About four in ten COVID-19 cases are asymptomatic, according to a new meta-analysis.
The research performed by a team from Beijing's Peking University included 95 studies conducted on three different continents, representing almost 30 million people who were tested for Covid.
Overall, about 40 percent of Covid patients in the analysis had asymptomatic cases. For some sub-groups, like pregnant women and travelers on airplanes and cruises, the figure was about 50 percent.
The study shows that many people who may feel fine are still at risk of spreading the virus, and demonstrates the importance of widely available Covid testing, particularly for travelers.
A new study finding that 40% of Covid cases are asymptomatic demonstrates the need for widely available testing. Pictured: Covid testing in Houston, Texas, August 2021
The study found that certain populations, such as air and cruise travelers and pregnant women, were more likely to be asymptomatic than the overall population
Covid cases can range from severe symptoms that land patients in the hospital - to mild, cold-like symptoms, or no symptoms at all.
Asymptomatic cases may help the coronavirus spread from person to person, because people can carry it without realizing they're sick.
Such cases distinguish the novel coronavirus from past SARS viruses, which typically don't spread without symptoms.
The new study on asymptomatic Covid infection suggests that they may be even more common than previously thought.
Researchers compiled and analyzed data from a number of studies focused on asymptomatic cases.
The analysis was published Tuesday in JAMA Network Open.
It included 95 scientific studies in total, including 35 done in Europe, 32 in North America, and 25 in Asia.
The researchers defined an asymptomatic case as a person who tested positive on a PCR test - considered to be the gold standard for Covid testing - while not feeling any symptoms at the time.
Overall, the 95 studies included 29.8 million individuals who were tested for the virus.
Among the population, 11,500 had asymptomatic Covid infections - about 0.25 percent.
The researchers also used 77 out of the 95 studies to estimate the number of Covid cases that occurred without symptoms.
Those studies included about 20,000 Covid cases in total, of which 40.5 percent were asymptomatic.
Certain populations had higher numbers of
