Dutch officials have said that the new mutant of the Covid-19 virus, omicron, was present in the Netherlands earlier than previously thought.
It was identified in two samples from two tests taken in the country between 19 and 23 November, before the discovery of the mutant was first reported in South Africa.
It is not clear whether the two people who took the test had visited South Africa.
It was previously believed that two planes flown in from South Africa on Sunday were the ones that brought the first cases of the mutant in the Netherlands.
It was found that fourteen people on board the two flights to the capital, Amsterdam, tested positive for the mutant Omicron, among 61 passengers who were found to be carrying the Corona virus.
Preliminary evidence suggests that the omicron mutant carries a higher risk of transmitting infection to vaccinated people. But scientists say it will take about three weeks before it is known how much the highly mutated strain affects the effectiveness of the vaccines.
The National Institute of Public Health in the Netherlands, which announced the first cases, said: “In a special PCR test, the samples showed an abnormality in the protein of the spines surrounding the virus.”
“This has raised concerns that the mutated Omicron may be involved. Health officials will inform the people concerned and begin the process of tracing the source and their contacts,” he added.
The institute also said that a number of different strains of Omicron were detected among the passengers on the two flights that arrived on Sunday.
A spokesman for the institute said: “This means that people are likely to have been infected independently of each other, from different sources and in different places.”
Written by: Michelle Roberts
BBC health editor
It is never expected to know exactly when and where the omicron first appeared.
South Africa alerted the world to the emergence of the new mutant on November 24, after discovering its first case. Since then, other countries have started searching for it and more cases have been identified around the world thanks to genetic sequencing tests.
But not all countries have the capacity to conduct these additional tests.
Even the UK, which is a technology leader, is not able to test every positive case of COVID-19 to determine which strain is responsible.
Meanwhile, PCR tests can hint at the possibility that a case of Covid was caused by Omicron, but they cannot say for sure.
Meanwhile, the Dutch authorities are seeking to contact and test the thousands of travelers who came from South Africa, Botswana, Eswatini, Lesotho, Mozambique, Namibia and Zimbabwe.
The United States, Canada, the United Kingdom and the European Union have all imposed restrictions on travel from South Africa amid concerns about the new mutation.
But UN Secretary-General Antonio Guterres said he was “deeply concerned” about the isolation of South Africa, adding that “the people of Africa cannot be blamed for the unethically low level of available vaccines.”
South African President Cyril Ramaphosa said the region had been widely discriminated against, adding that a ban would not be effective in preventing the spread of the new mutation.
A statement from the State Department said the travel ban is “the closest thing we can get to punishing South Africa for its development in genetic sequencing and its ability to rapidly detect new strains”.
He added that “excellent science should be praised, not punished.”