A World Health Organization scientist Dr Maria Van Kerkhove has clarified that to what extent coronavirus transmission comes from asymptomatic people is still not known clearly.
Dr Maria said that it is “very rare” for people with no symptoms to transmit the infection on. Her observation, however, is based on a small set of studies.
Majority of studies suggests that symptomatic people are the most infectious, but the infection can be passed on prior to the development of symptoms. On the one hand number of people test positive for the virus with no symptoms, it is yet unknown how many of these people go on to infect others.
Dr Van Kerkhove claimed that the studies she had been discussing are a result of regions that had carried out aggressive contact tracing. As per these shreds of evidence, the number of secondary infections from asymptomatic people is very rare. But as it was earlier said that this study is based on a small sample size so it cannot be generalised for the whole world.
Dr Van Kerkhove, who is the head of emerging diseases at WHO, categorised infected people in three categories, one is those People who never develop any symptoms (asymptomatic), two those persons who test positive when they don’t yet have symptoms but later they develop symptoms (pre-symptomatic), and the last are those with very mild or atypical symptoms who do not realise they have coronavirus.
Dr Kerkhove said that Some reports trifurcate into these categories while others studies do not. The relatively small sample makes it difficult to draw any rigid conclusions.
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Weight of evidence substantiates that people who never develop any symptoms are not major contributors to transmission.
This led the WHO to publish in guidance on wearing masksthat “The available evidence from contact tracing reported by member states suggests that asymptomatically-infected individuals are much less likely to transmit the virus than those who develop symptoms”
In England, the Office for National Statistics (ONS) has been regularly testing a sample of the population.
It has found that, of those who have so far tested positive for Covid-19, only 29% reported “any evidence of symptoms” at the time they were tested, or at the previous or following visits.
Contact-tracing work from various countries shows that while purely asymptomatic cases transmit infection very rarely. However, the transmission of the virus can occur on the day symptoms first appear or before that day when they develop very mild symptoms.
People may have traceable amounts of the virus in their bodies around three to four days before developing any symptoms and these people are a potential source of transmission during this period. Though the asymptomatic people do seem to be capable of transmission, current studies still suggest that the symptomatic people are the highest posers.
A positive result alone is not the measurement of the amount of virus in someone’s body system. Viral load along with whether an infected person is sneezing and coughing and what kind of contact they are having with other people influences how likely they are to pass the illness on.
Dr Van Kerkhove marked that “since coronavirus mainly passes through infectious droplets, it is when people are coughing or sneezing that they are most able to transmit the disease.”