Seroprevalence of anti-SARS-CoV-2 antibodies and associated factors among household contacts of COVID-19 confirmed cases in Bangkok, Thailand

Factors influencing the time to COVID-19 antigen tests negative conversion among students at a Chinese university: a retrospective analysis

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can cause repeated infections. China experienced an outbreak of COVID-19 (coronavirus disease 2019) after the Chinese government changed its COVID-19 policy in December 2022. However, little is known about the influencing factors, such as a history of previous infection and vaccine dose, and whether these factors affect the time at which the antigen test results become negative for SARS-CoV-2. Boarding colleges and universities are prone to outbreaks caused by COVID-19. Therefore, we investigated the factors influencing the time of COVID-19 antigen tests conversion at one university from April to June 2023.

METHODS

This study included college students from one university in Guangzhou who tested positive for the COVID-19 antigen and collected information such as sex, history of previous COVID-19 infection, vaccination dose, symptom onset date, and antigen tests conversion date for retrospective analysis. Chi-square tests or t-tests were used to compare differences between groups.

RESULTS

A total of 255 college students were included in this study. In addition to fever, the most common symptoms were sore throat, nasal symptoms and fatigue. The average time to antigen tests negative conversion of patients with their first infection was 6.12 ± 1.83 days, and that of patients with their second infection was 4.70 ± 1.43 days. The difference between the groups was statistically significant (P < 0.001). The average time to antigen tests negative conversion was 6.21 ± 1.92 days in patients with more than 3 symptoms except fever, which was significantly greater than that in patients with 0-1 (5.54 ± 1.79 days) or 2-3 symptoms (5.45 ± 1.78 days) (P < 0.05). There was no significant difference in time to antigen tests negative conversion according to sex, health observation location or vaccination dose (P > 0.05).

CONCLUSION

In college students, a history of SARS-CoV-2 infection as well as the number of symptoms were significantly associated with the time to COVID-19 antigen tests conversion.

Seroprevalence of SARS-CoV-2 infection in pediatric patients in a tertiary care hospital setting

Globally, cases of children's coronavirus disease 2019 (COVID-19) have been reported since the pandemic started. Most children have an asymptomatic or mild infection. Therefore, the incidence rate of COVID-19 in children might have been underestimated. This study aimed to determine (1) the seroprevalence (and seroconversion rates) of COVID-19, including associated risk factors, in pediatric patients visiting hospitals; and (2) the immunological responses to COVID-19. This was a prospective, cross-sectional study. Patients aged 0-18 years who visited the hospital from September 2020 to February 2022 were included. Demographic, clinical, and laboratory data were reviewed. A total of 1,443 pediatric patients were enrolled. Of these, 323 (22.6%) had a history of COVID-19. In the pre-Delta period, the seroprevalence increased from 4.1% to 70.6% in all included patients and from 0.5% to 10% in patients without a known history of COVID-19 compared with the Delta-Omicron period. The seroconversion rate was 6.8% (19 per 100 person-years) in pediatric patients with COVID-19. Risk factors for COVID-19 seropositivity were respiratory symptoms, being in an outpatient department setting, and infection during the Delta-Omicron period. Exposure to household members with confirmed COVID-19 was a risk factor for seropositivity and seroconversion. Infection during the Delta-Omicron period and testing conducted >2 weeks after the onset of symptoms was associated with spike immunoglobulin (Ig) M and spike and nucleocapsid IgG, respectively. High nucleocapsid IgG levels were associated with pneumonia in pediatric patients with COVID-19. Pediatric patients exposed to household members with COVID-19 and respiratory symptoms should be tested for COVID-19. Nucleocapsid IgG can be used as a surrogate marker to identify patients who may have experienced pneumonia from COVID-19 and as a screening tool for the COVID-19 outbreak, regardless of COVID-19 vaccination status.

Seroprevalence of SARS-CoV-2 nucleocapsid antibody among sex workers during the 5th epidemic wave with Omicron variant in Chiang Mai, Thailand

Objectives

To investigate the seroprevalence of SARS-CoV-2 nucleocapsid antibodies (NC-Ab) in sex workers.

Methods

A cross-sectional/observational study was conducted between March and December 2022 among sex workers living in Chiangmai, Thailand, aged over 18 years and who had engaged in sex work in the previous 12 months. Consenting individuals completed a questionnaire and had blood drawn. IgG-specific for SARS-CoV-2 nucleocapsid was assessed using Euroimmun anti-SARS-CoV-2 NCP ELISA (IgG).

Results

264 sex workers (52.3 % male) with a median age 31 years were included. The overall seroprevalence of SARS-CoV-2 NC-Ab was 42.4 % (44.2 % in males, 40.5 % in females). It was significantly higher among non-Thai than Thai sex workers (57.1 % vs. 37.1 %, p = 0.004) and among individuals who reported a history of COVID-19 as compared those who did not (54.9 % vs. 34.3 %, p = 0.036). NC-Ab seroprevalence did not differ by sex, age, receipt of COVID-19 vaccines, or the number of vaccine doses. SARS-CoV-2 NC-Ab seropositivity was significantly associated with being non-Thai, having monthly income >15,000 Baht, having received inactivated COVID-19 vaccines, and having been diagnosed with COVID-19.

Conclusions

This study shows a high seroprevalence of NC-Ab among sex workers in Chiangmai, Thailand during the fifth epidemic wave with Omicron variant. This may be due to combined effects of high transmissibility of the Omicron variant and high-risk behavior of those individuals. Specific health education interventions are needed for this specific population.

Association between COVID-19 Vaccination and SARS-CoV-2 Infection among Household Contacts of Infected Individuals: A Prospective Household Study in England

BACKGROUND

We investigated whether COVID-19 vaccination reduced SARS-CoV-2 infection risk among adult household contacts of COVID-19 index cases during the Alpha, Delta, and Omicron waves in England.

METHODS

Between February 2021 and February 2022, SARS-CoV-2 RT-PCR nasal swabs were collected from COVID-19-confirmed index cases aged ≥20 years and their household contacts at enrolment and three and seven days thereafter. Generalized Estimating Equations models were fitted with SARS-CoV-2 positivity as the outcome and household contacts' vaccination status as the main exposure while adjusting for confounders.

RESULTS

SARS-CoV-2 infection was confirmed in 238/472 household contacts (50.4%) aged ≥20 years. The adjusted relative risk (95% confidence interval) of infection in vaccinated versus unvaccinated household contacts was 0.50 (0.35-0.72) and 0.69 (0.53-0.90) for receipt of two doses 8-90 and >90 days ago, respectively, and 0.34 (0.23-0.50) for vaccination with three doses 8-151 days ago. Primary vaccination protected household contacts against infection during the Alpha and Delta waves, but only three doses protected during the Omicron wave. Vaccination with three doses in the index case independently reduced contacts' infection risk: 0.45 (0.23-0.89).

CONCLUSIONS

Vaccination of household contacts reduces their risk of infection under conditions of household exposure though, for Omicron, only after a booster dose.