There Probably Aren't Different Strains of SARS-CoV-2 (Yet)

TL;DR

As of May 12, 2020, experts lacked strong evidence that any SARS-CoV-2 lineage behaved differently enough to count as a distinct strain. The virus was mutating at less than half the rate of flu, and sequencing revealed traceable lineages such as D and G, but genetic patterns alone could not establish greater transmissibility or virulence. Read on to understand what lineages reveal, and why experiments and peer review remain essential.

Transcript

This episode was filmed on May 12th, 2020. If we have more recent episodes about the COVID-19 pandemic, we’ll include them in the description. Every year, we need to make a new flu vaccine. That’s because there are multiple strains of the flu, and that one most likely to become a problem changes from year to year. SARS-CoV-2, the virus that causes ... Read More

Key Insights

• 😳 SARS-CoV-2 is mutating at a slower rate than the flu virus.
• ❓ Mutations in the virus can provide insight into its origins and transmission patterns.
• ❓ The impact of specific mutations on the virus's behavior and virulence is still uncertain.
• ❓ Different lineages of SARS-CoV-2 may have originated from different regions.
• ❓ Studies on mutations and lineages should undergo peer review for validation.
• ❓ Functional significance cannot be determined solely by genetic sequencing.
• ☠️ Vaccines developed for SARS-CoV-2 may remain effective for a significant period due to the virus's relatively slow mutation rate.

Questions & Answers

Q: Were there different strains of SARS-CoV-2 as of May 12, 2020?

Experts did not have strong enough evidence to classify any branch of the SARS-CoV-2 family tree as a new strain. Distinct lineages could be identified through genetic sequencing, but researchers had not shown that they behaved differently enough to qualify as separate strains.

Q: What does “strain” mean when discussing SARS-CoV-2?

A strain generally means an evolutionary lineage that has accumulated enough mutations to behave differently from related viruses. That difference might involve infecting a new species or spreading faster, but there is no strict genome-percentage threshold in the term’s definition.

Q: How quickly was SARS-CoV-2 mutating compared with flu?

Analysis of a shared database indicated that SARS-CoV-2 was mutating relatively slowly, at less than half the rate of flu. Mutations were still occurring and could be used to trace viral lineages.

Q: How can scientists track SARS-CoV-2 lineages?

Scientists sequence and compare virus samples collected from patients. Differences between their genomes allow researchers to follow lineages over time and infer where those lineages may have originated.

Q: What were the D and G lineages of SARS-CoV-2?

A mid-April paper reported that West Coast samples tended to encode aspartic acid at one genomic position, while East Coast samples tended to encode glycine there. The resulting lineages were called D and G, based on the single-letter codes for those amino acids.

Q: What did the D and G lineages suggest about how SARS-CoV-2 reached the United States?

Following the genetic changes suggested that SARS-CoV-2 entered the United States multiple times. The first West Coast cases were thought to be linked to China, while many early East Coast cases may have been more closely linked to Europe.

Q: Did the D-to-G mutation make SARS-CoV-2 more transmissible or virulent?

The transcript says no firm conclusion could be drawn. Although the mutation affects the spike protein and studies proposed effects on transmissibility or virulence, other scientists disagreed, and genetic sequence data alone could not establish the mutation’s functional significance.

Q: Why were experiments and peer review needed to evaluate SARS-CoV-2 mutations?

A mutation’s sequence does not reveal by itself how it changes viral behavior, and patterns of spread can also reflect public-health measures or coincidence. Experiments specifically designed to test function were therefore necessary, while peer review could identify mistakes or shortcomings in preliminary preprints.

Summary & Key Takeaways

• Every year, a new flu vaccine is needed due to multiple strains of the flu. Scientists are studying if SARS-CoV-2, the virus that causes COVID-19, is also developing into different strains.

• SARS-CoV-2 is mutating relatively slowly compared to the flu, but mutations are still happening. By studying these mutations, scientists can track how different lineages of the virus spread over time.

• There are distinct lineages of SARS-CoV-2, but it is unclear if these lineages act differently from each other. The mutations could potentially impact the virus's ability to infect or cause damage, but more research is needed to understand the functional significance.