A study carried out by the Children’s Hospital Los Angeles shows a high prevalence of the recent D614G mutation as well as a high level of genetic variation in viral samples taken from children infected with SARS-CoV-2.
As in other studies of the virus, the D614G virus seems to have spread rapidly in the population this summer and was present in 99.3% of samples tested in this study. However, there did not seem to be correlation with severity of disease symptoms.
There did seem to be an association between infection with a strain of the virus known as clade 20C and severe disease, but the researchers caution that this result needs to be confirmed in other studies as the number of patients they tested was small.
Although children are less affected by Covid-19 than other sections of the population, a small number of cases have occurred and this prevalence seems to be increasing. In April, 1.7% of reported U.S. COVID-19 cases were in children, which had increased to 7.7% in August. It is therefore important to assess the impact of the virus on this section of the population.
As reported in the journal Open Forum Infectious Diseases, the researchers sequenced viral samples taken from 141 children between March and June 2020 who had confirmed SARS-CoV-2 infection.
Of the patients included in the study, 94 were of Hispanic ethnicity, 19 had underlying conditions and a total of 14 were admitted to hospital because of COVID-19 symptoms. A higher viral load was seen in patients under the age of 5 and in those with obvious symptoms. Only three cases were considered severe and required ICU admission, but no patients died during the study period.
Although the viral strains in the overall group were a mixture of clades 20A, 20B and 20C, the severe patients all had infections with clade 20C.
“Larger studies will be required to confirm that one subgroup of SARS-CoV-2 leads to worse prognosis,” says Gai, “but this study is a clear example highlighting the importance of examining the genetics of the virus. These are the puzzle pieces that will help us get ahead of this pandemic.”
There has been a lot of speculation about the D614G spike protein mutation, which has rapidly become the most common form of the virus over the summer. The general consensus seems to be that it may have made SARS-CoV-2 more infectious, but so far it has not been linked to increased disease severity.
The researchers estimated a mutation rate of 22.2 substitutions per year in the strains they sequenced with the D614G variant, which they note is higher than the average rate of 13.5 substitutions per year recorded for the non D614G cases in California. They suggest that this mutation may be linked to increased viral mutation rate, but caution that more evidence is needed to make a definite conclusion.
“SARS-CoV-2 is genetically unstable,” says Xiaowu Gai, Ph.D., the Director of Bioinformatics at Children’s Hospital Los Angeles. “We tend to refer to ‘the virus,’ but when we think about the viral genome it’s not a static, single virus but really a collection of the genetic changes in all the viruses within an infected patient.”