[Reading Science] How Did COVID-19 Infect 700 Million People?

Imperial College London Research Team
Conducts Deliberate Infection Experiment on Volunteers
Confirms Existence of 'Super Spreaders'
Identifies Correlation Between Severity and Infectivity
Home Rapid Tests Prevent Infection Spread

690,468,867 people. As of the 19th, this is the number of global COVID-19 virus infections compiled by the global statistics site Worldometer. How did the COVID-19 virus cause the worst infectious outbreak in human history? A research team in the UK has attracted attention by revealing secrets such as the existence of superspreaders through deliberate infection experiments.

The Imperial College London research team published a paper with these findings in the medical journal The Lancet on the 9th. The team inoculated the COVID-19 virus into the nasal mucosa of 34 young volunteers and monitored their condition. Among them, 18 tested positive and were treated and observed in isolation rooms for two weeks. The researchers measured the amount of virus by daily testing the palms, throats, nostrils, indoor air of the isolation space, and various surfaces.

The results confirmed the actual existence of "superspreaders," who emit significantly more virus into the air than others, a subject of controversy. In the experiment, 2 of the 18 infected individuals accounted for 86% of the aerosolized virus detected throughout the entire experiment period, emitting a large amount of virus. Although superspreaders who infected many others had been identified before, it was unclear whether this was due to more social contact or because they emitted more virus. Additionally, both of these superspreaders experienced only mild symptoms, suggesting no correlation between severity and infectiousness.

The study also confirmed the virus’s remarkable incubation characteristics. Participants underwent daily rapid antigen tests while in isolation, and none emitted detectable amounts of virus into the air before testing positive. Only small amounts of virus were detected on hands and mask surfaces. This also validated the importance of early response through home rapid testing. Most infected individuals experienced mild symptoms such as fatigue or muscle pain by the time they tested positive. This implies that prompt testing upon symptom detection can reduce severity, fatality rates, and virus spread.

The international journal Nature evaluated the study, stating, "It provides important public health answers regarding the correlation between severity and viral transmissibility, and whether home rapid antigen testing can help reduce virus spread," and "It sheds light on how widespread and unpredictable severity and infectiousness are among people." It also quoted Monica Gandhi, a professor of epidemiology at the University of California, saying, "The reason COVID-19 virus was so difficult to control was this diversity among people."

Some have pointed out ethical issues and limitations of this study. The currently dominant Omicron variant and other COVID-19 viruses generally infect by inhaling respiratory droplets directly or through mucous membranes of the eyes, nose, and mouth. However, this study was conducted by directly inoculating the virus into the nose. Considering that symptoms and severity of naturally infected COVID-19 patients vary depending on transmission route, virus type, and exposure amount, there may be limitations.