Molecular Epidemiology and Diversity of SARS-CoV-2 in Ethiopia, 2020-2022 (preprint)

Ethiopia is the second most populous country in Africa and the sixth most affected by COVID-19 on the continent. Despite having experienced five infection waves, >499 000 cases, and ~7 500 COVID-19-related deaths as of January 2023, there is still no detailed genomic epidemiological report on the introduction and spread of SARS-CoV-2 in Ethiopia. In this study, we reconstructed and elucidated the COVID-19 epidemic dynamics. Specifically, we investigated the introduction, local transmission, ongoing evolution, and spread of SARS-CoV-2 during the first four infection waves using 353 high-quality near-whole genomes sampled in Ethiopia. Our results show that whereas viral introductions seeded the first wave, subsequent waves were seeded by local transmission. The B.1.480 lineage emerged in the first wave and notably remained in circulation even after the emergence of the Alpha variant. The B.1.480 was out-competed by the Delta variant. Notably, Ethiopia lack of local sequencing capacity was further limited by sporadic, uneven, and insufficient sampling that limited the incorporation of genomic epidemiology in the epidemic public health response in Ethiopia. These results highlight Ethiopia role in SARS-CoV-2 dissemination and the urgent need for balanced, near-real-time genomic sequencing.

Global Expansion of SARS-CoV-2 Variants of Concern: Dispersal Patterns and Influence of Air Travel (preprint)

In many regions of the world, the Alpha, Beta and Gamma SARS-CoV-2 Variants of Concern (VOCs) co-circulated during 2020-21 and fueled waves of infections. During 2021, these variants were almost completely displaced by the Delta variant, causing a third wave of infections worldwide. This phenomenon of global viral lineage displacement was observed again in late 2021, when the Omicron variant disseminated globally. In this study, we use phylogenetic and phylogeographic methods to reconstruct the dispersal patterns of SARS-CoV-2 VOCs worldwide. We find that the source-sink dynamics of SARS-CoV-2 varied substantially by VOC, and identify countries that acted as global hubs of variant dissemination, while other countries became regional contributors to the export of specific variants. We demonstrate a declining role of presumed origin countries of VOCs to their global dispersal: we estimate that India contributed <15% of all global exports of Delta to other countries and South Africa <1-2% of all global Omicron exports globally. We further estimate that >80 countries had received introductions of Omicron BA.1 100 days after its inferred date of emergence, compared to just over 25 countries for the Alpha variant. This increased speed of global dissemination was associated with a rebound in air travel volume prior to Omicron emergence in addition to the higher transmissibility of Omicron relative to Alpha. Our study highlights the importance of global and regional hubs in VOC dispersal, and the speed at which highly transmissible variants disseminate through these hubs, even before their detection and characterization through genomic surveillance.

Comparing SARS-CoV-2 sequencing methodologies during early phase detection of the Delta variant in South Africa (preprint)

Background: Genomic surveillance, with the aid of next-generation sequencing (NGS) technologies, revolutionized the SARS-CoV-2 pandemic. Coupled with high-performance analysis software, methodologies such as the Ion Torrent S5 and Illumina MiSeq dramatically improved the genomic surveillance capacity within South Africa during the height of the pandemic. Using de-identified remnant samples collected from Eastern Cape and analysis software, Genome Detective and NextClade, we compared the sequencing process, genomic coverage, quantification of mutations, and clade classification from sequence data generated by these two common “benchtop” NGS platforms. Results: Sequence data analysis revealed success rates of 175/183 (96%) and 172/183 (94%) on the Ion Torrent S5 and Illumina MiSeq, respectively. Internal quality metrics were assessed in terms of genomic coverage (>80%) and the number of mutations identified (<100). A greater number of higher-genomic coverage sequences were generated on the Ion Torrent S5 (99%) than on the Illumina MiSeq (80%) and <100 mutations was obtained by both platforms. Ion Torrent S5 generated high coverage sequences from samples having a broader range of viral loads (VL) compared to the Illumina MiSeq, which was less successful in sequencing samples with lower viral loads. Clade assignments were comparable across platforms which accurately differentiated between Beta (<45%) and Delta (≤30%) VOCs. A disparity in clade assignment was observed in <10% of sequences due to poor coverage obtained on the Illumina MiSeq, followed by a failure rate of ≤6% across the two platforms. Manual library preparation found both methods similar in terms of sample processing, handling of larger sample quantities, and clade assignment for SARS-CoV-2. Variability between the Ion Torrent S5 and Illumina MiSeq was observed in sequencing run duration (3,5 hrs vs 36 hrs), sequencing process (semi-automation vs manual), genomic coverage (99% vs 80%), and viral load requirements (broad range vs high VL). Conclusion: The Illumina MiSeq and Ion Torrent S5 are both reliable platforms capable of performing WGS with the use of amplicons and providing specific, accurate, and high throughput analysis of the SARS-CoV-2 whole viral genomes. Both sequencing platforms are feasible platforms for the genomic surveillance of SARS-CoV-2, each with its specific advantages and trade-offs.

Continued Emergence and Evolution of Omicron in South Africa: New BA.4 and BA.5 lineages (preprint)

South Africa's fourth COVID-19 wave was driven predominantly by three lineages (BA.1, BA.2 and BA.3) of the SARS-CoV-2 Omicron variant of concern. We have now identified two new lineages, BA.4 and BA.5. The spike proteins of BA.4 and BA.5 are identical, and comparable to BA.2 except for the addition of 69-70del, L452R, F486V and the wild type amino acid at Q493. The 69-70 deletion in spike allows these lineages to be identified by the proxy marker of S-gene target failure with the TaqPath COVID-19 qPCR assay. BA.4 and BA.5 have rapidly replaced BA.2, reaching more than 50% of sequenced cases in South Africa from the first week of April 2022 onwards. Using a multinomial logistic regression model, we estimate growth advantages for BA.4 and BA.5 of 0.08 (95% CI: 0.07 - 0.09) and 0.12 (95% CI: 0.09 - 0.15) per day respectively over BA.2 in South Africa.

Omicron sub-lineages BA.4/BA.5 escape BA.1 infection elicited neutralizing immunity (preprint)

The SARS-CoV-2 Omicron (B.1.1.529) variant first emerged as the BA.1 sub-lineage, with extensive escape from neutralizing immunity elicited by previous infection with other variants, vaccines, or combinations of both. Two new sub-lineages, BA.4 and BA.5, are now emerging in South Africa with changes relative to BA.1, including L452R and F486V mutations in the spike receptor binding domain. We isolated live BA.4 and BA.5 viruses and tested them against neutralizing immunity elicited to BA.1 infection in participants who were Omicron/BA.1 infected but unvaccinated (n=24) and participants vaccinated with Pfizer BNT162b2 or Johnson and Johnson Ad26.CoV.2S with breakthrough Omicron/BA.1 infection (n=15). In unvaccinated individuals, FRNT50, the inverse of the dilution for 50% neutralization, declined from 275 for BA.1 to 36 for BA.4 and 37 for BA.5, a 7.6 and 7.5-fold drop, respectively. In vaccinated BA.1 breakthroughs, FRNT50 declined from 507 for BA.1 to 158 for BA.4 (3.2-fold) and 198 for BA.5 (2.6-fold). Absolute BA.4 and BA.5 neutralization levels were about 5-fold higher in this group versus unvaccinated BA.1 infected participants. The observed escape of BA.4 and BA.5 from BA.1 elicited immunity is more moderate than of BA.1 against previous immunity. However, the low absolute neutralization levels for BA.4 and BA.5, particularly in the unvaccinated group, are unlikely to protect well against symptomatic infection. This may indicate that, based on neutralization escape, BA.4 and BA.5 have potential to result in a new infection wave.

Selection analysis identifies unusual clustered mutational changes in Omicron lineage BA.1 that likely impact Spike function (preprint)

Among the 30 non-synonymous nucleotide substitutions in the Omicron S-gene are 13 that have only rarely been seen in other SARS-CoV-2 sequences. These mutations cluster within three functionally important regions of the S-gene at sites that will likely impact (i) interactions between subunits of the Spike trimer and the predisposition of subunits to shift from down to up configurations, (ii) interactions of Spike with ACE2 receptors, and (iii) the priming of Spike for membrane fusion. We show here that, based on both the rarity of these 13 mutations in intrapatient sequencing reads and patterns of selection at the codon sites where the mutations occur in SARS-CoV-2 and related sarbecoviruses, prior to the emergence of Omicron the mutations would have been predicted to decrease the fitness of any virus within which they occurred. We further propose that the mutations in each of the three clusters therefore cooperatively interact to both mitigate their individual fitness costs, and, in combination with other mutations, adaptively alter the function of Spike. Given the evident epidemic growth advantages of Omicron over all previously known SARS-CoV-2 lineages, it is crucial to determine both how such complex and highly adaptive mutation constellations were assembled within the Omicron S-gene, and why, despite unprecedented global genomic surveillance efforts, the early stages of this assembly process went completely undetected.

SARS-CoV-2 Genetic diversity and lineage dynamics of in Egypt (preprint)

COVID-19 was first diagnosed in Egypt on 14 February 2020. By the end of November 2021, over 333,840 cases and 18,832 deaths had been reported. As part of national genomic surveillance, 1,027 SARS-CoV-2 near whole-genomes had been generated and published by the end of May 2021. Here we describe the genomic epidemiology of SARS-CoV-2 in Egypt over this period using a subset of 976 high-quality Egyptian genomes analysed together with a representative set of global sequences within a phylogenetic framework. We show that a single lineage, C.36, introduced early in the pandemic was responsible for most cases in Egypt. Furthermore, we show that to remain dominant in the face of mounting immunity from previous infection and vaccination, this lineage evolved into various sub-lineages acquiring several mutations known to confer adaptive advantage and pathogenic properties. These results highlight the value of continuous genomic surveillance in regions where VOCs are not predominant and enforcement of public health measures to prevent expansion of existing lineages.

Rapid epidemic expansion of the SARS-CoV-2 Omicron variant in southern Africa (preprint)

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemic in southern Africa has been characterised by three distinct waves. The first was associated with a mix of SARS-CoV-2 lineages, whilst the second and third waves were driven by the Beta and Delta variants respectively. In November 2021, genomic surveillance teams in South Africa and Botswana detected a new SARS-CoV-2 variant associated with a rapid resurgence of infections in Gauteng Province, South Africa. Within three days of the first genome being uploaded, it was designated a variant of concern (Omicron) by the World Health Organization and, within three weeks, had been identified in 87 countries. The Omicron variant is exceptional for carrying over 30 mutations in the spike glycoprotein, predicted to influence antibody neutralization and spike function4. Here, we describe the genomic profile and early transmission dynamics of Omicron, highlighting the rapid spread in regions with high levels of population immunity.

SARS-CoV-2 Omicron has extensive but incomplete escape of Pfizer BNT162b2 elicited neutralization and requires ACE2 for infection (preprint)

The emergence of the SARS-CoV-2 Omicron variant, first identified in South Africa, may compromise the ability of vaccine and previous infection (1) elicited immunity to protect against new infection. Here we investigated whether Omicron escapes antibody neutralization elicited by the Pfizer BNT162b2 mRNA vaccine in people who were vaccinated only or vaccinated and previously infected. We also investigated whether the virus still requires binding to the ACE2 receptor to infect cells. We isolated and sequence confirmed live Omicron virus from an infected person in South Africa. We then compared neutralization of this virus relative to an ancestral SARS-CoV-2 strain with the D614G mutation. Neutralization was by blood plasma from South African BNT162b2 vaccinated individuals. We observed that Omicron still required the ACE2 receptor to infect but had extensive escape of Pfizer elicited neutralization. However, 5 out of 6 of the previously infected, Pfizer vaccinated individuals, all of them with high neutralization of D614G virus, showed residual neutralization at levels expected to confer protection from infection and severe disease (2). While vaccine effectiveness against Omicron is still to be determined, these data support the notion that high neutralization capacity elicited by a combination of infection and vaccination, and possibly by boosting, could maintain reasonable effectiveness against Omicron. If neutralization capacity is lower or wanes with time, protection against infection is likely to be low. However, protection against severe disease, requiring lower neutralization levels and involving T cell immunity, would likely be maintained.

Rapid replacement of the Beta variant by the Delta variant in South Africa (preprint)

The Beta variant of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in South Africa in late 2020 and rapidly became the dominant variant, causing over 95% of infections in the country during and after the second epidemic wave. Here we show rapid replacement of the Beta variant by the Delta variant, a highly transmissible variant of concern (VOC) that emerged in India and subsequently spread around the world. The Delta variant was imported to South Africa primarily from India, spread rapidly in large monophyletic clusters to all provinces, and became dominant within three months of introduction. This was associated with a resurgence in community transmission, leading to a third wave which was associated with a high number of deaths. We estimated a growth advantage for the Delta variant in South Africa of 0.089 (95% confidence interval [CI] 0.084-0.093) per day which corresponds to a transmission advantage of 46% (95% CI 44-48) compared to the Beta variant. These data provide additional support for the increased transmissibility of the Delta variant relative to other VOC and highlight how dynamic shifts in the distribution of variants contribute to the ongoing public health threat.

The continuous evolution of SARS-CoV-2 in South Africa: a new lineage with rapid accumulation of mutations of concern and global detection (preprint)

Global genomic surveillance of SARS-CoV-2 has identified variants associated with increased transmissibility, neutralization resistance and disease severity. Here we report the emergence of the PANGO lineage C.1.2, detected at low prevalence in South Africa and eleven other countries. The emergence of C.1.2, associated with a high substitution rate, includes changes within the spike protein that have been associated with increased transmissibility or reduced neutralization sensitivity in SARS-CoV-2 VOC/VOIs. Like Beta and Delta, C.1.2 shows significantly reduced neutralization sensitivity to plasma from vaccinees and individuals infected with the ancestral D614G virus. In contrast, convalescent donors infected with either Beta or Delta showed high plasma neutralization against C.1.2. These functional data suggest that vaccine efficacy against C.1.2 will be equivalent to Beta and Delta, and that prior infection with either Beta or Delta will likely offer protection against C.1.2.