2019-2020 coronavirus pandemic (Vaccination 2021 Edition)

[tstorm823]

Assuming acquired immunity, of course. Unfortunately, that's currently in question. Getting the coronavirus once may not actually mean you can't get it again. Also trying to do this without vaccines or quarantine and social distancing measures means that a lot more people have to get sick and die before an equilibrium is achieved. People tend to throw around the phrase "herd immunity" not only without properly understanding what that means in a medical context, but also not realizing that we already have several large-scale examples of what happens when an outbreak is left to burn itself out. Just ask the Native Americans.

An outbreak can't burn itself out without acquired immunity. People recovering and outbreaks receding are both substantial evidence that acquired immunity works with sars-cov-2 the same way as most other viruses. It's not HIV spread by breathing. How long the immunity lasts it's something to question, but the only research I've seen suggest a short duration was a small study done specifically on asymptomatic carriers that only concluded that antibodies were less likely to be detected after 2 months, and larger studies have contradicted that.

 

[Phoenixmgs]

Unless Minnesota has substantially broader immunity to the virus before the current rise, which it should, because it was hit harder beforehand, as evidenced by 60% more deaths per million, in spite of Florida having the highest percent of its population over 65 of any state.

I have little faith in the accuracy of those numbers, I don't expect many other countries to report covid deaths as broadly as the US is. If you see a nation that had roughly the same spike trends as Italy or New York, but they claim to have way fewer deaths per capita, they probably just weren't recording the deaths. Analyzing covid deaths from the perspective of excess deaths over recent years is a method with its own faults, but it is a pretty good proxy for how broadly nations are attributing deaths to covid-19, and places like Belgium or Sweden which are above the US on that list have a close match between their reported deaths and the excess over expected deaths, where much of the rest of Europe is pretty shaky (in the places you can find that data).

And you'd do well to pay attention to the places that are below the US and climbing. Nations that are two months behind aren't comparable yet. It will take a full year before we can see the big picture.

In Minnesota, there's only been one day since the start date of the protests (May 26) that have had more infections. Infections are very much down since the protests. Whereas in Florida, May 30 (earliest day on this chart) saw 870 infections and now there's been a day with nearly 10,000 infections and probably (I don't really feel like doing the math) a 2-week span with 5,000 infections per day. Also, Florida currently has a higher % of the population that has been infected than Minnesota. I don't think any place besides NYC could have an infection rate that would be even close to 10% of the population (adjusted via antibody surveys). So we're talking single digit percentages of the population that has been infected pretty much anywhere. Even a state that has twice the immunity than another state (like 2% vs 4%) is not that much in actuality to slow the spread down significantly just due to immunity. How is Minnesota's infection rate lower after than protests while Florida's rate is over 5x its pre-protest rate if the protests have caused the spike? Because it's really hard to spread the virus outside and the protests or any outdoor activities are very low risk for spreading the virus. The increase in infections is from the indoor congregating of public groups of people without masks.

What developed countries are two months behind the US? For the most part, the US was hit later compared to most. Japan was hit after the US and it's doing better than Florida alone while I'm pretty sure it has even denser population zones and over 10x Florida's population. Florida literally beat Japan's infection total in 2 days. You can do some really basic and common sense things to keep the spread of the virus down and for the most part the US didn't do it to begin with and still isn't doing it and it's pretty sad actually.

 

[Dwarvenhobble]

In Minnesota, there's only been one day since the start date of the protests (May 26) that have had more infections. Infections are very much down since the protests. Whereas in Florida, May 30 (earliest day on this chart) saw 870 infections and now there's been a day with nearly 10,000 infections and probably (I don't really feel like doing the math) a 2-week span with 5,000 infections per day. Also, Florida currently has a higher % of the population that has been infected than Minnesota. I don't think any place besides NYC could have an infection rate that would be even close to 10% of the population (adjusted via antibody surveys). So we're talking single digit percentages of the population that has been infected pretty much anywhere. Even a state that has twice the immunity than another state (like 2% vs 4%) is not that much in actuality to slow the spread down significantly just due to immunity. How is Minnesota's infection rate lower after than protests while Florida's rate is over 5x its pre-protest rate if the protests have caused the spike? Because it's really hard to spread the virus outside and the protests or any outdoor activities are very low risk for spreading the virus. The increase in infections is from the indoor congregating of public groups of people without masks.

What developed countries are two months behind the US? For the most part, the US was hit later compared to most. Japan was hit after the US and it's doing better than Florida alone while I'm pretty sure it has even denser population zones and over 10x Florida's population. Florida literally beat Japan's infection total in 2 days. You can do some really basic and common sense things to keep the spread of the virus down and for the most part the US didn't do it to begin with and still isn't doing it and it's pretty sad actually.

Hasn't Minnesota seen like a 40% or so of it's rental properties end up vacated recently.

Might be worth asking where all those people who left went.

 

[Agema]

Might be worth asking where all those people who left went.

Presumably back to their families. Universities will have shut and moved online for students, and lots of businesses will have paused operations or also moved online, so temporary workers have no reason to be around either. There's no point them paying rent that they don't have to. Potentially rental properties might include some AirBnB, so if there's much tourism in Minnesota, they may have taken a dive in use, too.

 

[tstorm823]

In Minnesota, there's only been one day since the start date of the protests (May 26) that have had more infections. Infections are very much down since the protests. Whereas in Florida, May 30 (earliest day on this chart) saw 870 infections and now there's been a day with nearly 10,000 infections and probably (I don't really feel like doing the math) a 2-week span with 5,000 infections per day. Also, Florida currently has a higher % of the population that has been infected than Minnesota. I don't think any place besides NYC could have an infection rate that would be even close to 10% of the population (adjusted via antibody surveys). So we're talking single digit percentages of the population that has been infected pretty much anywhere. Even a state that has twice the immunity than another state (like 2% vs 4%) is not that much in actuality to slow the spread down significantly just due to immunity. How is Minnesota's infection rate lower after than protests while Florida's rate is over 5x its pre-protest rate if the protests have caused the spike? Because it's really hard to spread the virus outside and the protests or any outdoor activities are very low risk for spreading the virus. The increase in infections is from the indoor congregating of public groups of people without masks.

On May 26th, Minnesota was coming down quickly from a major wave, and that downward trend was promptly stopped in its tracks a week later. That is as significant a change in trajectory as a slow rise turning up into a spike.

And the difference in those small percentages is huge, if you operate under my understanding. So like, where is my 10% coming from. I originally made that estimate based on the Diamond Princess. A bunch of people were trapped on a ship with a brand new virus that can spread asymptomatically and 20% of the ship was infected. If you treat that as a test tube and say roughly everyone on that ship was exposed to the virus, 19.2% of the people on board got infected. I round up to 20%. (Brief aside, I'm making assumptions, I know I'm making assumptions, but making predictions is always about finding the best assumptions and then checking them against reality.) So, imagine for a moment this pans out, and 80% of the population is naturally immune to the virus, that 80% of people can be exposed without being infected. What does that mean? It would mean people are much more easily exposed to the virus but most aren't infected.

Normal assumptions of pandemic spread and heard immunity center around an R value, that is meant to describe how many people an average carrier will pass the infection onto. Herd immunity is then calculated as the necessary percentage of acquired immunity required to make it so that 1 or fewer of those people are susceptible. If each person passes it to multiple people, the pandemic grows. If fewer, the pandemic shrinks. That's calculated as 1-1/R0, where R0 is the R value if nobody has been exposed. Early R0 estimates were around 2.5, which calculates to a necessary 60% infection to reach the point where R=1 based on herd immunity. But that's based on the idea that nobody has been exposed to this virus so everyone is susceptible. One of the "1"s in that equation is the current R value, it just happens to be 1 at the point of herd immunity stopping exponential spread. So the broader equation is %immune = 1 - R/R0. If we make a faux R0* for the theoretical world where everyone is susceptible, call that 2.5 R at the beginning of the pandemic, and calculate based on 80% immunity, we get 80% = 1 - 2.5/R0*, therefore R0* = 12.5. Put that back into the equation as R0 to find herd immunity, 1-1/12.5 = 92%. Pull out the 80%, you're left with 12% of people getting actually infected (and then I round off to 10 because these obviously aren't precise figures, and 12% specifically communicates an inappropriate degree of precision; 10 is also just a really easy number to visualize).

That was all based on assumptions from an early test case of sorts. Let's check that against reality. Well, while other places are currently increasing in cases, New York's trend is staying down. The R value isn't going back above 1. What do serology tests suggest about New York? The city in places got as high as 20%, which would be equivalent to the Diamond Princess, and the state has about a 12% infection rate. We look at Sweden, where it's not right to say they did nothing, but they decided to do medium social distancing measures and hold the course until immunity kicks in. Well, the number of cases did come back down as expected. Based on regular assumptions, they expected like a 50% infection rate to have caused that trend, but then serology tests were coming back with single digit infection rates (and people kind of freaked out). If you go with my assumptions instead, that single digit number makes perfect sense, you don't expect more than 10% infection until the end of the pandemic. Like, it checks out pretty well. Not even I expected my back of the envelope math to pan out this accurately.

So circling way back to the 2%-4% comparison. If I'm accurate, the difference between 2% infection and 4% infection is a 20% decrease in how much people spread to each other. That is a big difference, and can easily be the difference between a state going from R < 1 to R = ~1 like Minnesota corresponding to Florida going from R = ~1 to R > 1 with cases growing exponentially as any R great than 1 does. If those simultaneous flexes correspond to the same timeline of activity, and that activity has largely ended, we should see an unnatural looking return to Florida only slowly increasing and Minnesota should go back to dropping slowly over the next week or two.

 

[Silvanus]

That was all based on assumptions from an early test case of sorts. Let's check that against reality. Well, while other places are currently increasing in cases, New York's trend is staying down. The R value isn't going back above 1. What do serology tests suggest about New York? The city in places got as high as 20%, which would be equivalent to the Diamond Princess, and the state has about a 12% infection rate. We look at Sweden, where it's not right to say they did nothing, but they decided to do medium social distancing measures and hold the course until immunity kicks in. Well, the number of cases did come back down as expected. Based on regular assumptions, they expected like a 50% infection rate to have caused that trend, but then serology tests were coming back with single digit infection rates (and people kind of freaked out). If you go with my assumptions instead, that single digit number makes perfect sense, you don't expect more than 10% infection until the end of the pandemic. Like, it checks out pretty well. Not even I expected my back of the envelope math to pan out this accurately.

The most recent graph I can find-- from 21 June-- shows Sweden's positivity rate at 12+%. It still has a significantly higher mortality rate than its Scandinavian neighbours.

It recorded its highest increase last Wednesday. And the W.H.O. notes that while they've increased testing in Sweden recently, their positivity rate is pretty much unchanged.

 

[tstorm823]

The most recent graph I can find-- from 21 June-- shows Sweden's positivity rate at 12+%. It still has a significantly higher mortality rate than its Scandinavian neighbours.

It recorded its highest increase last Wednesday. And the W.H.O. notes that while they've increased testing in Sweden recently, their positivity rate is pretty much unchanged.

There's no way to look at Sweden's recorded cases as anything other than worthless. They decided not to try to contain it, they also basically decided not to measure it. The graph of their positive tests is basically 1:1 against their graph of total tests. By the time they started to scale up testing in earnest, they were a month and a half beyond the peak number of deaths, which is to say likely two full months after their actual peak in cases. They assuredly spiked in cases in late March to early April, just like the rest of Europe, it just wasn't recorded.

 

[Dwarvenhobble]

Presumably back to their families. Universities will have shut and moved online for students, and lots of businesses will have paused operations or also moved online, so temporary workers have no reason to be around either. There's no point them paying rent that they don't have to. Potentially rental properties might include some AirBnB, so if there's much tourism in Minnesota, they may have taken a dive in use, too.

Yeh but this was only after reports of plans to defund police.

 

[Phoenixmgs]

On May 26th, Minnesota was coming down quickly from a major wave, and that downward trend was promptly stopped in its tracks a week later. That is as significant a change in trajectory as a slow rise turning up into a spike.

So, imagine for a moment this pans out, and 80% of the population is naturally immune to the virus, that 80% of people can be exposed without being infected. What does that mean? It would mean people are much more easily exposed to the virus but most aren't infected.

Increased infections are far more likely to be caused from the state's opening phases than from the protests. If everything else was the same and you only had the protests, then you can attribute the protests to the increases but that's not the case. There's quite a few studies showing it's far far more difficult to spread the virus outside and even more so during the day when the sun is out. Even just opening a small window in a room has major effects. There's tons of articles showing the protests have not caused the spikes in virus infections.

That's one hell of an assumption that 80% of the population is immune. Link me to any expert saying anyone is immune from the virus. If 80% of the population is immune, then the virus would have to have the most ridiculous spread rate ever to be able to spread so fast. With the assumption that it's a new virus and everyone can get it, having 70% of people being infected would create herd immunity. If 80% of people are immune by default, how is this virus spreading in the first place then? Once they found out the virus was on the cruise ship, it wasn't like they did some experiment not telling the passengers and had them continue on normally. They quarantined people in their cabins afterward. There was a major change to passenger behavior that occurred. It's far far more likely that that was the cause of the slowing of the infections and not that it burned through the 20% of the people that could get infected.

 

[tstorm823]

That's one hell of an assumption that 80% of the population is immune. Link me to any expert saying anyone is immune from the virus. If 80% of the population is immune, then the virus would have to have the most ridiculous spread rate ever to be able to spread so fast. With the assumption that it's a new virus and everyone can get it, having 70% of people being infected would create herd immunity. If 80% of people are immune by default, how is this virus spreading in the first place then? Once they found out the virus was on the cruise ship, it wasn't like they did some experiment not telling the passengers and had them continue on normally. They quarantined people in their cabins afterward. There was a major change to passenger behavior that occurred. It's far far more likely that that was the cause of the slowing of the infections and not that it burned through the 20% of the people that could get infected.

It would be a much higher spread rate. I put it at 12.5 in my math, which is high. It's roughly equal to Chicken Pox. With how quickly this traversed the globe, is it really that strange to suggest it's as contagious as chicken pox?

70% infected causing herd immunity isn't a set number. That's what you'd need to stop exponential spread in a virus with an R0 of a little over 3. That's like the common cold. To stop something like chicken pox, you need like 91% immune. To stop measles, you need 94%. It depends on how easily the virus transmits. A virus that can move from person to person through air droplets without the infected person having symptoms for like a week is pretty close to as sneaky as you get, and coughing as a major symptom is the traditional fast track to spreading, and those are the defining characteristics of covid-19. My suggestion is that it's spreading in the first place because each infected person isn't exposing just 2-3 more people to the virus, they're exposing 10-15 on average, but most of those people don't become carriers.

 

[Phoenixmgs]

It would be a much higher spread rate. I put it at 12.5 in my math, which is high. It's roughly equal to Chicken Pox. With how quickly this traversed the globe, is it really that strange to suggest it's as contagious as chicken pox?

70% infected causing herd immunity isn't a set number. That's what you'd need to stop exponential spread in a virus with an R0 of a little over 3. That's like the common cold. To stop something like chicken pox, you need like 91% immune. To stop measles, you need 94%. It depends on how easily the virus transmits. A virus that can move from person to person through air droplets without the infected person having symptoms for like a week is pretty close to as sneaky as you get, and coughing as a major symptom is the traditional fast track to spreading, and those are the defining characteristics of covid-19. My suggestion is that it's spreading in the first place because each infected person isn't exposing just 2-3 more people to the virus, they're exposing 10-15 on average, but most of those people don't become carriers.

Way back before it got to the US, the experts predicted exactly when the virus was going to "pop" here, they've been right on the numbers before. There's been several incidents where people have gathered and well over 20% of the people at the gathering got infected. You're going to have to link to some kind of studies that are saying most people are immune to this because it doesn't make any sense that a new virus to humans would have 80% of the population being immune to it.

 

[lil devils x]

Way back before it got to the US, the experts predicted exactly when the virus was going to "pop" here, they've been right on the numbers before. There's been several incidents where people have gathered and well over 20% of the people at the gathering got infected. You're going to have to link to some kind of studies that are saying most people are immune to this because it doesn't make any sense that a new virus to humans would have 80% of the population being immune to it.

No, they are not immune. There are differences in how easily different SARS-Cov-2 strains are spread. The first strain type A, that began in Guangdong was not as easily spread as the strain that is taking over the world now. The mistake that T-storm and Others have been making is that they are mistakenly trying to compare a less easily spread strain to the more easily spread strains and thinking that somehow the earlier strains being less easily spread meant that people had to be immune to them, it does not.

https://www.washingtonpost.com/science/2020/06/29/coronavirus-mutation-science/?arc404=true

 

[lil devils x]

It would be a much higher spread rate. I put it at 12.5 in my math, which is high. It's roughly equal to Chicken Pox. With how quickly this traversed the globe, is it really that strange to suggest it's as contagious as chicken pox?

70% infected causing herd immunity isn't a set number. That's what you'd need to stop exponential spread in a virus with an R0 of a little over 3. That's like the common cold. To stop something like chicken pox, you need like 91% immune. To stop measles, you need 94%. It depends on how easily the virus transmits. A virus that can move from person to person through air droplets without the infected person having symptoms for like a week is pretty close to as sneaky as you get, and coughing as a major symptom is the traditional fast track to spreading, and those are the defining characteristics of covid-19. My suggestion is that it's spreading in the first place because each infected person isn't exposing just 2-3 more people to the virus, they're exposing 10-15 on average, but most of those people don't become carriers.

We will not even achieve herd immunity with a vaccine if too many people refuse to use it:

Fauci says Covid-19 vaccine may not get US to herd immunity if too many people refuse to get it

Dr. Anthony Fauci says he would "settle" for a Covid-19 vaccine that's 70% to 75% effective, but that this incomplete protection, coupled with the fact that many Americans say they won't get a coronavirus vaccine, makes it "unlikely" that the US will achieve sufficient levels of immunity to...

www.cnn.com

Your assessment that we will achieve herd immunity without a vaccine anytime soon is terribly inaccurate.

 

[Silvanus]

There's no way to look at Sweden's recorded cases as anything other than worthless. They decided not to try to contain it, they also basically decided not to measure it. The graph of their positive tests is basically 1:1 against their graph of total tests. By the time they started to scale up testing in earnest, they were a month and a half beyond the peak number of deaths, which is to say likely two full months after their actual peak in cases. They assuredly spiked in cases in late March to early April, just like the rest of Europe, it just wasn't recorded.

I thought you said you "don't expect more than a 10% infection rate until the end of the pandemic". But they're at 12+, they weren't (and aren't) getting those "single-digit" numbers you were talking about, and you're saying they were higher before.

Besides which, without the adequate data before, the "coming back down" that you're looking to for proof of your hypothesis.... wasn't actually recorded anywhere. You're assuming. How're we to draw any conclusions about acquired immunity from this, when we're any lacking solid data showing a downward trend, and the only limited data we do have shows a high infection rate and a high mortality rate?

 

[tstorm823]

Way back before it got to the US, the experts predicted exactly when the virus was going to "pop" here, they've been right on the numbers before. There's been several incidents where people have gathered and well over 20% of the people at the gathering got infected. You're going to have to link to some kind of studies that are saying most people are immune to this because it doesn't make any sense that a new virus to humans would have 80% of the population being immune to it.

You can have places go over the 20% because it's not a random, evenly spaced group. The concept you're missing is innate immunity. Antibodies are not the human body's only response to viral infection, we have non-specific bodily responses as well. Different people are going to have different levels of innate immune response to different pathogens. In particular with sars-cov-2, children seem to avoid the virus altogether at a relatively high rate.It's not because they have some magical forcefield protecting them, it's because their bodies are axing the virus before it can start reproducing inside of them. If you take like a choir of middle-aged people of similar backgrounds, you don't expect a random 20% of them to be susceptible. It isn't random, they might all have similar results. We know some of who gets sick at higher rates than others, but we don't know the exact mechanism of why.

Your assessment that we will achieve herd immunity without a vaccine anytime soon is terribly inaccurate.

I'll let history determine this one. I'm not advocating major policy changes here, just describing how the outcome might be (probably is) a lot better than people currently expect, and I can wait a few months for that the play out before declaring myself right or wrong.

I thought you said you "don't expect more than a 10% infection rate until the end of the pandemic". But they're at 12+, they weren't (and aren't) getting those "single-digit" numbers you were talking about, and you're saying they were higher before.

Besides which, without the adequate data before, the "coming back down" that you're looking to for proof of your hypothesis.... wasn't actually recorded anywhere. You're assuming. How're we to draw any conclusions about acquired immunity from this, when we're any lacking solid data showing a downward trend, and the only limited data we do have shows a high infection rate and a high mortality rate?

Positivity rate isn't infection rate across the whole population. Positivity rate is the percent of tests that come back positive, but testing is obviously biased towards people who are sick. If you did testing for the virus on a random sample of the population, you'd get a much lower number. There aren't currently 1.2 million infected people in Sweden. Positivity rate of tests also doesn't account for previously infected and recovered individuals. Like, Sweden's positivity rate remaining constant as they ramp up testing doesn't mean they have increasing numbers of sick people, it means they weren't previously even testing all the sick people, much like the US in April.

The testing meant to show total rate of people who had ever been infected is antibody testing, and the last I saw out of Sweden they were at 7.3%. The number is certainly higher by now, as that was like a month ago, but I don't know if any more recent data is available. Regardless that was after the bulk of the deaths had already occurred, so it's not likely to have increased dramatically since then.

 

[Silvanus]

Positivity rate isn't infection rate across the whole population. Positivity rate is the percent of tests that come back positive, but testing is obviously biased towards people who are sick. If you did testing for the virus on a random sample of the population, you'd get a much lower number. There aren't currently 1.2 million infected people in Sweden. Positivity rate of tests also doesn't account for previously infected and recovered individuals. Like, Sweden's positivity rate remaining constant as they ramp up testing doesn't mean they have increasing numbers of sick people, it means they weren't previously even testing all the sick people, much like the US in April.

I'm aware of what it is. It's the best metric we have. If you're extrapolating lower numbers from it, you're making assumptions.

The testing meant to show total rate of people who had ever been infected is antibody testing, and the last I saw out of Sweden they were at 7.3%. The number is certainly higher by now, as that was like a month ago, but I don't know if any more recent data is available. Regardless that was after the bulk of the deaths had already occurred, so it's not likely to have increased dramatically since then.

Antibody testing, of course, is subject to even more confounding variables than testing positivity. Not only will the testing pool still be slanted towards those who are or have been sick, but it'll also be a lower sample size, and reflecting a more vague time period.

You're extrapolating a huge amount from extremely limited data, building on various personal assumptions, and using that to support hypotheses very much at odds with the experts in the field (and hypotheses which you already quite strongly believed in, and wanted to be proved true).

 

[tstorm823]

Antibody testing, of course, is subject to even more confounding variables than testing positivity. Not only will the testing pool still be slanted towards those who are or have been sick, but it'll also be a lower sample size, and reflecting a more vague time period.

The idea is that it reflects a broader time period. That's a feature, not a bug. I don't know why you think a lab doing a randomized sample would be slanted towards sick people. And lower sample size is less important than sampling method. A small randomized sample is a more valuable than 100x bigger self-selected sample.

 

[McElroy]

Experiments with the antiviral Remdesivir have turned the drug so popular that the US will hoard it all. Tbf, if it works as advertised (fewer hospital days per patient, and not because they die faster) then they probably need it the most.

Meanwhile in Finland most people have returned to their normal schedule, but roughly a dozen new cases are still being discovered each day. Spirits are high nevertheless.

 

[Silvanus]

The idea is that it reflects a broader time period. That's a feature, not a bug.

It's neither a feature nor a bug: it's unavoidable in antibody testing. But it's certainly unhelpful if you plan to track what stage of an outbreak a country is in, or what the trajectory is, because those antibodies could date from any time.

You could study the growth in antibody rate if you held follow-ups... but the randomised tests didn't.

I don't know why you think a lab doing a randomized sample would be slanted towards sick people.

You realise the randomised antibody tests in Sweden represent a minuscule proportion of antibody tests administered, right? The majority have not been randomised.

In fact, a huge number of them were self-selected, dependent on where you work, the result of referrals, and/or cost the individual money. There's so many confounding variables it's getting hard to keep track.

And lower sample size is less important than sampling method. A small randomized sample is a more valuable than 100x bigger self-selected sample.

Depends on the difference in scale. The size of randomised study that I can find it in the area of 1000 people, without a follow-up, which is statistically insignificant and tells you nothing about trajectory. And that's against infection tests of about 44 per 1000 people, coming to about 440,000.

You're selecting the data to fit a conclusion you've already drawn, not drawing your conclusion from the data.

 

[tstorm823]

It's neither a feature nor a bug: it's unavoidable in antibody testing. But it's certainly unhelpful if you plan to track what stage of an outbreak a country is in, or what the trajectory is, because those antibodies could date from any time.

Correct. It does not tell you about trajectory. It tells you about scale. Tests, death rate, hospitalizations, etc. Those do an alright job with plotting trajectory when done consistently (which they didn't do the tests in Sweden consistently, so deaths and hospitalizations are better proxy variables for trajectory there). You do serology studies to establish scale. When the question is "what percentage of people have been infected and recovered", that isn't a question of trajectory, that is a question of scale.