Coronavirus infection transmission rate and the potency of infection spread from asymptomatic patients is still “unknown”, World Health Organization clarified on Tuesday. This was after Dr. Maria Van Kerkhove, WHO’S COVID-19 technical lead said on Monday that infection spread from asymptomatic cases is “very rare”. The fact that this observation was based on a small study group, makes it not reliable.
Director of WHO’s Health Emergencies Programme, Dr. Michael Ryan said that undoubtedly there is transmission of infection from asymptomatic sources and that he was “absolutely convinced” about it. Just the question left is that “how much” infection spread rate is from patients displaying no symptoms.
Dr. Maria Van Kerkhove, who is also the WHO’S Head of Emerging Diseases clarified the distinctive features between three categories of coronavirus patients/ carriers.
- Asymptomatic patients – these are the ones who never develop any symptoms to infection, and therefore sometimes might go undetected.
- Pre-symptomatic – These patients do not have any symptoms when they are tested positive, but they develop them later on.
- Mild symptomatic – These people have very mild or common (atypical) symptoms and they usually do not realize they have the infection, and go undetected.
These minor differences between categories, which are seldom not mentioned in the reports, along with small sample size for study make it significantly difficult to draw any conclusions regarding carriers and spread of coronavirus infection.
But Dr. Van Kerkhove suggested that available evidences indicate lower infection spread instances from patients who never develop the symptoms or are asymptomatic, when compared to patients with mild or moderate-severe symptoms.
According to studies conducted by the WHO in various random sample groups of asymptomatic cases, when contact tracing was done it was discovered that there were very low secondary infection cases among people who came in contact with asymptomatic patients.
WHO published in “guidance on wearing masks” on weekend, based on the study concluding “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.”
The Office of National Statistics (ONS) in UK after consistent sample testing of patients concluded that only 29% of positive tested patients of COVID-19 reported “any evidence of symptoms” when they were tested positive, or previous or following visits.
Symptomatic patients – highest risk carriers
Contact tracing sample studies in many countries provides evidence that “true asymptomatic” cases “rarely transmit” infection. But the studies also indicate that there can be infection transmission before or on the day symptoms appear when they are mild in severity, stated Prof. Babak Javid who is an Infectious Diseases Consultant at the University of Cambridge.
Around three days before the patients first develop symptoms, there can be a detectable load of virus present in their system, which is capable of transmission relatively higher just before or on the day of symptoms appearance.
The asymptomatic cases can transmit the infection, but the relative high infection spread by symptomatic patients provides suitable evidence that they are the “highest risk” category of carriers.
The evidence collected through studies suggests – a positive case doesn’t directly indicate the transmission capacity of the patient or how much virus is in their system, also known as “Viral Load”. But when a patient displays symptoms like sneezing and coughing and the amount of contact he has with other people, directly influences how likely he can transmit the infection. It has been substantially determined that coronavirus mainly “passes through infectious droplets”. This determines that when a patient sneezes or coughs, he is most prone to pass on the infection, pointed out Dr. Van Kerkhove.