Household Transmission and Symptomology of Severe Acute Respiratory Syndrome Coronavirus 2 Alpha Variant among Children-California and Colorado, 2021

Abstract

Objective: To assess the household secondary infection risk (SIR) of B.1.1.7 (Alpha) and non-Alpha lineages of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among children.

Study design: During January to April 2021, we prospectively followed households with a SARS-CoV-2 infection. We collected questionnaires, serial nasopharyngeal swabs for reverse transcription polymerase chain reaction testing and whole genome sequencing, and serial blood samples for serology testing. We calculated SIRs by primary case age (pediatric vs adult), household contact age, and viral lineage. We evaluated risk factors associated with transmission and described symptom profiles among children.

Results: Among 36 households with pediatric primary cases, 21 (58%) had secondary infections. Among 91 households with adult primary cases, 51 (56%) had secondary infections. SIRs among pediatric and adult primary cases were 45% and 54%, respectively (OR, 0.79; 95% CI, 0.41-1.54). SIRs among pediatric primary cases with Alpha and non-Alpha lineage were 55% and 46%, respectively (OR, 1.52; 95% CI, 0.51-4.53). SIRs among pediatric and adult household contacts were 55% and 49%, respectively (OR, 1.01; 95% CI, 0.68-1.50). Among pediatric contacts, no significant differences in the odds of acquiring infection by demographic or household characteristics were observed.

Conclusions: Household transmission of SARS-CoV-2 from children and adult primary cases to household members was frequent. The risk of secondary infection was similar among child and adult household contacts. Among children, household transmission of SARS-CoV-2 and the risk of secondary infection was not influenced by lineage. Continued mitigation strategies (eg, masking, physical distancing, vaccination) are needed to protect at-risk groups regardless of virus lineage circulating in communities.

Keywords: COVID-19; alpha variant; children; household transmission.

Figure 2

Symptoms of COVID-19 among pediatric (n = 97) and adult (n = 172) household cases. A, Frequency of symptoms by age. B, ORs and 95% CIs for the presence of symptoms, comparing pediatric cases (n = 97) with adult household cases (n = 172). ^aSymptoms were categorized as constitutional (measured or subjective fever, chills, myalgia, and fatigue), upper respiratory (runny nose, nasal congestion, and sore throat), lower respiratory (cough, difficulty breathing, shortness of breath, wheezing, and chest pain), neurologic (headache, loss of taste, and loss of smell), and gastrointestinal (nausea and/or vomiting, diarrhea, and abdominal pain). ^bUnadjusted ORs and 95% CIs were estimated using generalized estimated equations with an exchangeable correlation matrix to account for household clustering. ORs and 95% CIs were graphed on a log scale.

Figure 4

SIR of SARS-CoV-2 among household contacts, by age and SARS-CoV-2 lineage of primary cases, California and Colorado, January to April 2021. To account for household clustering, ORs and 95% CIs were calculated using GEEs with an exchangeable correlation matrix and used to compare the SIRs of the primary case to assess transmission risk (the probability of transmission from the primary case to household contacts) by age group (pediatric vs adult) and lineage group (B.1.1.7 [Alpha] vs non-Alpha). Four pediatric and 45 adult household contacts reported prior SARS-CoV-2 infection or seropositivity and were excluded from the SIR calculations. Specimens from 5 primary pediatric cases did not undergo sequencing; therefore, a lineage was not assigned to these individuals.

Figure 6

SIR of SARS-CoV-2 among household contacts, by age and SARS-CoV-2 lineage, California and Colorado, January to April 2021. To account for household clustering, ORs and 95% CIs were estimated using GEEs with an exchangeable correlation matrix and used to compare SIRs of household contacts to assess infection risk (the probability of infection among household contacts) by age group (pediatric vs adult) and lineage group (B.1.1.7 [Alpha] vs non-Alpha). Four pediatric and 45 adult household contacts reported prior SARS-CoV-2 infection or seropositivity and were excluded from the SIR calculations. Lineages were assigned to uninfected pediatric household contacts based on the lineage of the household primary case. Eleven uninfected pediatric household contacts did not have a lineage assigned because specimens from primary cases did not undergo sequencing.

Figure 1

Enrollment of households in a COVID-19 household transmission investigation, California and Colorado, January to April 2021.

Figure 3

Symptoms of COVID-19 among pediatric household cases by SARS-CoV-2 lineage (n = 92). A, Frequency of symptoms by lineage. B, ORs and 95% CIs for the presence of symptoms, comparing pediatric cases with B.1.1.7 (Alpha) lineage (n = 60) to pediatric cases with non-Alpha lineages (n = 32). ^aSymptoms were categorized as constitutional (measured or subjective fever, chills, myalgia, and fatigue), upper respiratory (runny nose, nasal congestion, and sore throat), lower respiratory (cough, difficulty breathing, shortness of breath, wheezing, and chest pain), neurologic (headache, loss of taste, and loss of smell), and gastrointestinal (nausea and/or vomiting, diarrhea, and abdominal pain). ^bUnadjusted ORs and 95% CIs were estimated using generalized estimated equations with an exchangeable correlation matrix to account for household clustering. ORs and 95% CIs were graphed on a log scale.

Figure 5

SIR of SARS-CoV-2 among household contacts, by age and SARS-CoV-2 lineage of pediatric primary cases, California and Colorado, January to April 2021. To account for household clustering, ORs and 95% CIs were calculated by using GEEs with an exchangeable correlation matrix and used to compare SIRs of the primary case to assess transmission risk (the probability of transmission from the primary case to household contacts) by age group (pediatric vs adult) and lineage group (B.1.1.7 [Alpha] vs non-Alpha). Four pediatric and 45 adult household contacts reported prior SARS-CoV-2 infection or seropositivity and were excluded from the SIR calculations. Specimens from 5 primary pediatric cases did not undergo sequencing and therefore a lineage was not assigned to these individuals.

Figure 7

SIR of SARS-CoV-2 among pediatric household contacts, by age and SARS-CoV-2 lineage, California and Colorado, January to April 2021. To account for household clustering, SIRs were estimated using GEEs with an exchangeable correlation matrix. ORs and 95% CIs were used to compare SIRs of household contacts to assess infection risk (the probability of infection among household contacts) by age group (pediatric vs adult) and lineage group (B.1.1.7 [Alpha] vs non-Alpha). Four pediatric household contacts reported prior SARS-CoV-2 infection or seropositivity and were excluded from the SIR calculations. Lineages were assigned to uninfected pediatric household contacts based on the lineage of the household primary case. Eleven uninfected pediatric household contacts did not have a lineage assigned because specimens from primary cases did not undergo sequencing.

Figure 8

Phylogenetic tree of representative SARS-CoV-2 genomes obtained from households in a COVID-19 household transmission investigation, by age and SIR, California and Colorado, January to April 2021. Sequence data were obtained for 212 household members from 104 households. Circles denote adult primary cases (n = 73); triangles denote pediatric primary cases (n = 31). A SIR of 50% or greater was binned as high and represented in blue (n = 62); a SIR of less than 50% was binned as low and represented in yellow (n = 35); gray denotes the absence of susceptible contacts within the household (n = 7).