The earliest global spread of the novel coronavirus came from travel involving mostly three countries: China, Italy and Iran, researchers reported Wednesday.
Three-quarters of cases reported outside of China in January and February were linked to travelers from an affected country, mostly those three, a team at the US Centers for Disease Control and Prevention found.
“Cases with travel links to China, Italy, or Iran accounted for almost two-thirds of the first reported Covid-19 cases from affected countries,” the CDC’s Dr. Fatimah Dawood and colleagues wrote in the journal Lancet Infectious Diseases.
“Our findings suggest that travel from just a few countries with substantial SARS-CoV-2 transmission may have seeded additional outbreaks around the world before the characterization of Covid-19 as a pandemic on March 11, 2020,” Dawood added in a statement.
The team went through online reports from national ministries of health and other government agency websites, social media feeds, and news releases to tally up all coronavirus cases reported between December 31 and March 10.
Half of the early cases in Africa were linked to travel from Italy, they found. Travelers from Italy also carried the virus in a third of the earliest cases elsewhere in Europe and the Americas.
The analysis also showed that large gatherings were a source of spread.
“Four large clusters in our analysis, and large outbreaks reported elsewhere, have been linked with transmission in faith-based settings, highlighting the need to partner with faith-based organizations when designing and implementing community mitigation efforts,” the CDC’s Dr. Philip Ricks, who worked on the analysis, said in a statement. “Six healthcare-associated clusters were also identified, underscoring the need for strict infection prevention and control practices and monitoring health-care workers for signs of illness.”
While many studies have confirmed that the virus originated in China, genetic analysis shows that a new strain arose in Europe, likely Italy, early in the pandemic and that strain predominated in the US.