According to the results of a new research study at least one in three people infected with the SARS-CoV-2 virus do not have any symptoms. The study carried out a systematic review of 61 previously published studies 43 which used PCR testing, and 18 studies used antibody testing to cross-reference their data.

The study, published in the Annals of Internal Medicine, examined reports collected from 1.8 million people and was conducted by scientists from Scripps Research Institute in San Diego, California. In addition, the study incorporated results from two large surveys conducted in England and Spain, which tested the presence of COVID-19 antibodies in over one million people.

“In light of the data presented here we believe that COVID-19 control strategies must be altered, taking into account the prevalence and transmission risk of asymptomatic SARS-CoV-2 infection,” the study’s authors conclude. “More research will be needed to determine their efficacy in preventing asymptomatic infection.”

The study’s lead authors, Drs. Eric Topol and Daniel Oran note the significant asymptomatic rate, with asymptomatic cases comprising a major portion of COVID-19’s global footprint.

“The biggest implication of this is that we need to test far more widely and frequently, and not confined to people with symptoms,” said Dr. Topol, founder and director of the Scripps Research Translational Institute and professor of Molecular Medicine at Scripps Research. “We need to urgently get rapid home antigen tests to every household for daily use.”

In his interview with CTV News, Dr. Brian Conway, Medical Director of the Vancouver Infectious Diseases Centre, said the results of the study demonstrate the importance of testing asymptomatic individuals for the COVID-19 disease.

“If we identify groups of individuals for whom the transmission network is unclear, I think there is a role for testing larger numbers of asymptomatic individuals to… interrupt those transmission networks more effectively,” Dr. Conway said.

Moreover, the study’s authors suggest that using inexpensive, at-home testing for COVID-19 infection could be useful in identifying pre-symptomatic and asymptomatic individuals, helping to stop further spread of the coronavirus.

“Now we know with certainty that asymptomatic infection is a notable feature of SARS-CoV-2,” said Dr. Topol. “It’s time that we translate this knowledge into smarter testing practices that will help to bring COVID-19 under control.”

Currently, PCR testing can be used to determine early-term active infections, while antibody-based tests can be used to identify early phases of antibody production. Using a combination of these methods, it is possible to examine the entire infection cycle to better understand the scope of COVID-19 infection in the community. Adapting these testing methods accordingly can contribute to our understanding of the risk within each community or workplace.