopes with a distinct immunodominance hierarchy present in H-2^b and H-2^d mice, respectively. Our data characterized an overall landscape of the immunogenic spectrum of the ZIKV polyprotein, and provide useful insight into the vaccine development.