This is a summary, written by members of the CITF Secretariat, of:

Bhatt M, Plint AC, Tang K, Malley R, Huy AP, McGahern C, Dawson J, Pelchat M, Dawson L, Varshney T, Arnold C, Galipeau Y, Austin M, Thampi N, Alnaji F, Langlois MA, Zemek RL. Household transmission of SARS-CoV-2 from unvaccinated asymptomatic and symptomatic household members with confirmed SARS-CoV-2 infection: an antibody-surveillance study. CMAJ Open. Apr 2022, 10 (2) E357-E366; DOI: 10.9778/cmajo.20220026.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

In a study published in the Canadian Medical Association Journal, CITF-funded researcher Dr. Marc-André Langlois from the University of Ottawa and colleagues found that half of those residing in a household in which someone became infected with SARS-CoV-2 became infected as well. While adults were more likely to spread infection than children, children transmitted infection to roughly one-third of their household members. Children and adults were equally likely to be infected by the infected adult or child in their home.

Key findings:

  • Of the 454 household contacts (88.1%) who reported being tested for SARS-CoV-2 before the study commenced, 158 (34.8%) had a positive result within 14 days of coming into contact with an infected household member.
  • A total of 487 household contacts (94.6%) (246 children, 241 adults) had SARS-CoV-2 antibody testing, of whom 239 had a positive result (infection from primary contact – 49.1%)
  • Of the 239 who tested positive, 88 (36.8%) were asymptomatic; asymptomatic rates were similar for children (51/130 [39.2%]) and adults (37/115 [32.2%] (odds ratio [OR] 1.3)
  • Adults were more likely than children to transmit SARS-CoV-2 (ORThe Odds Ratio (OR) represents the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure. 2.2).
  • The rate of transmission from asymptomatic primary participants (that is to say, the person who was initially infected) to household contacts was 35.3% (95% CI 18.5%–56.8%), and the rate of transmission from symptomatic primary participants was 50.7% (95% CI 44.2%–57.1%) (OR 0.6, 95% CI 0.2–1.4).
  • Predictors of household transmission included household density (number of people per bedroom), relationship between individuals and number of cases in the household. The odds of transmission from asymptomatic (OR 0.6) versus symptomatic (OR 0.9) primary participants to household contacts were uncertain.

People with SARS-CoV-2 infection transmit extensively within their households, a finding which should inform public health policy. Asymptomatic spread occurred and should be accounted for in the formulation of public health and travel policies. Study findings have implications for in-person school and activities because the risk of transmission may be high when masks are not worn continuously or consistently in poorly ventilated settings. Nonpharmacologic interventions should continue to be considered for congregate settings.

A total of 695 participants from 180 households, wherein at least one person tested positive for SARS-CoV-2 by PCR, were enrolled during the study between September 2020 and March 2021. ELISA assay was used to evaluate SARS-CoV-2 specific antibodies against the spike and nucleocapsid protein.