SARS-CoV-2 Transmission From People Without COVID-19 Symptoms: Implications for Public Health Strategies

A study published in JAMA Network Open, led by Michael A. Johansson and colleagues, provides significant insights into the transmission dynamics of the SARS-CoV-2 virus, particularly from individuals without COVID-19 symptoms.

The study’s key findings are as follows:

  1. Objective and Importance: The study aimed to assess the proportion of SARS-CoV-2 transmissions that occur from asymptomatic individuals, recognizing the importance of this data for directing public health resources and messaging to mitigate the spread of COVID-19.
  2. Methodology: Utilizing a decision analytical model, researchers analyzed the transmission from individuals who were presymptomatic, asymptomatic (never symptomatic), and symptomatic. They varied the proportion of transmission from asymptomatic individuals and the infectious period duration based on existing meta-analysis data, setting the median incubation period at 5 days and infectious period at 10 days.
  3. Key Findings:
    • Approximately 59% of all SARS-CoV-2 transmissions were estimated to originate from asymptomatic individuals, comprising 35% from presymptomatic and 24% from never symptomatic individuals.
    • This suggests that more than half of all COVID-19 transmissions may occur from individuals who do not exhibit symptoms.
    • The model indicates that effective control of COVID-19 spread cannot solely rely on identifying and isolating symptomatic cases.
  4. Limitations:
    • The study acknowledges limitations, including the simplicity of the model to represent the complex dynamics of SARS-CoV-2 infectiousness over time.
    • There’s uncertainty in the exact proportions of presymptomatic and never symptomatic transmission and variability in different populations.
    • The study’s estimates might represent the lower end of asymptomatic transmission proportion, considering interventions that reduce symptomatic transmission.
  5. Conclusions:
    • In light of these findings, the study suggests that effective control of COVID-19 requires strategies beyond identifying and isolating symptomatic cases.
    • Measures such as wearing masks, practicing hand hygiene, maintaining social distancing, and strategic testing of asymptomatic individuals are crucial to control the spread of the virus.
    • The study emphasizes the need for multiple measures that address transmission risk from asymptomatic individuals to effectively control SARS-CoV-2.

This study highlights the significant role of asymptomatic transmission in the spread of COVID-19 and underscores the importance of comprehensive public health strategies that consider both symptomatic and asymptomatic carriers of the virus​​​​.

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