- A study analysed the routes that the coronavirus took before the pandemic.
- Travel routes to China, Italy and Iran contributed most to the spread of Covid-19.
- It took the virus 11 weeks to affect 50% of the world.
How did the coronavirus go from an outbreak in a single Chinese city to a global pandemic?
It turns out that it took travellers from only three countries to spread the highly contagious Covid-19 across most of the world.
Researchers analysed travel patterns of early confirmed cases outside of China to determine the route the virus took around the world.
They used information collected from 1 200 cases from 68 affected countries during the pre-pandemic period from 31 December, 2019, to 10 March, 2020.
"We analysed reported travel to affected countries among the first cases reported from each country outside mainland China, demographic and exposure characteristics among cases with age or gender information, and cluster frequencies and sizes by transmission settings," wrote the researchers.
During the pre-pandemic period, about 50% of 199 countries and locations had reported at least one case of Covid-19.
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The countries affected during the first 11 weeks
In the first three weeks, cases outside China were only reported in Japan and Thailand.
In the fourth and fifth week, 24 more countries reported cases. Germany was the first affected European country, the USA was the first country in the Americas, and the United Arab Emirates the first Eastern Mediterranean area. Up until week nine, the number of affected countries didn't go up – but it then grew exponentially.
The first affected African country was Algeria, and by 10 March, 13% of African countries were affected.
On 5 March, South Africa reported its first case in the second-last week of the pre-pandemic period. It was a man in his 30s who had travelled to Italy on holiday.
"Only 13 (43%) of 30 countries in the Western Pacific region had reported cases by week 11, and most countries without any cases were remote island states with relatively small population sizes."
The main countries of infection
The researchers found that almost two-thirds of early cases had travel links to China, Italy and Iran, where the average age of infected persons was 51 years, with only 3% of 762 early cases being people younger than 18 years.
About 22% of first cases in countries had travelled to China, 11% to Iran, 27% to Italy and 15% to other affected countries.
While travel from China contributed to a big chunk of first cases in the Western Pacific and South-East Asian countries, African, European and American countries were the most exposed to travel to and from Italy. Travel from Iran helped the virus spread in the Eastern Mediterranean region, although a few early cases had no reported travel histories.
Travel from France was also a major spreader to the African region.
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Community transmission bigger than household transmission
Among the 874 early cases, 79% were from high-income countries, whereas fewer than 1% were from low-income countries. In the 1 200 analysed cases, there were 52 deaths, most around the age of 72, and no children died. Only about 2% were healthcare workers in the beginning stages of the pandemic.
While the spread from these travellers was thought to be mostly clustered around household transmissions, the researchers found much higher spread in workplace and community settings. Many of the large clusters were attributed to faith-based gatherings, as well as healthcare settings, like hospitals.
This bolsters the argument for physical distancing to better curb the spread of the virus.
"Although most countries and locations in the European, Eastern Mediterranean, and South-East Asian regions reported confirmed cases by the time the WHO (World Health Organisation) characterised the outbreak as a pandemic, only a third of countries in the Americas and African regions had reported cases, suggesting delayed introduction, delayed detection, or both."
It also showed how travel from only three countries with widespread outbreaks might have fuelled the global pandemic.
How SARS and MERS compare
Another important point highlighted by the study was how the coronavirus spread a lot faster than its predecessors, SARS and MERS. In 11 weeks, only seven countries had reported 6 500 cases of SARS, and three countries had reported nine cases of MERS.
With Covid-19, ninety-nine countries reported more than 100 000 cases in the same time frame. The researchers hypothesised that asymptomatic and presymptomatic spread might have played a bigger role in the current pandemic than with SARS and MERS.
While the researchers had access to a massive global database, there were some limitations to consider.
Because they only focused on data with gender and age information, it only represented 4% of global confirmed early cases, and more than three-quarters of cases without this information were from the three countries with the highest case counts at the time, i.e. Iran, Italy and South Korea.
Also, the first case for each country might well not have been the "true" first case, as it depended on who tested first. Early global detection was very limited and varied from country to country.
However, this kind of statistical research can prove valuable to inform countries' future preparations and responses to Covid-19 and other pandemics.
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