Genomic Evolution of SARS-CoV-2 Variants

The genomic evolution of SARS-CoV-2 is driven by a balance of random mutation, natural selection and genetic drift as the virus spreads through human populations. Its RNA genome accumulates single-nucleotide changes and small insertions or deletions, which may alter the spike glycoprotein, polymerase and other functional elements. Periods of rapid global expansion have been punctuated by the emergence of variants bearing combinations of substitutions that enhance transmissibility, alter antigenicity or confer replication advantages. Transmission bottlenecks are generally narrow, limiting the diversity passed between hosts, whereas prolonged or repeated infections can allow minor variants to rise to dominance. Continuous genomic surveillance underpins vaccine updates, informs public health measures and improves our understanding of how host factors and immune pressure shape the virus’s evolutionary trajectory.

Research from Nature Portfolio

Recent studies have demonstrated that transmission events of both early and highly transmissible lineages are characterised by tight bottlenecks, often involving just one to three virions establishing new infections. Comparative sequencing of households infected with Alpha, Delta and Omicron showed that most intra-host populations carried zero or one detectable variant at the point of transmission, suggesting limited opportunity for novel mutations to spread in acute chains. A separate investigation of a well-traced Delta outbreak reported exceptionally high viral loads early in infection—approximately a thousand-fold greater than ancestral lineages—and similarly narrow transmission bottlenecks. Yet minor intra-host variants were observed to transmit on occasion, contributing directly to substitutions fixed at the population level during rapid spread.

Genomic Evolution of SARS-CoV-2 Variants publication trend

The graph below shows the total number of articles in genomic evolution of sars-cov-2 variants across all publications each year (not limited to Nature Index journals).

Technical terms

Single-nucleotide variant (SNV): A change of one nucleotide base in the viral genome.

Intra-host variant (iSNV): A genetic variant present at low frequency within a single infected individual.

Transmission bottleneck: The reduction in viral population diversity when a new host is infected by a subset of virions.

Codon adaptation index (CAI): A measure of how closely viral codon usage matches that of the host, affecting protein expression.

Viral lineage: A genetically distinct branch in the phylogenetic tree defined by shared mutations.

References

1. Rapid transmission and tight bottlenecks constrain the evolution of highly transmissible SARS-CoV-2 variants. Nature Communications (2023).
2. SARS-CoV-2 within-host diversity and transmission. Science (2021).
3. Viral infection and transmission in a large, well-traced outbreak caused by the SARS-CoV-2 Delta variant. Nature Communications (2022).
4. Optimization and Deoptimization of Codons in SARS‐CoV‐2 and Related Implications for Vaccine Development. Advanced Science (2023).
5. SARS-CoV-2 population dynamics in immunocompetent individuals in a closed transmission chain shows genomic diversity over the course of infection. Genome Medicine (2024).
6. The P323L substitution in the SARS-CoV-2 polymerase (NSP12) confers a selective advantage during infection. Genome Biology (2023).