ABSTRACT
Sublineage BA.5 of the SARS-CoV-2 Omicron variant rapidly spread and replaced BA.2 in July 2022 in Tokyo. A high viral load can be a possible cause of high transmissibility. Therefore, the copy numbers of SARS-CoV-2 in nasopharyngeal swab samples obtained from all patients visiting the hospital where this research was conducted were measured using quantitative polymerase chain reaction (qPCR). Viral genotypes were determined using PCR-based melting curve analysis. Next, whole-genome sequencing was performed using approximately one-fifth of the samples to verify the viral genotypes determined using PCR. Then, the copy numbers of the BA.1, BA.2, and BA.5 cases were compared. Contrary to expectations, the copy numbers of the BA.5 cases (median 4.7 x 104 copies/L, n = 290) were significantly (p = 0.001) lower than those of BA.2 cases (median 1.1 x 105 copies/L, n = 184). There was no significant difference between the BA.5 and BA.1 cases (median, 3.1 x 104 copies/L; n = 215). The results presented here suggest that the increased infectivity of BA.5 is not caused by higher viral loads, but presumably by other factors such as increased affinity to human cell receptors or immune escape due to its L452R mutation.
ABSTRACT
The rapid spread of the Delta variant of SARS-CoV-2 became a serious concern worldwide in summer 2021. We examined the copy number and variant types of all SARS-CoV-2-positive patients who visited our hospital from February to August 2021 using PCR tests. Whole genome sequencing was performed for some samples. The R.1 variant (B.1.1.316) was responsible for most infections in March, replacing the previous variant (B.1.1.214); the Alpha (B.1.1.7) variant caused most infections in April and May; and the Delta variant (B.1.617.2) was the most prevalent in July and August. There was no significant difference in copy numbers among the previous variant cases (n=29, median 3.0x104 copies/L), R.1 variant cases (n=28, 2.1x105 copies/L), Alpha variant cases (n=125, 4.1x105 copies/L), and Delta variant cases (n=106, 2.4x105 copies/L). Patients with Delta variant infection were significantly younger than those infected with R.1 and the previous variants, possibly because many elderly individuals in Tokyo were vaccinated between May and August. There was no significant difference in mortality among the four groups. Our results suggest that the increased infectivity of Delta variant may be caused by factors other than the higher viral loads. Clarifying these factors is important to control the spread of Delta variant infection.
ABSTRACT
BackgroundThe spread of SARS-CoV-2 variants, such as B.1.1.7 and B.1.351, has become a crucial issue worldwide. Therefore, we began testing all patients with COVID-19 for the N501Y and E484K mutations associated with SARS-CoV-2. Study designNasopharyngeal swab samples from 108 patients who visited our hospital between February and April 2021 were analyzed. The samples were analyzed using reverse transcription-polymerase chain reaction with melting curve analysis to detect the N501Y and E484K mutations. A part of the samples were also subjected to whole genome sequencing. Clinical parameters such as mortality and admission to the intensive care unit were analyzed to examine the association between increased disease severity and the E484K mutation. ResultsThe ratio of cases showing the 501N+484K mutation rapidly increased from 8% in February to 46% in March. Whole genome sequencing revealed that the viruses with 501N+484K mutation are R.1 lineage variants. Evidence of increased disease severity related to the R.1 variants were not found. ConclusionsWe found that the R.1 lineage variants rapidly prevailed in Tokyo in March 2021.
