Table. Characteristics of new studies included in the present meta-analysis on the role of children in transmission of SARS-CoV-2 variants of concern within households, 25 August 2020–30 June 2022 (n = 48) .
| Reference | Location | Diagnosis of COVID-19 case | Study design/period (VOC) | Household size (contacts/index) | Follow-up duration for household contacts | Age of child group (years) | Detection of VOC; vaccination status reported |
|---|---|---|---|---|---|---|---|
| Sordo et al. 2022a [17] | Australia, New South Wales | Laboratory-confirmed COVID-19 cases | Retrospective observational study; July–October 2020 (pre-VOC) | 229 primary cases and 659 close contacts | Secondary cases were defined when a household contact became a confirmed COVID-19 case 2–14 days after the onset date of COVID-19 in the primary case | <18 | NA |
| Musa et al. 2021a [18] | Bosnia and Herzegovina | Laboratory-confirmed cases of SARS-CoV-2 infection | Prospective observational study; 3 August–19 December 2020 (pre-VOC) | 360 households and 747 contacts were analysed in this study (747/360). | Households were followed up for a total of 28 days after recruitment | 0–11, 12–17 | NA |
| Afonso et al. 2022 [19] | Brazil, Goiânia | Laboratory and clinical epidemiological criteria in line with recommendations of the Ministry of Health of Brazil and the WHO | Cross-sectional study; 15 June–28 October 2020 (pre-VOC) | 187 adults were included as index cases. 267 children household contacts were investigated (NA). | Children household contacts were recruited via phone calls and text messages to the adult index case within 10 days of diagnosis | 5–9, 10–14, 15–19 | NA |
| Wilkinson et al. 2021 [20] | Canada, Winnipeg Health Region | A confirmed case had laboratory confirmation, with detection of at least one specific gene target by a NAAT assay | Observational study; April 2020 (pre-VOC) | 102 primary cases and 279 household contacts | Contacts were followed for the 14-day period | 0–19 | NA; Y |
| Li et al. 2021a [26] | China, Wuhan | Laboratory-confirmed cases were individuals with positive detection of SARS-CoV-2 nucleic acid by RT- PCR using respiratory specimens | Retrospective observational study; 2 December 2019–18 April 2020 (pre-VOC) | 27,101 households with 57,581 household contacts were identified (24,985 households had only a single primary case) | Household contacts were told to isolate for an additional 14 days at home or designated facilities | 0–12, 13–19 | NA |
| Lyngse1 et al. 2021a [46] | Denmark | Positive SARS-CoV-2 laboratory test by RT- PCR | Cross-sectional study: 11 January–7 February 2021 (15% index infected with Alpha) | Index cases in in 5,241 households comprising of 2–6 persons (16,612/8,093) | Those who tested positive in the same household within the following 1–14 days were considered to be secondary cases | 1–10, 10–20 | Positive samples have been selected for WGS; NA |
| Lyngse2 et al. 2021 [47] | Denmark | Positive SARS-CoV-2 laboratory test by RT- PCR | Cross-sectional study; December 2021 (Omicron and Delta) | 2,225 indexes with the Omicron and 9,712 index cases with the Delta (in total 27,874/11,937) | 7-day follow-up period for potential secondary cases | 1–10, 10–20 | This study relies on variant PCR testing to determine if each primary case was Delta or Omicron; Y |
| Lyngse3 et al. 2022a [48] | Denmark | Positive SARS-CoV-2 laboratory test by RT- PCR; a primary case was also identified with the Omicron VOC BA.1 or BA.2 by WGS | Cross-sectional study; 20 December 2021–18 January 2022 (Omicron VOC BA.1 and BA.2) | 6,419 indexes with the Omicron BA.1 (13,358/6,419) and 2,122 index cases were BA.2 (4,587/2,122). | 7-day follow-up period for potential secondary cases | 1–10, 10–20 | Identified with the Omicron VOC BA.1 or BA.2 by WGS; Y |
| Lyngse4 et al. 2022 [49] | Denmark | Positive SARS-CoV-2 laboratory test by RT-PCR | Cross-sectional study; 21 June–26 October 2021 (Delta) | Households with 2–6 members, average 53,566 household members per 24,693 indexes | Secondary cases were defined as all cases testing positive within 1–14 days | 1–10, 10–20 | Delta index was Identified by RT-PCR; Y |
| Galow et al. 2021a [67] | Germany, Dresden | SARS-CoV-2 PCR-positive | Cross-sectional study; June 2020 (pre-VOC) | 139 PCR-confirmed index-case and 238 contacts | NA | <18 | NA |
| Loenenbach et al. 2021a [50] | Germany, Hesse | Positive SARS-CoV-2 laboratory test by PCR | Cross-sectional study; January–February 2021; (Alpha) | The study included 38 households with 92 contact persons | All contact persons were for 14 days followed up daily for symptoms via telephone calls | 1–6 | NA |
| Koureas et al. 2021a [29] | Greece, Larissa | Positive SARS-CoV-2 laboratory test by RT- PCR | Cross-sectional observational study; 8 April–4 June 2020; (pre-VOC) | 30 households and 223 household contacts | NA | 0–12, 13–19 | NA |
| Shah et al. 2021a [70] | India, Gujarat State | Laboratory-confirmed cases | Cross-sectional study, study; March–July 2020 (pre-VOC) | 72 paediatric index cases having 287 household contacts were included | Secondary case was defined as individual developing infection within 14 days from last contact with the index case | 0–18 | NA |
| Rajmohan et al. 2021 [51] | India, Kerala | Tested for SARS-CoV-2 either by real-time RT PCR or rapid antigen test | Prospective cohort study; 1 January–31 March 2021 | 101 SARS-CoV-2 index cases and 387 household contacts | Household contacts were followed up for 14 days | 0–4, 5–17 | NA |
| Jagdale et al. 2021a [31] | India, Pune City | RT-PCR-positive | Retrospective cohort study conducted in the month of June 2020 (pre-VOC) | 119 laboratory-confirmed primary cases and their 741 contacts | The primary contacts that turned RT-PCR positive on throat swab within 14 days of contact (irrespective of symptoms) with the confirmed case were counted in for estimating SAR | <16 | NA |
| Layan et al. 2022 [52] | Israel | Confirmed SARS-CoV-2 infections were defined by a positive PCR test, i.e., with a Cq value lower than 40 | Prospective cohort study; 31 December 2020 and 26 April 2021 (Alpha) | 210 HCW households with 215 index cases, including four co-index cases and their 687 household contacts (687/215) | At least 10 days of active symptom monitoring | 0–12 | The study took place when Alpha VOC represented up to 90% of infections in Israel; Y (only individuals ≥ 16 years old were eligible for vaccination) |
| Ogata et al. 2022a [53] | Japan, Itako | Cases were confirmed using PCR tests with a cycle threshold value of 40 | Observational study; December 2020–November 2021 (48% Delta+21% Alpha+31% wt) | The study enrolled 1,257 unvaccinated contacts from 580 households. | NA | 0–19 | Y |
| Akaishi et al. 2021 [33] | Japan, Sendai | Positive SARS-CoV-2 laboratory test by real-time RT-PCR | July 2020–March 2021 (pre-VOC) | Household contact group (NA/1,144) | Contact with a COVID-19 patient between 2 days before and 14 days after the onset of symptoms | 0–11, 12–17 | The study period was well before the replacement of major viral strains spreading in the locality from the original strains to N501Y mutant strains in May 2021 |
| Kuba et al. 2021 [34] | Japan, Okinawa | Confirmed by positive of their clinical specimens (nasopharyngeal swab etc) on SARS-CoV-2 N2 RT-PCR | Observational study; 14 February–31 May 2020; (pre-VOC) | Average (174/78) household members per confirmed index case | The health conditions of the close contacts were followed up for 14 days by PHC staff | 0–9, 10–19 | NA |
| Ng1 et al. 2022a [35] | Malaysia, Negeri Sembilan | Confirmed by RT-PCR | Retrospective observational study; 1 February–31 December 2020 (pre-VOC) | The study was conducted among the 185 households (848/185). | The household contacts were placed on strict quarantine at home or at a designated facility for 14 days | 0–12, 13–17 | The B.1.524 lineages were identified as the predominant circulating variants during the study period; NA |
| de Gier et al. 2021 [54] | Netherlands | A case was defined as a person with a positive SARS-CoV-2 PCR, loop-mediated isothermal amplification or antigen test | Retrospective cross-sectional study; August–September 2021; (Delta) | The final dataset contained 7,771 contacts of 4,921 index cases (7,771/4,921). | All household contacts were required to quarantine up to 10 days and get tested | 12–17 | Over 85% Delta variant among sequenced isolates starting from 5 July 2021; Y |
| Gorgels et al. 2021a [68] | Netherlands | Positive SARS-CoV-2 PCR or antigen test | Retrospective observational study; March 2021–June 2021. alpha variant (B.1.1.7) | 97 households and 249 household contacts | Household contacts were followed up for 14 days | 4–12 | WGS; NA |
| Soriano-Arandes et al. 2021a [72] | Netherlands | Any individual testing SARS-CoV-2-positive by RT-PCR or by antigen testing in a respiratory specimen | Prospective study; 1 July 2020 and 31 October 2020 (pre-VOC) | NA | NA | 0–5, 6–11, 12–16 | NA |
| Verberk et al. 2022a [55] | Netherlands, Belgium and Switzerland | Laboratory-confirmed positive SARS-CoV-2 RT-PCR test result in a household member (index case) and enrolled within 48 h following test result | Prospective cohort study; April 2020 until April 2021 | In 276 households with 920 participants (276 index cases and 644 household members) daily (co-primary case) | Self-sampling daily follow-up was continued until 21 days after last symptom onset in any household member | <12,12–18 | Households were included before the SARS-CoV-2 vaccination programme was (fully) rolled out and only a small proportion of the population had prior immunity |
| Reukers et al. 2022 [36] | Netherlands, Utrecht | Laboratory-confirmed SARS-CoV-2 infection was defined as at least one positive PCR on any of the clinical samples | Prospective cohort study; 24 March–6 April 2020 (pre-VOC) | A total of 55 households with 187 household contacts were included (187/55) | All household contacts were tested and subsequently followed up for 4–6 weeks | 0–11, 12–17 | NA |
| Jalali et al. 2022a [56] | Norway | Confirmed by PCR test | Retrospective cohort study; December 2021–January 2022 (Delta and Omicron) | In total, 1122 primary cases with confirmed Delta (41%) or Omicron (59%) and 2,169 household contacts (2,169/1,122) | Households of sizes 2–6 individuals, household contacts were monitored for ≤ 10 days after the test date of the primary case | 0–16 | Virus variant information was based on either PCR variant screening, WGS, or both; Y |
| Telle et al. 2021 [37] | Norway | Positive PCR results for SARS-CoV-2 | Observational study; 1 March 2020 and 1 January 2021 (NA) | The 7,548 families of the index cases comprised 26,991 individuals (26,991/7,548) | Tested positive by PCR within 7 days after the testing date of the index case | 0–19 | NA |
| Julin et al. 2021 [57] | Norway, Oslo/Viken | SARS-CoV-2 infection detected by real-time RT-PCR | Prospective longitudinal study; May–June 2020, and September 2020–April 2021 (Alpha and non-VOC) | 65 primary cases/households (18 infected with the Alpha variant, one with the Beta variant and 40 with other circulating non-VOC viruses) and their 135 household contacts | The first home visit for inclusion and sampling was termed Day 0, and seven further home visits were followed up for 6 weeks | 2–17 | WGS |
| Ng2 et al. 2022a [6] | Singapore | A confirmed COVID-19 case was defined as respiratory specimens positive for SARS-CoV-2 by RT-PCR | Retrospective cohort study; 1 March–31 August 2021 (Delta) | 8,470 Delta variant-exposed household close contacts linked to 2,583 index (8,470/2,583) | All identified close contacts underwent legally enforced quarantine for 14 days | 0-11, 12-17 | All positive cases with RT-PCR Cq < 30 were subjected to WGS for variant identification; Y |
| Yung et al. 2020 [38] | Singapore | Laboratory confirmation was based on RT-PCR testing of nasopharyngeal swabs | Observational study; March and April 2020 (pre-VOC) | 137 households with a total of 223 adults (index patients), 213 paediatric household contacts were included. | Household contacts were quarantined for 14 days from the last day of exposure | 0–10, 10–16 | NA |
| Cohen et al. 2022a [58] | South Africa | Positive SARS-CoV-2 laboratory test by RT-PCR | Prospective cohort study; July 2020–August 2021; (wt/Beta/Alpha/Delta) | 222 households were included. Average (1,251/222) household members per confirmed index case. We included 180 clusters from 101 households for analysis of HCIR. | Household contacts were prospectively followed active symptom monitoring through the 21-day period | <5, 5–12, 13–18 | All positive samples were tested to identify VOC using the AllplexTM SARS-CoV-2 Variants I assay (Seegene Inc., Seoul, Korea); Y |
| Song et al. 2022a [71] | South Korea | Laboratory SARS-CoV-2-positive cases | Observational study; November–December 2021 (Omicron) | 25 households, comprising 55 household members | NA | 0–6 | NA; Y |
| Martínez-Baz et al. 2022a [39] | Spain, Navarre | Positive SARS-CoV-2 laboratory test by RT-PCR or antigen test in a specific setting | Prospective cohort study; 11 May–31 December 2020 (pre-VOC) | Average 32,094 household members per 12,829 confirmed index cases | Those who tested positive within the 10 days were counted as cases | <5, 5–14 | NA |
| Posfay-Barbe et al. 2020a [69] | Switzerland | Nasopharyngeal specimens tested for SARS-CoV-2 by RT - PCR | Observational study; 10 March–10 April 2020 (pre-VOC) | 39 paediatric index patients and 111 household contacts | The median follow-up of the households was 18 days (IQR: 14–28) | <16 | NA |
| Watanapokasin et al. 2021 [59] | Thailand, Bangkok | Confirmed by RT-PCR | Retrospective study; 1 May–30 June 2021 (Alpha/Delta) | The 30 index cases were associated with 157 exposed household contacts (157/30) | 14-day follow-up period for household close contacts | <18 | NA; Y |
| Harris et al. 2021a [60] | United Kingdom | Laboratory-confirmed cases of COVID-19 (HOSTED dataset) | Cross-sectional study; 4 January–28 February 2021 (Alpha) | 1,018,842/102,662 | 14 days observable follow up for all contacts HOSTED dataset | <16 | Alpha; Y |
| Lopez Bernal et al. 2022 [40] | United Kingdom | PCR-positive | Prospective case-ascertained study; January–March 2020 (pre-VOC) | 269 primary/co-primary cases resided in 233 homes and 472 household contacts | Trained staff followed up all household contacts of confirmed cases 14 days or more | <18 | NA |
| Miller et al. 2021a [41] | United Kingdom | All SARS-CoV-2 infection laboratory-confirmed by RT- PCR with Cq values ≤39 considered positive | Cross-sectional study; 30 March and 17 November 2020 (pre-VOC) | 452 household contacts/181 primary cases | Index cases and their household contacts were followed daily for 14 days to ascertain symptoms and secondary transmission events | 0–10, 11–18 | NA |
| Singanayagam et al. 2022 [61] | United Kingdom, Greater London and Bolton | Positive SARS-CoV-2 laboratory test by RT- PCR | Retrospective observational study; 13 September 2020–15 September 2021 (Alpha/Delta/pre-Alpha) | 204/138 | NA | <18 (aged 5 years or older) | WGS; Y |
| Chu et al. 2021a [66] | United States, Atlanta | Laboratory tested positive | Retrospective cohort study; 17 July–24 August 2020 (pre-VOC) | 224 index patients and 526 household contacts | 2 days prior to and up to 10 days after illness onset | 7–19 | NA |
| Waltenburg et al. 2022a [9] | United States, California and Colorado | Positive RT-PCR for SARS-CoV-2 | Prospective cohort study; January–April 2021 (Alpha) | 127 households with a single primary case and 316 household contacts were available for analysis | 14-day follow-up period for household close contacts | 0–11, 12–17 | WGS conducted on at least one nasopharyngeal specimen from participants with a RT-PCR Cq < 35 |
| Donnelly et al. 2022 [62] | United States, California and Colorado | Positive RT-PCR for SARS-CoV-2 | Observational study; January–April 2021 (alpha+non-VOC) | 127 households with 322 household contacts | The CDC investigators visited households at enrollment (day 0) and at closeout (day 14) | 0–17 | Nasopharyngeal specimens with an RT-PCR Cq < 35 were selected for WGS; Y |
| Baker et al. 2022 [7] | United States, four jurisdictions | Positive SARS-CoV-2 nucleic acid amplification test result or antigen test result | Descriptive study and contact tracing; 21 November 2021–3 February 2022 (Omicron) | Enrolled households included 183 index cases and 439 household contacts (439/183) | 14-day follow-up | 0–4, 5–11, 12–17 | Index case with sequence-confirmed Omicron variant; Y |
| Liu et al, 2021a [63] | United States, Los Angeles, California | Laboratory-confirmed positive SARS-CoV-2 by RT-PCR | Prospective case-ascertained transmission study; December 2020 and February 2021 | 15 paediatric index cases (<18 years-old) and 50 household contacts | 14-day follow-up | <18 | NA |
| Tanaka et al. 2021 [44] | United States, Los Angeles, California | Confirmed by RT-PCR | Retrospective observational study; 17 June–31 December 2020 (pre-VOC) | Households ranged from 2 to 11 members living together (489/105) | Individuals followed up for a median of three visits (IQR: 2–4) over 15 days (IQR: 7–27) | 0-11, 12-17 | NA; Before vaccination rollout |
| McLean et al. 2022a [64] | United States, Nashville, Tennessee and Wisconsin | Laboratory-confirmed SARS-CoV-2 infection by RT-PCR | Cross-sectional study; 21 April 2020 to 30 April 2021 (pre-VOC) | 404 household contacts/226 primary cases | Index cases and their household contacts were followed daily for 14 days to ascertain symptoms and secondary transmission events | 0–4, 5–11, 12–17 | NA |
| Sachdev et al. 2021 [65] | United States, San Francisco | Patients with laboratory-confirmed COVID-19 (positive RT-PCR) | Observational study; 29 January–2 July 2021 (Alpha/Beta/Delta/Gamma) | Among 248 fully vaccinated patients with breakthrough infection, 105 were identified as the index cases (179/105) | NA | <18 | WGS; Y |
| Laws et al. 2021 [42] | United States, Utah and Wisconsin | Positive SARS-CoV-2 laboratory test by RT-PCR or ELISA | Retrospective cohort study; 22 March–25 April 2020 (pre-VOC) | Among 58 households, 188 contacts were enrolled (120 adults; 68 children) | Contacts were assessed daily symptoms prospectively for 14 days and obtained specimens for PCR test and serology testing | <1, 1–4, 5–12, 13–17 | NA |
CDC: Centers for Disease Control and Prevention; Cq: quantification cycle; HCIR: household cumulative infection risk; HCW: healthcare worker; IQR: interquartile range; NA: not applicable; NAAT: nucleic acid amplification test; PHC: public health centre; SAR: secondary attack rate; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; VOC: variants of concern; WGS: whole genome sequencing; WHO: World Health Organization; wt: wildtype; Y: Yes.
a 27 studies contained eligible data were included for the index case meta-analysis.