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Comment by akg_67 | Hacker News Reader

Based on the difference in virulence of the virus in Western Europe and US versus Asia, it is hard to believe there is only one strain of SARS-CoV-2.

My hypothesis is that while Asia was originally infected by Wuhan originated strain, the Western Europe and US may have been infected by a mutated strain. The differences in impact in different countries is very difficult to explain without the hypothesis of multiple strains.

Edit: There was a decent article recently (I am unable to find now, most probably from NYT, WSJ) that addressed several factors mentioned in replies and showed none of those could explain the discrepancy in cases across countries. For example, high temperature and warm weather don’t explain differences in cases between Singapore, Thailand, Indonesia, Malaysia, and Amazon region of Brazil.

The closest article, I could find using google search is from Brookings.

https://www.brookings.edu/blog/future-development/2020/05/05...

View on HN

Not sure what you mean. The differences in impact seems to be trivial to explain given the vastly different measures taken by different countries, and their timing relative to the start of the outbreak. The IFR estimates are very similar everywhere.

That would not explain the difference in outcomes between countries with well known cross-contamination. For example, the pandemic spread to Romania from Italy and Spain (there are around 1 million Romanian nationals living in Italy and 3 million in Spain, and constantly traveling between the 3 countries), and yet CFR and R0 are significantly different between them. The difference with Bulgaria is even more stark.

The reality is that government measures seem to have had the biggest impact by far. Western Europe and the US have badly dropped the ball on this issue, whereas Asian and Eastern European nations have mostly handled this much better for their citizens.

Respiratory viruses are very seasonal. Weather conditions matter. Generally speaking temperature, moisture and sun UV radiation decrease the spread of the virus.

Closer to equator you go, less there is seasonal forcing in respiratory viruses.

Could you elaborate on this? How do the effects differ and couldn't a lot of it be explained by the vastly different pandemic reactions (lock-down vs doing almost nothing)?

Because there are too many wildly differing reactions in similar populations.

More than 700 passengers on the Diamond Princess were infected, leading to a total of eight deaths. This would have been an older-than-usual cohort, simply by dint of demographics on cruise ships.

Meanwhile, in New York, deaths in long-term care homes have approached 5,000.

Obviously nursing home residents are a more vulnerable population, but with this kind of disparity in outcomes, I'm not buying it. Nursing homes may have an older clientele, but then, cruise ships aren't staffed by medical professionals.

IMHO it's been obvious that there are multiple strains in circulation for a long time. Otherwise, the medical community needs to explain exactly why outcomes vary so dramatically, not only from one individual to the next, but between populations with similar demographics. When they explain that, then I'll be more interested in their opinions regarding how many strains are out there. If they think the bugs are all the same, they aren't looking closely enough.

Disclaimer: I assume by impact you mean "case fatality rate" (CFR)

This is my hypothesis of lower impact. Both India & Germany have low CFR and we find that in Germany 49% of cases are under the age of 50, while in India 70% of cases are under the age of 50 years. On the contrary, in Italy 70% of Covid infected individuals are above the age of 50, with 39% above the age of 70 and Spain has 69% of cases above the age of 50 with 37% above the age of 70. US case data by age is grouped somewhat differently by CDC but my guess is that close to 40% of infections are in the age-group below 50 years and about 20% are above the age of 70 years, this might partially explain the relatively lower CFR because CFR for ages under 50 is ~0.4% if you are in the age-group of 40-49 & lower below. Median age of the population for these countries are India - 28, Italy - 46, Spain - 44, Germany - 48 & US - 38. Germany seems to have either done something differently here.

This can only partially explain the differences but would be an important factor when looking at overall fatalities.

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