The aim of the “Sentinel” national surveillance program is to monitor the circulating respiratory viruses, including SARS-CoV-2 variants, and hence underpin public health actions.
In week 14/2021, the overall frequency of the SARS-CoV-2 B.1.1.7 variant in all samples sequenced increased to 81,4% (CI 78,4% – 84,4%, p<0,05). For the SARS-CoV-2 B.1.351 variant, we found an overall frequency of 14,2% (CI 11,5% – 16,9%, p<0,05) within the sequenced samples and for P.1, 1,25% (CI 0,4% – 2,1%, p<0,05).
The representative sample was estimated, based on the number of positive cases in Luxembourg for week 14 (1265). The minimum sample size required to detect prevalence of B.1.1.7 (75%) reported in week 13, with an error margin of 5%, was estimated to be 235 specimens. This number corresponds to a coverage of 18,6 %, which exceeds the minimum coverage recommended by ECDC (10%). The sequencing results of week 14 are representative of the circulating variants in Luxembourg with a margin of error of 5%.
The total number of sequences performed this week was 661, with 641 specimens having been collected in the time frame of week 14/2021. The sequencing coverage this week was 50,7% from all positive cases in Luxembourg.
The “Sentinel” surveillance network reported 102 consultations in week 14 (05/APR/2021 – 11/APR/2021). There was no case of ILI1, as shown in Figure 1. The number of consultations for ARI2 was 15, which represents 15% of consultations.
Patients presenting with ILI and ARI at the Covid Consultation Centre (CCC) in Luxembourg were tested using a respiratory virus panel (ADV = Adenovirus, FLU A = Influenza A, FLU B = Influenza B, HRV = Human Rhinovirus, MPV = Human metapneumovirus, PIV = Parainfluenza virus, RSV = Respiratory Syncytial Virus, SARS-CoV-2 = Severe acute respiratory syndrome coronavirus 2).
The SARS-COV-2 was the most prevalent respiratory virus detected in the “Sentinel” network, with 92 positive cases (32%). The wave of Human Rhinovirus (HRV) continued in week 14/2021, with 13 positive cases in 289 tests (4,4%). Sporadic cases of other respiratory viruses continued to appear, such as 8 cases of PIV (2,8%), 4 cases of MPV and 1 case of RSV. No case of Influenza A/B was detected. (c.f. Figure 2).
In Luxembourg, we have tested 289 samples from the Sentinel surveillance network, as compared to 948 specimens tested in Europe, in the week 14/2021. Two of these 948 specimens tested positive for Influenza type A virus. Influenza activity remained at interseasonal levels.(Source: FluNews Europe).
The National Reference Laboratory for Acute Respiratory Infections at LNS continues to improve the representativeness of the pool of sequenced specimens to reach real-time epidemiology, by implementing the following weekly sequencing activities:
The representative sequencing sample was based on the minimum number of specimens required to extrapolate prevalence of VOC variants with error rate of 5%. The representative sample was estimated based on the number of positive cases in Luxembourg for week 14 (1265). The minimum sample size required to detect prevalence of B.1.1.7 (75%) with an error margin of 5% was estimated to be 235 specimens. The calculation was based on a sample size calculation tool that uses the expected prevalence of the variant in the total population. (Population Proportion – Sample Size – Select Statistical Consultants (select-statistics.co.uk). This number represented a coverage of 18,6% which exceeds the minimum coverage recommended by ECDC (10%). The number of non-targeted specimens of Luxembourgish residents sequenced this week was 565. Therefore, our sequencing results this week are representative of the circulating variants in Luxembourg.
The starting material used for sequencing is respiratory specimens (nasopharyngeal or oropharyngeal swabs) that have already been tested positive by RT PCR.
The LNS sequencing data sharing strategy includes sharing of the sequencing data with GISAID EpiCov database (www.gisaid.org ) on a periodic basis.
Last week the microbial genomics platform at the LNS sequenced 661 specimens, with 641 collected in week 14/2021. This represents 50,7% of the new infections reported in Luxembourg in week 14/2021. Among the 641 specimens, 28 specimens were reported to be part of a cluster or outbreak investigation, and 48 specimens were from non-residents. This leads to 565 specimens, collected in week 14, and being the representative population sequencing sample. In the population representative sample of residents, the frequency of B.1.1.7 and B.1.135 was 81,4% and 14,2% respectively.
The population sequencing coverage in week 14/2021 was 50,7% (Figure 3). Based on statistical inference, the frequency of the reported variants in week 14/2021 is representative of the circulating variants in Luxembourg with a margin of error of 5%.
Lineages (variants) have been assigned based on Rambaut et al by means of Phylogenetic Assignment of Named Global Outbeak LINeages (pangolin) software (v2.3.6, pangoLEARN version 2021-03-29).
The lineage nomenclature system that we use is the one proposed by Rambaut et al. that focuses on actively circulating virus lineages (https://cov-lineages.org ).
In week 14/2021, in the population representative sample, after removal of cluster samples, and excluding specimens collected from non-residents, there were 13 circulating SARS-CoV-2 variants, with the main three variants being B.1.1.7 (81,4%, CI 78,4% – 84,4%) followed by B.1.351 (14,2%, CI 11,5% – 16,9%) and P.1 (1,25% , CI 0,4% – 2,1%), as shown in Figure 4.
Among specimens collected within the week 14/2021, 522 cases of the B.1.1.7 variant have been detected, representing 81,4% of the specimens in the week’s sequencing pool (by comparison, the week 13/2021 pool had shown a frequency of 75,5% of this variant, including additional specimens having been sequenced from previous weeks). The total case count of sequenced variant B.1.1.7 was 3028 by week 14/2021. The earliest collection date for this variant remains 19/DEC/2020 and the latest is 11/APR/2021.
In the collection period of week 14/2021, 91 cases of the South African variant B.1.351 have been detected, representing 14,2% of the specimens in the week’s sequencing pool (by comparison, the week 13/2021 pool had shown 17,7% of this variant, including additional specimens having been sequenced from previous weeks). The total case count of sequenced variant B.1.351 was 734 by week 14/2021. The earliest collection date for this variant remains 11/JAN/2021 and the latest is 11/APR/2021.
In week 14/2021 two additional cases of B.1.525 and 8 new cases of the Brazilian variant P.1 have been detected. Thus, the case count by week 14 for B.1.525 is 5 (latest sampling date 07/APR/2021) and for P.1, 17 cases (latest sampling date 10/APR/2021).
By now, no case of A.23.1 has been detected in Luxembourg (Figure 5).
Lineage B.1.1.7 is characterized by several spike protein mutations, including N501Y, H69/V70del and P861H. The variant seems to have a considerable epidemiological impact, as it has a higher transmissibility rate.
Lineage B.1.351 holds numerous spike protein mutations, of which three are located in the receptor binding domain (K417N, E484K and N501Y), and are therefore relevant for antibody binding. As for B.1.1.7, a higher transmissibility rate and viral loads seem to be associated with this variant. Due to the K417N and E484K mutations, an impact on vaccination efficacy and possibility of reinfection is subject to scientific investigation.
Lineage P.1 (descendent of B.1.1.28), initially found in the Amazon region, has a similar mutation profile as the South African variant, including E484K and N501Y. Concerns are, as for the South African variant, higher transmissibility and a decreased protection by neutralizing antibodies.
Lineage B.1.525 carries several mutations of biological significance, including E484K, Q677H and F888L. It does not carry N501Y, but a set of deletions similar to the B.1.1.7 variant.
Currently the LNS genomic surveillance program – independently from lineage calling – notes the occurrence of 13 different known SARS-CoV-2 mutations, assumed to have clinical and epidemiological relevance. The list of observed mutations is being updated continually, based on the appearance and prevalence of SARS-CoV-2 variants.
The following table provides the overall frequencies of these mutations, detected in the lineage-assignable genome sequences, analyzed between 01/SEP/2020 and 11/APR/2021 (N=8251), as well as the frequencies in week 14/2021.
Genomic sequencing of SARS-CoV-2. A guide to implementation for maximum impact on public health. WHO, 8 January 2021.
COVID-19 data portal. 2020 (https://www.covid19dataportal.org/sequences )
J Hadfield et al. Nextstrain: real-time tracking of pathogen evolution. Bioinformatics 2018;34:4121-4123
A Rambaut et al. A dynamic nomenclature proposal for SARS-CoV-2 lineages to assist genomic epidemiology. Nat Microbiol 2020;5:1403-1407