Old 03-22-2020, 04:28 AM
RivkahChaya's Avatar
RivkahChaya is offline
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Two Strains?

The "two-strain" theory.

I have read this theory of covic-19 in a couple of places that are very respectable, and since this is exactly the way smallpox worked, I don't think it's impossible.

The idea is that there are two major strains of Covid-19: one is pretty deadly, and one is very mild. Age and general health are still factors in whether you live or not, but another major factor is the strain you have. When you hear in the same day of a young person dying, and an elderly person living, they likely had different strains. IIRC, the death rate of variola major was 90%, but the death rate of variola minor was only about 20%. And since V. minor left people healthy enough to be up and about, V. minor spread more rapidly.

For a long time, the very similar disease vaccinia (cowpox) was used to inoculate against variola-- but one the difference was discovered, the inoculation was done with variola minor.

IANAD, but as I understand it, the smallpox vaccine worked by giving the recipient a smallpox infection of the skin, using an the mild strain. It would be fought off with little lasting effects other than the distinctive scar, because smallpox doesn't become systemic when it enters the skin, but we develop antibodies all the same.

If researchers can successfully isolate the minor strain, that may be 1/2 way toward developing a vaccine.
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Old 03-22-2020, 08:20 AM
Ulysses is offline
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I’m skeptical until there is further evidence. My understanding is that the two-strain hypothesis is based primarily on a recent article published in the National Science Review in early March. Link here:


I’m not an epidemiologist, public health expert, or related professional. As such, I’d be keenly interested in hearing opinions on the article from those with expertise, who are in a better place to assess the science.

That said, I do have some experience in research oversight and I’m reluctant to rely on a single article. A key question is verification: i.e., would other researchers reach similar conclusions? This is especially a concern here because there is a potential for research bias. The authors are all based at Chinese universities and labs. As such, they may have a bias that favors blaming the high COVID-19 fatality rate in China on “two strains” rather than acknowledging China may have failed to timely react and may have a high population of people who are malnourished, immuno-compromised, exposed to rampant air pollution, or otherwise at elevated risk, and that China’s medical infrastructure is lacking.

Have you seen the two-strain hypothesis supported in other sources? News moves so fast that I may have missed it.
Old 03-22-2020, 09:00 AM
Stranger On A Train is offline
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Even if there are two distinct strains of the SARS-CoV-2 virus, it is not guaranteed that exposure to and the development of antibodies against one strain will convey immunity against the other any more than exposure to one strain of influenza will immunize you against all others. Nor is it guaranteed that exposure or vaccination will provide indefinite immunity.

Vaccine development is complex and coronaviruses in particular are sufficiently mutable that a universal vaccine may be elusive. This is why it is important to focus on both treatments to retard development of the COVID-19 disease and more reliable testing to detect and intervene patients early in infection, as well as non-pharmaceutical measures (social distancing, better sanitation, public health surveillance) to combat outbreaks.

Old 03-22-2020, 09:36 AM
Wesley Clark's Avatar
Wesley Clark is offline
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This article says there are two strains, but there is no difference in symptoms or lethality due to it.


When Xiaolu Tang at Peking University in Beijing and colleagues studied the viral genome taken from 103 cases, they found common mutations at two locations on the genome. The team identified two types of the virus based on differences in the genome at these two regions: 72 were considered to be the “L-type” and 29 were classed “S-type”.

A separate analysis by the team suggests that the L-type was derived from the older S-type. The first strain is likely to have emerged around the time the virus jumped from animals to humans. The second emerged soon after that, says the team. Both are involved in the current global outbreak. The fact that the L-type is more prevalent suggests that it is “more aggressive” than the S-type, the team say


The differences between the two identified strains are tiny. In fact, they can’t really be considered to be separate “strains”, says Jones. And many of the genetic differences won’t affect the production of proteins, and so won’t change the way the virus works, or the symptoms it causes, he says. One is not more deadly than the other.
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Old 03-22-2020, 11:26 AM
Stranger On A Train is offline
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Originally Posted by Wesley Clark View Post
This article says there are two strains, but there is no difference in symptoms or lethality due to it.

Take any authoritative statements you read, even from legitimate sources, with a grain of salt. There just isn’t enough epidemiological data to make any definitive assessments about the virulence of separate strains. And viruses mutate regularly, so although unlikely a previously innocuous strain could suddenly become more virulent.

Old 03-22-2020, 10:39 AM
Carryon is offline
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Posts: 927
Some of this comes from past epidemics. Which usually happens in a flu type epidemic is people with the mild strain go about their business.

People with the severe strain, stay home. They get better or die off. Thus they don't spread the deadlier form.

Thus overtime the mild strain becomes mainstream.

This was the opposite in the Spanish flu, where the mild strain infected stayed in the trenches and the front lines, while the severely infected were transported in crowded trains to hospitals thus spreading the more deadly version.


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