RIO DE JANEIRO, BRAZIL – Studies have shown that people who have contracted the novel coronavirus are more infectious when they present the initial symptoms, said Maria van Kerkhove, epidemiologist and World Health Organization (WHO) technical head for the pandemic, in a statement released on Tuesday.
She said a subgroup of people do not develop symptoms, but may still infect others, and up to 40 percent of transmissions can occur through asymptomatic cases.
This statement was made the day after a report was released which noted that cases of asymptomatic transmission are rare and that they have not increased the spread of the virus. “It’s very rare,” said the epidemiologist and chief technician at W.H.O.
Experts in infectious diseases quickly challenged the comment made on Monday, saying that this guideline could create problems as countries try to come out of isolation.
“I was quite surprised by the W.H.O. statement,” said Liam Smeeth, professor of clinical epidemiology at the London School of Hygiene and Tropical Medicine, who added that he had not seen the data on which Kerkhove’s statement was based.
“It conflicts with my perception of the current scientific evidence that asymptomatic people – who never have any symptoms – and pre-symptomatic people are a significant source of infection for others.
W.H.O. officials were not immediately available to comment on Tuesday. Van Kerkhove was expected to answer questions on a social media session on Tuesday.
Smeeth and other experts said understanding the risks of transmission among people with little or no symptoms is crucial, now that governments are starting to relax the isolation measures they implemented in an effort to slow the spread of the pandemic and gradually replace them with case tracking and containment plans.
“This has major implications for screening/detection/confinement measures being implemented in many countries,” said Babak Javid, an infectious disease consultant at Cambridge University Hospitals.
Some experts say it is not uncommon for infected people not to show symptoms.
Not yet submitted to the scientific community, a German study in May based on 919 people in the Heinsberg district – which recorded one of the country’s highest death tolls – found that about one in five people infected is asymptomatic, but data showing the likelihood of them transmitting the disease is scarce.
Keith Neal, professor of infectious disease epidemiology at the University of Nottingham in the United Kingdom, said that while it is unclear what role asymptomatic transmission plays in new infections, it is known that people with symptoms are largely responsible for the spread of the disease.
Source: Reuters