Effect of Vaccination on Household Transmission of SARS-CoV-2

Background. Understanding how COVID-19 vaccination affects transmission of SARS-CoV-2 within households may affect policy and healthcare decisions. We hypothesized that vaccination reduces transmission and viral load in vaccinated household members. Methods. We prospectively enrolled participants during March 2020 - October 2021. Index cases (IC) were eligible if they tested positive for SARS-CoV-2 within the previous 10 days and did not have household contacts (HC) who had tested positive or had symptoms of COVID-19. Participants self-collected anterior nares swabs daily for SARS-CoV-2 RT-PCR for at least 21 days, or once every member of the household had 7 consecutive negative tests. Baseline data included demographics and self-reported vaccination status. Complete COVID-19 vaccination was defined as receiving 2 doses of Moderna/Pfizer or 1 dose of Johnson & Johnson vaccine, and incomplete vaccination as receiving 1 dose of Moderna/Pfizer vaccine. Household transmission was analyzed via STATA 14.2 using logistic regression with robust standard error clustered by household, and SARS-CoV-2 cycle threshold was graphed by day of study enrollment using lowess smoothing. Results. There were 60 households with positive ICs and 103 HCs for a total of 163 participants. ICs had median age 41.5 years (range 1-86) with 9 (18.0%) < 18 years. HCs had median age 34 years (range 0-87) with 32 (31.1%) HCs < 18 years. Overall, 33 (20.2%) participants received at least one COVID-19 vaccine dose. A total of 50 households had at least one HC (median 2, max 7). Transmission of SARS-CoV-2 occurred in 45 HCs (43.7%). Odds of SARS-CoV-2 transmission was lower in HCs who were vaccinated prior to study enrollment, though this finding was not statistically significant (Table 1). There were 507 positive SARS-CoV-2 tests collected among 74 participants (Figure 1). Completely vaccinated: Received primary COVID-19 vaccination series (2 doses Pfizer or Moderna vaccine, or 1 dose Johnson & Johnson vaccine) prior to enrollment Conclusion. Vaccination of HCs may be protective against household SARS-CoV-2 transmission. However, analyses were limited due to low numbers of vaccinated study participants. Study enrollment is ongoing, and future analyses will include transmission during the 2022 Omicron surge, and daily symptom data which has been collected.

Duration of Seroprevalence among Individuals Previously Infected with SARS-CoV-2 and their Household Contacts

Background. Serological tests directed against SARS-CoV-2 can provide information about the timing of infection and immunity against the virus. However, the kinetics of the host immune response to SARS-CoV-2 remain poorly understood. We established a household transmission study to analyze the serological responses within households, to determine longitudinal immune responses to infection. Methods. From April 2020 to April 2022, we prospectively enrolled 76 households with at least one RT-PCR confirmed case of COVID-19. Participants were asked to provide blood samples at three time points: at baseline within 2 weeks of the index's diagnosis of COVID-19, and at one- and three-months post-enrollment. Samples were tested for the presence of IgG antibodies against SARS-CoV-2 spike protein via an FDA EUA approved ELISA. Demographics, medical history, and symptomatology were also collected. Results. To date, we have analyzed 238 serologic samples from 135 participants, including 82 baseline samples, 89 one-month samples, and 67 three-month samples. At baseline, 67.8% (n=40/59) of all confirmed cases tested positive for SARS-CoV-2 antibodies, which increased to 86.4% (n=57/66) at the one month, and 85.1% at three months (n=40/47). Of those confirmed infected participants that failed to seroconvert at baseline, almost all reported symptoms (n=14/19, 73.7%) and did not have chronic medical conditions (n=17/19, 89.5%). Of the 19, 3 failed to seroconvert by their third visit. All individuals who were fully vaccinated at the time of each visit tested positive for antibodies at baseline (n=26), one-month (n=27), and three-months (n=20). Of those who were not fully vaccinated, 56 (41.1%) were positive for antibodies at baseline, 62 (59.7%) were positive at one -month, and 47 (63.8%) at three-months. Differences in seropositivity rates between pediatric and adult participants, as well as between index cases and household contacts, at each visit were also identified (Table 1). Conclusion. Identifying differences in seroprevalence in various demographic groups can provide insight into longitudinal immune responses post-infection. Future analyses on seropositivity among previously infected individuals who received therapeutics may be of interest.

Breath Sample Collection from Individuals Infected with SARS-CoV-2: Biosafety Methodology

Background. Breath samples collected from patients infected with respiratory viruses are necessary for viral detection using breath analyzer devices. Given the highly transmissible nature of many of these illnesses, sample collection requires a multilayered approach to ensure the safety of the research staff responsible for obtaining and transporting these samples. Our team established a protocol to minimize exposure to and transmission of COVID-19 when collecting breath samples. Methods. We collected breath samples from 64 participants, of which 31 (48.4%) were positive for SARS-CoV-2 at the time of their visit. Before we started sample collection, biosafety inspection was conducted. We used a five-pronged approach to enhance safety and minimize transmission. First, we collected specimens in an outdoor space while the patients were seated in their vehicles. Second, we used a disposable mouthpiece and a one-way valve tofill a 1L TEDLAR bag. Third, patients were instructed to close the valve tightly before returning it to the staff. Fourth, we placed the bag in secondary containers which were placed in tertiary containers to minimize any contact with aerosols in the TEDLAR bag. In the last step, we placed a portable HEPAfilter near the indoor sample processing unit to minimize exposure and air contamination with the samples. Study staff donned all forms of necessary personal protective equipment, including gloves, gowns, N95 respirators, and protective eyewear, during sample collection and transportation. Results. A total of 64 breath samples were collected from 64 adult participants from February to March 2022. A total of 30 participants (46.9%) were within 7 days of their initial diagnosis. All participants were able to successfully collect samples without additional resources or attempts. All samples were able to be transported successfully into the lab. No staff contracted COVID-19 during the study period. Conclusion. Layered safety measures, including protective equipment, physical barriers, and well-ventilated environments mitigated the risks associated with breath sample collections from infected participants.

Feasibility of Specimen Self-collection in Young Children Undergoing SARSCoV-2 Surveillance for In-person Learning

Background. While pediatric cases of COVID-19 are at low risk for adverse events, schoolchildren should be considered for surveillance as they can become infected at school and serve as sources of household or community transmission. Our team assessed the feasibility of young children self-collecting SARS-CoV-2 samples for surveillance testing in an educational setting. Methods. Students at a K-8 school were tested weekly for SARS-CoV-2 from September 2020 - June 2021. Error rates were collected from September 2020 -January 2021. Clinical staff provided all students with instructions for anterior nares specimen self-collection and then observed them to ensure proper technique. Instructions included holding the sterile swab while making sure not to touch the tip, inserting the swab into their nostril until they start to feel resistance, and rubbing the swab in four circles before repeating the process in their other nostril. An independent observer timed random sample self-collections from April - June 2021. Results. 2,590 samples were collected from 209 students during the study period when data on error rates were collected. Errors occurred in 3.3% of all student encounters (n=87). Error rates over time are shown in Figure 1, with the highest rate occurring on the first day of testing (n=20/197, 10.2%) and the lowest in January 2021 (n=1/202, 0.5%). 2,574 visits for sample self-collection occurred during the study period when independent timing data was collected (April - June 2021). Of those visits, 7.5% (n=193) were timed. The average duration of each visit was 70 seconds. Conclusion. Pediatric self-collected lower nasal swabs are a viable and easily tolerated specimen collection method for SARS-CoV-2 surveillance in school settings, as evidenced by the low error rate and short time window of sample self-collection during testing. School administrators should expect errors to drop quickly after implementing testing.

Natural History of Shedding and Household Transmission of Severe Acute Respiratory Syndrome Coronavirus 2 Using Intensive High-Resolution Sampling

Background. In order to mitigate the spread of SARS-CoV-2 and the COVID-19 pandemic, public health officials have recommended self-isolation, self-quarantine of exposed household contacts (HHC), and mask use to limit viral spread within households and communities. While household transmission of SARS-CoV-2 is common, risk factors for HHC transmission are poorly understood. Methods. In this prospective cohort study, we enrolled 37 households with at least one reverse transcription polymerase chain reaction-confirmed (RT-PCR) COVID-19 index case from March 2020 - March 2021, in order to calculate secondary attack rates (SAR) and define risk factors for secondary infections. Participants were tested daily for SARS-CoV-2 via RT-PCR, using self-collected lower nasal samples. Households were followed until all members tested negative for seven consecutive days. We collected demographics, medical conditions, relationship to index case, and socioeconomic indicators. Subgroup data analysis was conducted and stratified by positivity status. Results. Of 99 enrolled participants, 37 were index cases and 62 were household contacts (HHC), of whom 25 HHC were infected (40.3%). Secondary attack rate (SAR) was highest among adults caring for a parent (n=4/4, 100%) and parents of index cases (5/10, 50%). Households whose income came from service work had greater risk of transmission compared to households whose primary income was technology (n=5/7;71.4% vs 3/8;37.5% respectively). Pediatric contacts were at lower risk of infection when compared to adult contacts (n=5/18, 27.8% vs n=20/44, 45.5% respectively). Conclusion. This study suggests that household transmission represents a key source of community-based infection of SARS-CoV-2. Allocating resources for education/ training regarding prevention among infected individuals and their close contacts will be critical for control of future outbreaks of SARS-CoV-2.