1. Is it possible to get COVID-19 twice?

No, doesn't seem to be, but you might still have "viral shedding" for a bit even after you are "recovered". meaning you could still be contagious.

4. There's evidence that there are multiple strains, can you get both strains?

You shouldn't think about them as multiple strains, as of now it is 1 disease.

5. What's the likelihood that a mutation will occur once treatment is more widespread?

Mutations occur all the time, there are already 10's of known mutations of virus, it doesn't mean there are 10 separate diseases.

6. Does the heat make it significantly less likely for you to get COVID-19?

There's some evidence warm weather slows spread for viruses like this, but we can't assume that about this virus yet. A good counterpoint is Qatar adding 258 cases in one day, it's hot there.

"it's hot [in Qatar]."

I used to live in that part of the world. Air conditioning and active cooling is pervasive there. In a sense, people's exposure to the overwhelming heat of the day is perhaps much more limited than you might expect.

There are surprisingly few cases in Africa (https://www.newscientist.com/article/2236760-we-dont-know-wh...) and Africa is a poorer continent in general, and perhaps aircon is much more limited there than that area of Arabia. Maybe there's a link.

Africa generally being a poorer continent also means a lot less travel to spread the disease, especially international travel from Asia and Europe, and the potential for local outbreaks to pass unnoticed due to lack of medical care, especially if symptoms for most young people are benign, and elderly people dying at the first sign of infection is a common occurrence

There could be less testing in Africa, so less confirmed cases. Here in New Zealand we have had only 5 cases with no increase in days, yet very close links to China and Australia and cool fall weather, making me wonder if and how many undiagnosed cases there are.

Best papers I've seen on the weather - virus link so far

https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3551767

https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3550308

The case fatality rate is estimated at 2% - 3% but that is with medical care. Without ventilators and ICU care, CFR might rise to as high as 10%-15%. With its exponential growth rate, it'd be highly surprising for the virus to go unnoticed so long.

I saw different numbers, ~0.6% with good medical care(SK), 2-4% with poor medical care (Early stages in China).

According to the Johns Hopkins doctor recently interviewed by Sam Harris (sorry, couldn’t find the name) the South Korean number is likely the more accurate one due to a higher prevalence of testing. The higher rates from other countries are essentially a denominator problem (I.e., with limited tests only the most sick are tested, leaving the only moderately sick untested and thus out of the calculation)

I've seen an infographic passed along, albeit on twitter, so authenticity is suspect --but it was comparing ages in SK and Italy of cases, where mortality is higher in Italy, because mean age was higher in Italy, a lot of the tests in SK were in churches where initial outbreaks were that were prevalently populated by youth...

2000x 20 year olds 2000x 60 year olds...and you're gonna have highly different results for CFR.

I'd say it's somewhere in the middle of both... maybe something like 1.5. But I'm not an epidemiologist, but if the age gaps matter then it could be about that... just my thoughts.

Do you have a source for the '10%-15%' value? If not, I'd encourage you to not spread FUD.

That's the estimated percentage of people who need some form of ICU treatment due to COVID-19. If there's no more ICU beds left, it's safe to assume that the majority of people in need of ICU treatment that can't get it will die.

You also have to add all the other patologies that will get affected by the lack of ICUs. All in all, 10% is a safe estimate. That's why flattening the curve is extremely important. The actual percentage in need of ICU will surely vary with time, but that's the important metric, because that's how many people will die when the health system saturates.

5% needing ITU was initial estimate. In Italy it’s 10% due to an elderly population. And some on ITU would survive without ITU but it does improve chances. You make good points, I’m mostly just saying there is a high degree of uncertainty

Multiple sources indicate that’s the severe percentage, and we know a bit about untreated ards.

Moreover, deaths from lack of capacity will not be limited to covid cases. And many of the current non-covid icu cases may be exposed to medical staff who are not being tested (in the USA) and die that way. This is what happens in nursing facilities like Seattle.

Italy is the first Nation that lost control of the virus and can't get infected into icu. Just look at their numbers for a real world example.

Yes, look at their numbers: more than 5000 ICU beds (and more being added) and less than 1000 in use.

https://www.linkiesta.it/it/article/2020/03/11/italia-corona...

https://www.washingtonpost.com/world/europe/italy-coronaviru...

https://www.newnotizie.it/2020/03/12/coronavirus-posti-letto...

the ramp up isn't done, nor halfway yet, as italy hasn't reached inflection of the exponential curve yet. once the net new cases begins to steadily decrease the numbers are roughly half way to the final max.

But AC is very common in the US too. So shouldn't we expect spread in US summer to behave more like Qatar than Africa? Europe on the other hand may slow down since I think AC hasn't caught on to the same extent.

It depends on the part of the US you live in. In Florida (where I am from) air conditioning is common. In Boston its only common in offices.

If he reduces spread, it will be helpful on the margin and may help flatten the curve

Demographics structure. E.g. in Nigeria 65+ old constitute ~3% of population, in Italy ~22%. Now compare that with COVID-19 severity and mortality age breakdown.

Source: https://www.cia.gov/library/publications/the-world-factbook/...

I thought that the reason cold weather helps the spread is the higher humidity means the water droplets you spray last longer.

Air conditioning tends to produce a very dry environment which should also cause the droplets to evaporate very quickly.

Cold weather weakens your immune system.

Also cold weather has lower humidity.

>> 5. What's the likelihood that a mutation will occur once treatment is more widespread?

> Mutations occur all the time, there are already 10's of known mutations of virus, it doesn't mean there are 10 separate diseases.

I agree, but I'd like to add more details. Most mutations are irrelevant, and if you have antibodies for the original version, the same antibody is useful for the new version.

From time to time, the mutation is in the part that encodes the part that is recognized by the antibody, and then you may be infected by the new version.

[There are a lot of other mutations. A lot of mutations just make the virus not able to reproduce, or break some important part, so the mutated version just disappear. Another mutations make the virus more effective or less effective, so they change how bad the symptoms are.]

Others may change how fatal the infection is (in either direction)

This is actually one of the reasons that viruses generally become less deadly the longer they circulate through a population. A less-deadly version will spread faster (by not killing it's hosts), and will tend to outcompete a deadlier version

Flu viruses don’t spread less when it’s warm. They spread less when it’s more humid.

For the northern hemisphere it’s much less humid in winter, but that’s not true everywhere.

https://www.livescience.com/27533-flu-transmission-humidity....

We really should be increasing humidity in hospitals and offices in the winter. Newer planes have already been moving in that direction (to increase comfort).

Careful. You are correct, but incomplete. It is ABSOLUTE humidity which matters, not relative humidity.

Absolute humidity (the amount of water in the air) is low in winter because cold air doesn't hold as much moisture.

Relative humidity does not depend on temperature since it is a ratio of the absolute humidity to the max absolute humidity at the given temperature.

> It is ABSOLUTE humidity which matters, not relative humidity.

This 2019 paper says that (i) in higher relative humidity, the fine droplets stay larger (larger size after evaporation down to the equilibrium size, given by Kelvin equation) and thus linger in the air for a shorter time. And (ii) higher temperatures, virus proteins denaturate a bit faster. The compound effect of higher relative humidity and higher temperature then makes it look like it correlates to higher absolute humidity.

https://royalsocietypublishing.org/doi/full/10.1098/rsif.201...

Not sure how relevant it is, but influenza (flu) and common coronaviruses (common cold) are not in the same family. Anyways, it seems like it is not a good idea to speculate, even the viruses have closely related:

https://ccdd.hsph.harvard.edu/will-covid-19-go-away-on-its-o...

Also, spreading of flu during "flu season" is marked by holidays when long distance travel happens. This causes slightly different strains of the flu to be brought into regions where people do not have a natural defense to that strain.

Interesting tidbit I learned at a Town Meeting (streamed) yesterday. Winter Break in Massachusetts was instituted to halt the rapid spread of flu during the winter months. Kids would take it into school, spread it among themselves and bring it home to adults, who would get hit harder by it.

The winter break put an an incidental isolation in place that slowed the person-to-person spread down.

This is why schools have to close now to control the spread of COVID-19.

I think you mean February break.

Winter break usually refers to the break that includes Christmas and New Years Day.

In Massachusetts they instituted a second break in February, in addition to spring break in April, in order to cut the flu season.

There is a lot of long distance traveling during summer as well, with all the vacations.

I believe the flu virus is susceptible to UV exposure which may correlate to warmer weather?

As explained to me by an M.D. this is why flu infections go down in the summer

Hospitals worry about many microorganisms besides the coronavirus. It would be unwise to encourage the growth of bacteria and fungi to arrest one virus that can be controlled in other ways.

Some places have humid summers and dry winters, and others have more humid winters and dry summers, like the west coast of the US.

Flu always seems to be during the winter though.

Vitamin D deficiency in winter, close quarters are factors.

From my experience, I have always gotten the flu, or some kind of sickness, after the cold months, as it turns into spring and summer.

When a warmer spring month rolls around, I think that I must’ve escaped getting sick with the flu, then, bam!, I get hit with it, and get knocked out for a few days.

The annoying flu is during the summer, when it’s hot, and you’re sick, so you just become more miserable.

As per this paper - https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3551767. Both increase in temperature and humidity reduces the transmission of COVID-19.

Abstract: This paper investigates how air temperature and humidity influence the transmission of COVID-19. After estimating the serial interval of COVID-19 from 105 pairs of the virus carrier and the infected, we calculate the daily effective reproductive number, R, for each of all 100 Chinese cities with more than 40 cases. Using the daily R values from January 21 to 23, 2020 as proxies of non-intervened transmission intensity, we find, under a linear regression framework for 100 Chinese cities, high temperature and high relative humidity significantly reduce the transmission of COVID-19, respectively, even after controlling for population density and GDP per capita of cities. One degree Celsius increase in temperature and one percent increase in relative humidity lower R by 0.0383 and 0.0224, respectively. This result is consistent with the fact that the high temperature and high humidity significantly reduce the transmission of influenza. It indicates that the arrival of summer and rainy season in the northern hemisphere can effectively reduce the transmission of the COVID-19.

Related HN thread: https://news.ycombinator.com/item?id=22563932

Doctors tend to be reluctant to extrapolate strong conclusions from relatively close R0 values like those presented because of the number of confounding factors. It’s really most valuable when looking at orders of magnitude difference (e.g., measles with an R0 of around 15 compared to seasonal flu with an R0 of around 1-3).

I didn’t see in that study much consideration of other variables and the p-value used for relative humidity was on the high side by publication standards (up to 10%)

Regarding Quatar (or any warm/hot place): Note that a significant fraction of people spends a lot of time inside. This means the temperature there is actually colder, there's less sunlight (especially UV), and people are closer to each other. Also note that for the common cold, the reason that it spreads more during winter times is not primarily temperature, but the fact that people spend more time inside while ventilating (opening windows) less often.

Comparing speed of distribution in different countries is extremely difficult, as there are too many factors at play. The 258 cases in Qatar might have been 500 if it was colder there, no one can proof or refute that.

> The 258 cases in Qatar might have been 500 if it was colder there, no one can proof or refute that.

It certainly means hot weather won’t “stop” the virus, just slow it by (in your example) 50%. That’s not a lot of comfort, although it would buy some time.

I wonder?

I know that in places like Qatar and India, there is a tendency to use artificial cooling. (I'm pretty sure India is the single biggest growth market for air conditioning on the planet.) I'm just thinking, if a bunch of people gather in an air conditioned theater, would it even matter if it was 95 degrees outside? Just a thought.

I guess to really know, we'd have to wait and see what happens in places where it is hot, and humid, and artificial cooling is not so widespread? Like Sub-Saharan Africa.

> 6. Does the heat make it significantly less likely for you to get COVID-19?

There is actually another part of the world where it's summer. Australia's case count graph is displaying the standard hockey stick shape, so based on the typical growth rate we should know in a week or two.

Can you cite some sources for your responses to 1 and 4? Re: 5, there's clearly a distinction between typical mutations, which have no particular effect on the virus' behavior but do allow us to trace infections, and behavioral mutations, which might allow reinfection or make the virus more or less contagious or deadly. I think GP is asking about the second kind, since they're also asking about reinfection. Maybe that's obvious, but considering that, are there sources saying that the evidence so far is that there is only one strain?

Re 6: this is an interesting question. My layman's understanding is that heat usually reduces the spread of disease in temperate climates both because the disease can't survive as well and because people spend more time outdoors and in less people-dense spaces. In somewhere really hot like Qatar, we would expect to see the opposite of the second effect; I'd think people would spend more time indoors with A/C when it's excessively hot outside, increasing transmission rates as the outside temperature rises.

Also Brazil: cases are starting to exponentially grow, and it's summer there and super hot. Even hotter cities like Brasilia are having cases.

Is Qatar hot and dry? I think heat with humidity are more likely to dampen the spread compared to just heat

> I think heat with humidity are more likely to dampen the spread compared to just heat

That's odd to me because I associate warm and wet with uncleanliness and festering cesspools.

This outbreak has made me realise how I've gone my whole adult life without knowing some basic things about bacteria and viruses. Like, I never knew about how soap dissolves the virus's outer coating...

Anyway apparently hot and wet is good for bacteria, but cold is better for viruses. The bit that made it click for me is that viruses aren't metabolising anything outside of the host-cell, so the best a virus can hope for is to not be destroyed -- and cold is a better preservative.

I'm still not sure whether hot and humid is better than hot and dry though? I think I read that hot and dry is worse, because it increases evaporation.

> I never knew about how soap dissolves the virus's outer coating

That's not true for every type of virus, but it is true for corona viruses.

Humidity makes flu less contagious, likely because something about the wet heavy air deactivates airborne viruses.

https://www.google.com/amp/s/www.livescience.com/amp/27533-f...

Welcome to living anywhere near the great lakes in summertime.

Qatar is more humid than people think for being a desert country, because it is a peninsula in the gulf. As I write this, it's about 70% relative humidity.

Dunno about Qatar but in Abu Dhabi humidity has reached 100%

Relative

While there is evidence that viruses don't like heat, the main argument about wanting to flatten the peak until the warmer months is because the colder months also have correlation to other diseases.

This disease would spread the same in any weather but most countries would be able to cope better, hospitals have more space and people's immune systems would be stronger in the summer.

> A good counterpoint is Qatar adding 258 cases in one day, it's hot there.

Not this week. Temperature is below 30° celsius, more around 20°. Summer has yet to come.

(Not a doctor.) In general it is possible to get the same infection twice, depending on circumstances like a weak immune system, not recovering properly after the first one etc. Whether this is true for ncov is most likely not scientifically proven yet, but even if, it is safe to assume that this happening is the exception.

All I've heard regarding #1 thus far is "we don't know". Do you have source that states otherwise? Based on the responses so far, I'm not alone in wanting to review it.

Here are some of the mutations / strains [1]

[1] - https://nextstrain.org/ncov

If it's mutating, would it be better to get the virus early, before it mutates to something more severe?

Mutating doesn't mean it's going to get worse. It's entirely possible for the virus to mutate into a less dangerous form. Going out of your way to get it now is too much of a risk.

While I don't believe SARS-CoV-2 is quite as bad as the media frenzy is making it out to be, it's absolutely a good idea to do everything you can to avoid getting it. The same goes for the flu and for colds. If you catch any of these, you may be OK, but you risk spreading it to people who won't be.

1-3% case fatality rate? 70% of the population expected to be infected.

That's ~1 out of every 100 people. This isn't just a media frenzy, by the end of this you WILL know someone who died as a result of (complications of) Coronavirus.

And yet a lot of countries seem to have controlled it to a great extent. China, South Korea, japan, Singapore. They’re not showing explosive numbers.

They're not reporting explosive numbers...

Other that for China, do you have any evidence the numbers are doctored?

Especially South Korea, which has been very transparent and done a ton of testing.

In Italy, the numbers are closer to 7%

But its hard to believe they report infection rate properly. It may be 7% of those with symptoms (arriving at hospital)? Which is expected to be a 'cherry picked' subset and have a higher rate.

Typically viruses mutates to less severe variants because it allows them to infect more people.

I think this is true for very lethal viruses that have risk of killing host before spreading.

For virus that can spread before any symptoms and long after symptoms disappear and survive so long on the objects and in the air I think there will be no evolutionary pressure to get milder.

And we can get harsher version just by random chance because this virus is so infectious that it has a lot of leniency whether and when to kill the host.

selective pressure should favor mutating to something not worse as the worse ones get more notice, avoidance and the hosts don't last as long.

It's also still Spring-ish in Qatar, so not quite as hot as it can get.

Do high humidity levels decrease potency in case of Coronavirus?

You will not find concrete answers online because this is a research area, scientists are not sure yet about how to answer these questions. And sometimes the existing answers are based on limited information or just misinformation.

And this disease is still very new. There are too many unique cases and difference between cases that it's almost impossible to take any conclusion.

There is no good evidence that there are different strains.

That Chinese paper suggesting two strains has been withdrawn for lack of evidence.

Enveloped Coronaviruses have RNA proofreading mechanisms to lessen mutations, so it is unlikely there are multiple strains.

The "two strains" rumor was debunked on episode 590 of the This Week in Virology podcast.

I've posted a transcript of the relevant portion here: [1]

[1] - https://news.ycombinator.com/item?id=22564199

Australia has a current outbreak that seems to be progressing the same way it does in every other country. It's summer there.

If your immune system develops an antibody based on epitopes that differ in the second strain, I would think you could contract it again. Two people who overcome a virus may ultimately derive different antibodies, and some may do better at matching the class of viruses than others.

I don't think it's very common to be that unlucky in your own body's development of a suitable antibody.

At least, this is my understanding based on a recent microbiology course I took. Immune response is a fantastically complex thing.

Viral reinfection is a known thing. Immunology is just, well, really complicated. One person's antibodies may have worked against the same virus their family member's did, but not against some slightly mutated strain that arrives after circulating for a month. Or frankly, testing isn't perfect and it's possible he had the flu before and never had COVID-19 at all.

In general, populations as a whole develop herd immunity to viruses reasonably quickly. This process is understood. Individual case data is always crazy.

So: 1. Sometimes, 2. Probably, 3. Yes, 4. Maybe, 5. It'll definitely happen eventually, 6. Yes, almost certainly.

And indeed, it will never go away, just like H1N1 flus have continued to circulate ever since the 1918 pandemic. But after a while, immune response and vaccination regimes will turn it into a nuisance.

> Is it possible to get COVID-19 twice?

Is it truly "twice", is my question.

Or is it just the same event, lasting longer than expected.

Its only been around a few months so hasn't had a chance to significantly mutate- and it hasn't needed to. As such its unlikely you'll get a second time any time soon, however in future years it could mutate.

Here is an article on how they can see the DNA changing in different patients so can track the path of infections. https://bedford.io/blog/ncov-cryptic-transmission/

There are two different strains already.

No, that paper was heavily criticised and then retracted.

I don't think we're talking about the same thing.

There is very little known about this particular case - for instance what testing procedure were they using. It could be that the first test gave a false negative, or the second a false positive.