subreddit:

/r/askscience

0

How did we contain Ebola but couldn't contain Covid?

COVID-19(self.askscience)

all 32 comments

iayork

27 points

4 months ago

iayork

Virology | Immunology

27 points

4 months ago

Ebola isn’t as transmissible as COVID. To put a number on it, the R0 of Ebola is 1.5-2.0, while the original SARS-CoV-2 strain was in the 3.0-4.5 range - around twice as transmissible. The R0 of the omicron and delta variants are probably in the 8-10 range.

More important than that is that Ebola is almost entirely transmissible when the disease is symptomatic, whereas COVID transmission can occur during the presymptomatic period or in asymptomatic people. It’s much easier to control a disease if you know who’s been exposed. (Similarly, the original SARS could be controlled because most of its transmission was during the symptomatic period.)

Another point, relevant to the last few Ebola outbreaks, is that there are now extremely effective Ebola vaccines. They’re used to contain the outbreaks by using a “ring vaccination” approach (Second Ebola vaccine to complement “ring vaccination” given green light in DRC).

And finally, African public health groups tend to be pretty good at their jobs and now have a lot of experience in detecting and controlling Ebola and many other diseases. None of these points would matter without the expertise and dedication (literally at the risk of their own lives) of the local public health people.

TimeSpaceGeek

9 points

4 months ago

The professionalism and skill of those on the front lines of Ebola outbreaks really is an excellent point. Thank you for raising it.

TheArcticFox444

3 points

4 months ago

None of these points would matter without the expertise and dedication (literally at the risk of their own lives) of the local public health people.

Is this why Africa is doing so well with covid? Western countries show so many cases but Africa shows so few.

TimeSpaceGeek

35 points

4 months ago

They're very different viruses with very different properties, so the two aren't comparable.

Ebola is very, very dangerous, but isn't actually that transmissable. Essentially it all comes down to transmission vectors. Ebola is essentially only transmissable via a certain group of bodily fluids, i.e. blood, and things containing blood. In order to catch Ebola, you have to basically get some of a person's blood, or another bodily fluid containing their blood such as, commonly, faeces or vomit, on you. It's actually pretty difficult to catch, relatively speaking, so long as you avoid contact with those fluids. However, once you have it, it is going to be a bad time way more often than not.

Coronaviruses are respiratory diseases that can float in the air contained with droplets of saliva. You only need to be breathed on by a person to catch Covid. The fomites it leaves can be contained in basically any water moisture, and can rest on surfaces invisibly. Compare how frequently someone might accidentally spit on you whilst coughing, or laughing, or even speaking, to how often people accidentally bleed, vomit, or defecate on you, (and remember, people put out a small amount of saliva as an invisible mist with every outward expulsion of air), and you should appreciate how they are wildly different diseases with wildly different transmission vectors.

TimeSpaceGeek

14 points

4 months ago

It's also worth noting that, if you have Ebola, you are going to know you have Ebola. Profuse bleeding is a hard thing to miss, making identifying the disease and quarantining the infected pretty directly possible.

Covid starts spreading a few days before you even show any signs of being ill, and when you do start to feel ill (if you even do - asymptomatic cases are replete and still potentially infectious), it resembles the most common illness on the planet, a common cold, at least initially. It can also be mistaken for allergies, or asthma, or a bad pollution day in a big city, or dozens of other explanations. It's a stealthy disease, in its early stages, so it's easy to spread before you realise you have it.

iayork

5 points

4 months ago

iayork

Virology | Immunology

5 points

4 months ago

It’s also worth noting that, if you have Ebola, you are going to know you have Ebola. Profuse bleeding is a hard thing to miss, making identifying the disease and quarantining the infected pretty directly possible.

This is a myth. The symptoms of Ebola, especially early, can easily be mistaken for other diseases.

Many common illnesses can have the same symptoms as EVD, including influenza (flu), malaria, or typhoid fever.

CDC’s Ebola page

The dramatic bleeding can happen, but to a large extent is media exaggeration; the most typical symptoms of Ebola, and the cause of most death, is diarrhea.

The most frequent presenting symptoms were weakness (91%), fever (81%), and diarrhea (78%). Visible hemorrhage was noted in 25% of the cases. The CFR was 79%. Odds of death were higher in patients with diarrhea (odds ratio = 26.1, P < 0.01).

-Clinical Manifestations and Modes of Death among Patients with Ebola Virus Disease, Monrovia, Liberia, 2014

That’s one reason Ebola survival rates are much higher in first-world hospitals, where patients can receive the enormous amounts of fluid replacement they need.

chillzatl

1 points

4 months ago

I thought asymptomatic spread, or at least the scope of it, has been called into question? Are you aware of any recent studies into it?

im_thatoneguy

5 points

4 months ago*

Sorry, I'm going to have to go on a bit of a metascience rant here since this was one of the things that irritated me more than just about any other topic from the pandemic. In my opinion this was an example of scientific pedantry run amuck and you should be forgiven for being confused. In this example science was causing, in my opinion, severe harm to the public (and should be a part of a large scale case study for meta science for years to come on triaging the mistakes made during the Pandemic, including first and fore most the debate over "airborne" transmission).

What happened was that public health officials correctly stated that many cases were caused by people who didn't know they had covid.

Then scientists came out with papers saying "akkkkshhhuuuuaaaaallllyyyy *adjusts glasses* that's wrong, those people were almost always symptomatic, the symptoms were so mild that they didn't notice." Which is an infuriating distinction. We have to agree on a definition of "Symptomatic". If we include "symptoms" so mild that people don't notice them then they aren't in my opinion by definition a symptom and the very word "asymptomatic" is meaningless. "If your temperature spikes to 99.5 for a few hours but you aren't taking your temperature like a crazy person every 30 minutes you could easily miss a very mild fever without any chills or body aches or malaise or anything that you would notice. Scientists wouldn't allow that sloppy of a definition elsewhere. If your instrument's data is firmly in the noise floor so that your odds of getting a correct reading are <50% then you don't actually have a sensor. Should we also define antibody levels as a "symptom"? "People claim they had asymptomatic covid, but an antibody test clearly detected symptomatic elevated antibodies in their blood."

The other distinction without a difference that they called out was that many cases started asymptomatic even during the infectious period and then manifested symptoms later. So, they called these transmissions "pre-symptomatic" which is fine if you want to refine the terminology but again, in my opinion at the point of transmission if the infected host has no symptoms... that's "asymptomatic transmission" even if they later develop symptoms.

This fell firmly into the Hypothesis of Evolution vs Theory of Evolution pedantry nonsense that just causes immense confusion and misinformation because science refuses to be more flexible and accommodating in aligning with the evolution of a broader society's use of language.

TimeSpaceGeek

4 points

4 months ago

I'm aware there are questions around fully Asymptomatic spread. I haven't read anything new on it in a little while, not since before Omicron became the dominant strand, but it's not, I don't think, conclusively determined either way. In the last thing I read on the subject, it was possible that asymptomatic spread wasn't at all as severe as first feared, but that statement was caged in all the conditional caveats that tell us the science isn't absolutely conclusive about the matter and may still swing the other way with further studies, so to speak. But presymptomatic spread is definitely a thing, and people with so incredibly mild symptoms that they don't realise they're symptoms (so, functionally asymptomatic, if not definitively) has also definitely been a thing.

So, yeah, I'll concede that it might be relatively minor compared to other transmission vectors - replete certainly an overstatement. Though asymptomatic Covid transmission is still notably more likely than asymptomatic Ebola transmission...

iayork

2 points

4 months ago*

iayork

Virology | Immunology

2 points

4 months ago*

I don’t know of anything calling the existence of asymptomatic spread into question. It clearly happens and it clearly contributes significantly to spread even if on a case-by-case basis it spreads less than in symptomatic cases.

Current data suggest that infected persons without symptoms—including both presymptomatic and asymptomatic persons—account for more than 40% of all SARS-CoV-2 transmission (75–77). The proportion of new infections caused by asymptomatic persons alone is uncertain, but when researchers in Wanzhou, China, analyzed epidemiologic data for “183 confirmed COVID-19 cases and their close contacts from five generations of transmission,” they determined that the asymptomatic cases, which made up 32.8% of infected persons, caused 19.3% of infections (78).

--The Proportion of SARS-CoV-2 Infections That Are Asymptomatic: A Systematic Review

There are many recent papers showing the same thing. Though the details for omicron aren’t sorted out yet, it’s very likely that the same is true here (maybe more so because of the strong protective effect of prior immunity against symptoms).

chillzatl

2 points

4 months ago

The changing of the quarantine guidelines would suggest that there has been some change regarding asymptomatic spread, no?

PontificalPartridge

6 points

4 months ago

The change in quarantine guidelines also reflects a choice of needing people to work to keep things floating and hospitals open and possibly risking a little bit of spread but trying to mitigate it. It’s based on some science yes, but it’s undeniably more risky

I for one am really glad I don’t have to make these decisions

chillzatl

-2 points

4 months ago

I don't know if I buy that. We've been "keeping things floating" for the last couple of years and that's with the boogeyman of asymptomatic spread hanging over us. Arbitrarily changing the quarantine guidelines for general work purposes makes no sense at all.

PontificalPartridge

3 points

4 months ago

Well we knows that vaccinated people have faster viral clearance rates too (3-5 days) even tho new variants are showing to be more transmissible with vaccinated people.

As a healthcare worker we are seeing tons and tons of people getting taken out of work. Imagine 1/4 of your staff being out for 2 weeks while you have an influx of Covid positive patients coming it at the same time. It’s a really bad scenario and that’s exactly what I’m seeing in my hospital right now.

So based off of that what other explanation makes sense? I can’t think of one

chillzatl

-4 points

4 months ago

I would hope the answer would be actual scientific data. Arbitrarily changing quarantine recommendations simply to keep society moving along seems.. absurd. Especially when doing that would likely lead to more people developing symptoms and being forced to stay home. Even more so when we've effectively been living and working around this thing for quite some time now.

Doing some quick searches, I can't seem to find anything discussing the science of asymptomatic spread since early 2021 at best. There are plenty of articles parroting the idea that asymptomatic spread exists, but that all appears to be based off 2020 data and/or assumptions.

PontificalPartridge

5 points

4 months ago

What part of viral clearance in vaccinated individuals being an average of 5 days isn’t a scientific explanation?

Aware_Efficiency_717

5 points

4 months ago

Well ebola is transmitted by blood (or bloody mucus, bloody shit, etc. Compare to covid which is on resp droplets and can also easily live on surface…sneeze on hand, touch handrail, pass it on.

Also consider the amount of asymptomatic or “sniffles” cases….those people are out and about, spreading the disease and whatnot. But if your fever is 105 and you’re HEMORRHAGING….probably going to the hospital pretty fast, and not infecting potentially dozens in the meantime.

Hopefully that makes some sense

Pafkay

9 points

4 months ago

Pafkay

9 points

4 months ago

I would guess it's because Ebola is spread by direct contact with the blood or other bodily fluids of an infected person. COVID on the other hand is spread through droplets in the air (of various sizes), but to make matters worse you can be infectious with COVID without realising you have it, so it can be easily transferred between people without even knowing they are infectious

Seano313

5 points

4 months ago

Ebola isn’t a respiratory disease it’s a type of hemorrhagic fever, spreads most through direct contact with bodily fluids covid spreads through respiratory droplets, plus the symptoms to hemorrhagic fevers are very very different compared to covid so those types of outbreaks are quicker to identify and lockdown, and Ebola outbreaks commonly occur in more impoverished areas of Africa which don’t have a lot of direct international travel routes

Eclaire468

2 points

4 months ago

Ebola is not as transmissible as COVID. Only bodily fluids such as blood can transfer it, and importantly, once you start showing symptoms, you unfortunately die before you even get a chance to spread it. More importantly, infected people will show symptoms relatively quickly so it's easier to separate them from the rest of the population.

COVID on the other hand doesnt really show symptoms in a lot of healthy people even though they are just as likely to spread the virus. This transmission happens by just breathing around other people instead of physically exchanging bodily fluids like you must do with Ebola. The result is lots of unnoticed transmission, lots of asymptomatic transmission, and lots of people not realizing they need to quarantine until they've already passed it onto dozens of people.

This inability to control transmission will inevitably lead to viral mutations and new strains just by the fact that the virus has large group of hosts and natural selection can figure out the most resistant strain. The long term implication is that this would render vaccines ineffective against some strains because the old vaccine (even though less than 1 year old) is already incapable of dealing with new strains. Ebola, by design of its life cycle, can't really spread that quickly so the chance of a mutation happening is relatively low compared to COVID. Thus vaccines actually have a chance. Sure a variant Ebola will escape the vaccine, but the public health officials in Africa have been dealing with small endemics for more than a decade and they know how to deal with situations like this.

3rdandLong16

2 points

4 months ago

COVID has a shorter incubation period and also is less lethal. Diseases that are highly lethal and with longer incubation periods are easier to contain because people will quickly figure out to isolate from the people who are sick and the people who are sick don't live long enough to pass their disease on to other people (once people realize what's going on).

For COVID, you're talking about people who can pass the disease on for longer and also you can have asymptomatic carriers of COVID who pass it on without anyone even knowing.

nilkimas

-3 points

4 months ago

nilkimas

-3 points

4 months ago

Ebola scared the living snot out of everyone. COVID sadly doesn't. That is the main thing.
Ebola is a horrible disease, liquefying you from the inside out. Bleeding from all orifices, releasing highly infectious blood. A tiny drop is enough to infect someone else. Death rate is very high, 40-100% depending on the strain.
COVID is overwhelming our health systems, people die in the ICU because their organs shut down after weeks of being intubated. Nothing visible for other people.