What does the B.1.1.7 percent mean?
The B.1.1.7 percent quantifies the percentage of the SARS-CoV-2 RNA that belongs to the B.1.1.7 variant. It reflects the percentage of the current COVID cases caused by the B.1.1.7 variant.
Do you quantify all samples?
Quantifying the percentage of B.1.1.7 is more difficult than detecting the B.1.1.7 RNA. After preliminary R&D, we have established a level of quantification (LOQ) required to reliably quantify the amount of B.1.1.7 in your sample. The LOQ is about 3 times higher than the limit of detection (LOD), 100 copies/mL of SARS-CoV-2 as measured by the N1/N2 assay. If your sample falls above the LOD, but below the LOQ, you would receive the B.1.1.7 detection status, but not the B.1.1.7 quantification.
Why are some samples with high SARS-CoV-2 normalized concentration not quantified?
The decision to quantify the B.1.1.7 percentage relies on the raw SARS-CoV-2 concentration because it requires the physical wastewater sample to contain sufficient virus for the assay to work. Therefore, some samples may have a high normalized concentration but insufficient virus in the raw sample to perform quantification.
Why does the plot show raw SARS-CoV-2 concentration?
The plot shows raw concentration because the LOD and LOQ are based on the raw SARS-CoV-2 concentration. The B.1.1.7 quantification is normalized internally and does not depend on or require the PMMV normalization.
What does a percentage of 0% mean?
A percent of 0 means that B.1.1.7 RNA was not detected in your sample. It does not necessarily mean that B.1.1.7 is absent in your community. It could indicate that the level of B.1.1.7 was insufficient to be detected by our assay.
What does a percentage of 100% mean?
If the reported B.1.1.7 percentage is 100%, that means that we did not detect the non-B.1.1.7 version of the RNA in your sample. It does not necessarily mean that everyone with COVID in your community has B.1.1.7. It could indicate that non-B.1.1.7 SARS-CoV-2 molecules were not present in your sample, or their amount was insufficient to be detected.
How is the B.1.1.7 percentage calculated?
We average the results from the three B.1.1.7 targets to estimate the concentration of B.1.1.7 RNA in the sample. We combine the 3 non-B.1.1.7 targets to estimate the concentration of non-B.1.1.7 SARS-CoV-2 RNA. We calculate a percentage of the B.1.1.7 variant as a ratio of B.1.1.7 RNA to the total RNA (B.1.1.7 + non-B.1.1.7).
What’s the variability in this quantification?
We are working hard to understand the variability of the B.1.1.7 measurements. Our preliminary research shows that the B.1.1.7 assay is more variable than our standard N1/N2 based assay. There are several reasons that make B.1.1.7 measurements more variable:
- B.1.1.7 percentage is a ratio of two qPCR reactions, and hence it is more variable than a single measurement
- B.1.1.7-specific primers are less sensitive than our standard assay due to the design limitations
- The B.1.1.7 protocol uses less RNA than the N1/N2 assay because we have to run more qPCR reactions