There have been reports regarding the potency of COVID-19 in Italy, deriving from comments made by Prof Alberto Zangrillo.
Prof Francois Balloux, Professor of Computational Systems Biology and Director of UCL Genetics Institute, University College London (UCL), said:
“There is no evidence for the SARS-CoV-2 having become more or less virulent/transmissible. The genetic composition of the viral population has in fact not changed much since it emerged. For a look at the latest results in the scientific literature (preprint) on the evolution of its transmissibility see https://doi.org/10.1101/2020.05.21.108506.
“The outbreak in Italy has been waning over recent weeks despite relaxation of the social distancing measures previously in place. This is line with what has been observed in most European countries. The extent to which this is only due to residual social distancing measures in place, or whether seasonality or some other factors are playing a role remains debated. That said, we should definitely not rule out a second epidemic wave later this year.
“The lockdowns were necessary to avoid hospital being overrun. Social distancing measures are being progressively relaxed in countries where the outbreak is under control. I do not believe these comments are helpful or reflect the current scientific evidence.
“Viral load of swab tests will vary over the course of an infection. When compared on the same day post-infection, viral load can correlate with symptom severity. Though, viral dose might also be a function of the initial infectious dose (the number of virions that a patient got infected with). Transmission outdoors is likely to be characterised by lower infectious dose and less severe symptoms, than transmission indoors.
“There is no evidence the virus has lost ‘strength’ at this stage. We cannot rule out that some lineages will eventually evolve towards to lower symptom severity but this cannot be taken for granted.”
Dr Elisabetta Groppelli, Lecturer in Global Health and virologist at St George’s, University of London, said:
“The suggestion that the virus is weakening is currently not based on established evidence. For that to be the case, we would need to rule out other reasons why it may appear that people are doing better at the moment.
“In Italy, the age of confirmed cases has been steadily decreasing, and we know that disease severity tends to be less in younger groups. Cases are also being diagnosed earlier, which improves outcomes from the disease. Therefore, any evidence that the disease severity is decreasing would need to take these points into account.
“The virus genome is being monitored world-wide, including in the UK. Many universities and research centres are reading the genetic information to assess how much it changes over time and if there is a link between the viral genetic information and the severity of the disease. The consensus so far, is that although the genomes show some changes, there is no evidence for increased or decrease virus features, like transmissibility and disease severity.”
Prof Martin Hibberd, Professor of Emerging Infectious Disease, London School of Hygiene & Tropical Medicine, said:
“Currently there is a world-wide effort to establish if the genetic makeup of SARS-CoV-2 is changing, allowing us to determine if there is any underlying cause of any change in COVID-19 disease. With data from more than 35,000 whole virus genomes, there is currently no evidence that there is any significant difference relating to severity. While this may change in the future, for now it seems likely that there are other reasons why the observed cases look different.
“One explanation for this change in observations might be because of a declining number of cases, where that has been achieved. We know that the virus can infect many (and perhaps the majority) of people without producing any obvious or serious symptoms, while even in those with clear symptoms, 80% have mild disease. During a major outbreak, those mild or inapparent cases are likely to be overlooked. However, in a situation where the numbers of severe cases are falling, there may be time to start observing people with less severe symptoms – giving the impression that the virus is changing.”
Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:
“In the absence of data is difficult to assess the validity of these claims, and I am not aware of any other studies claiming that the virus is weakening”
Dr Oscar MacLean, of the MRC-University of Glasgow Centre for Virus Research, said:
“These claims are not supported by anything in the scientific literature, and also seem fairly implausible on genetic grounds.
“The vast majority of SARS-CoV-2 mutations are extremely rare, and so whilst some infections may be attenuated by certain mutations, they are highly unlikely to be common enough to alter the nature of the virus at a national or global level. We know that susceptibility to the virus significantly differs across age and risk groups, and so infection outcomes will also drastically differ across individuals. As testing efforts are scaled up across the globe, asymptomatic and mild infections which previously would not have been detected, are now much more likely to be identified. It’s important not to confuse this with any weakening on the virus’s part.
“Making these claims on the basis of anecdotal observations from swab tests is dangerous. Whilst weakening of the virus through mutations is theoretically possible, it is not something we should expect, and any claims of this nature would need to be verified in a more systematic way. Without significantly stronger evidence, no one should unnecessarily downplay the danger this highly virulent virus poses, and risk the ongoing society-wide response.”
All our previous output on this subject can be seen at this weblink:
Prof Martin Hibberd: No conflicts of interest