Herd immunity not possible without a vaccine.

[bibbitybobbitycats]

I have been doing a bit of reading about herd immunity, as I wasn't sure I understood the concept properly.

One thing that I didn't realise is that control of an infectious disease without a vaccine has never been achieved before (according to this article):

theconversation.com/can-we-actually-learn-to-live-with-coronavirus-not-until-we-have-a-vaccine-147792

I did wonder if this was completely true, as if so, how did the plague die out? This is informative:

www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31924-3/fulltext

Which says that herd immunity to plague, malaria, and typhus occurred because people "no longer lived in close association with the requisite vectors" (for example fleas, dirty water). It also says that without a vaccine, many people would have to die from COVID-19 before population immunity is achieved.

It would seem that to achieve herd immunity without a vaccine we would need around 47 million people to be infected with the virus. Obviously, this would lead to tens of thousands, maybe hundreds of thousands of deaths and would leave many people with health problems.

So why do some people think trying to achieve herd immunity without a vaccine is a viable, ethical policy? What am I missing?

@raddledoldmisanthropist

What I don't understand is why some people think HI is a viable policy for this disease in the absence of a vaccine.

I think most of them fundamentally don't understand how high the death rate will be if we can't get people in ICU quickly when they start struggling to breathe.

I also think they don't get that the economy will shut down far worse than it has once the disease is wildly uncontrolled.

A lot of them are just conspiracy nutters anyway or people losing jobs who are desperate for a magic solution.

Yes, this is pretty much my thinking.

For herd immunity you need enough people who are are immune and resistant such that the disease does not transmit
A problem with covid is that people who are asymptomatic can still transmit the disease, it is very difficult to stop the transmission when you cannot identify the people who are doing the transmitting most of them are hidden because of not having symptoms or any signs of illness

The biggest reason Covid is so bad is because it's new and we have little or no pre-existing immunity
But we do have pre-existing resistance, many people exposed to the virus do not develop symptoms and are not harmed by it

I think people think that it is like ripping off a plaster, if we're all likely to get it, might as well get it over with. They don't consider that although the death rate might only be 1%, the hospitalisation rate is 10% and if we can't hospitalise those other 9% bacause so many people are sick at the same time, they will die without treatment. (Percentages are entirely made up to illustrate the point.)

But we do have pre-existing resistance

There is some evidence we have some. It's an open question how much but clearly not enough to stop the spread. There are 4 human Coronaviruses which may have some effect but they are not closely related to Covid because it's cross-species.

many people exposed to the virus do not develop symptoms and are not harmed by it

I think there is still some debate about how asymptomatic people really are (e.g. feeling a bit weary or having a slight sniffle is ignored).

The people who are most likely to be asymptomatic are the very young. This is the total opposite to most similar illnesses and suggests that things like viral load and phagocyte response might be more important than any form of partial immunity.

Regardless a flu which puts me in bed for weeks and you shrug it off doesn't mean you were immune.

Covid also seems to cause a much wider range of both symptoms and severity than similar diseases.

One thing that I didn't realise is that control of an infectious disease without a vaccine has never been achieved before (according to this article):

Manaus in Brazil has reached herd immunity. This is not a good thing because it means 60+% of people were infected.

Covid also seems to cause a much wider range of both symptoms and severity than similar diseases
it does seem bizarre that a virus which has only just jumped the species barrier has come pre equipped with an enhanced ability to invade and infect such a wide range of human tissues

This is what we are trying to do with Covid- vaccinate the vulnerable while the rest of the population gets it so that, over several years, it becomes part of the normal reservoir of flus

That isn't exactly right I don't think@raddledoldmisanthropist Someone has linked the john snow memo up thread and it is worth reading this carefully as it succinctly covers distinguishing factors between COVID - ie our current state of knowledge of COVID - and other diseases. @bibbitybobbitycats it is worth you reading it to as it answers your first post pretty well. The memo was a riposte to a paper which proposed and supported HI as a strategy.

A key point is that there is no evidence for lasting protective immunity to SARS-CoV-2 following natural infection according to current knowledge. Immunity is one of the tricky aspects of this disease.

As I understand it, the first generation vaccines are a matter of months away, they are going through final approvals now. All bar one I think do not provide sterilising immunity ie would not stop you getting covid or transmission but would protect you from dying/being hospitalised for serious complications arising from the infection. So my understanding is that the 1st gen vaccines could be effective to reduce the status of the disease to something more manageable, like other coronaviruses. R&D will continue obviously. If you want authority for that, if you search my username I have linked a recent webinar with Gabriel Leung.

Another issue with herd immunity is that, I believe, young people/people who get it mildly can still suffer long term damage to vein and vital organs. So it is the distinguishing features of this disease which are so difficult and the more people understand the more they will cooperate.

The first generation vaccines are hoped (by scientists) to bring some level of normality back - but it will take time and there will be political arguments no doubt about who pays for the vaccines. Still, if people understand what is going on well, it will help with cooperation and hope.

@Sarahsah4r4 there have been other diseases caused by bats which have attacked the organs and brain - if you google you will find examples - there are distinguishing factors for example they might have been caused directly to a human by a bat by a scratch but not have spread person to person.

it does seem bizarre that a virus which has only just jumped the species barrier has come pre equipped with an enhanced ability to invade and infect such a wide range of human tissues

I think people underestimate how much 'flu' can vary between individuals but, yes, Covid does seem to have a particularly varied response.

I have no clue how typical/atypical that is for species jumpers although it has long been a trope of epidemiology that sooner or later a virus would come along again which rolled double 6s and it would be particularly deadly because of globalisation.

@notevenat20

One thing that I didn't realise is that control of an infectious disease without a vaccine has never been achieved before (according to this article):

Manaus in Brazil has reached herd immunity. This is not a good thing because it means 60+% of people were infected.

That article says herd immunity there not yet proven and cases may be on the rise again?

@johnsnowmemo thanks for that post, I will do some further reading.

A key point is that there is no evidence for lasting protective immunity to SARS-CoV-2 following natural infection according to current knowledge. Immunity is one of the tricky aspects of this disease.

I know. I was indeed speaking somewhat simplisticly but I did make clear that it's pretty certain immunity won't be lasting and I mentioned that the timescale for things to return completely to normal would be years. I take your point that the 'protect the vulnerable' may not mean they don't get it.

How long and how effective is very much an open question at the mo. Even if vaccination is needed every year and annual flu deaths are permenantly increased due to covid, that's still a much better situation than we have now.

“If it were true (it's not), then a vaccine would also only last 60-90 days.”

That’s not true either. Immune responses induced by vaccines are dependent on the viral vector used and the adjuvant used. For example the Oxford vaccine is an adenovirus so immune responses generated such be more like those generated in response to adenovirus infections than those generated to SARS cov 2

Some viruses disappear without herd immunity. They tend to be those that are not contagious before symptoms and rapidly progress to hospitalisation/ death so get little chance to spread. For example, SARS and mers. Ebola is another example but that remains in the animal reservoir so reappears from time to time.

[quote johnsnowmemo]@Sarahsah4r4 there have been other diseases caused by bats which have attacked the organs and brain - if you google you will find examples - there are distinguishing factors for example they might have been caused directly to a human by a bat by a scratch but not have spread person to person.[/quote]
Completely off topic but I wonder if the myths around vampire bats are based on a prior (before recorded history) covid virus being spread from bats to humans and causing issues with blood. People are a woo about bats and I wonder if its based on an historical event rather than just stories.

HI can't be achieved if immunity isn't long lasting anyway. I don't think we know if having a second infection results in a milder or more severe case.
If each subsequent infection is worse then people will be more vulnerable each time.
Fingers crossed for a vaccine!

Re bats - they need a uniquely high metabolic rate to be able to fly and this allows them to cope with lots of diseases that would kill other mammals. This means that they carry many more pathogens than other mammals and thus the human revulsion for them is useful to us.

This means that they carry many more pathogens than other mammals and thus the human revulsion for them is useful to us.

Which is a shame because they are delicious.

I am not certain, but I don't think it is true that if immunity after natural infection with wild virus only lasts, for example, six months, then immunity from a vaccine would be of equally short duration. Sometimes vaccines can be created to provoke a more lasting immune response than natural infection. Booster vaccines would likely still be needed in time though.

I heard the Oxford Professor who participated in the Great Barrington Declaration (Sunetra Gupta, I think) say that it was a fundamental misconception that immunity has to last longer to achieve HI.

Unfortunately, the Radio 4 interviewer cut her off at that point, which really frustrated me because I wanted to know what she meant. I've tried researching since, but didn't find anything. I'm desperate to understand how this could be.

Yes, this is why smallpox swilled around for thousands of years even when lots of people had had it.

Ooh, I just found an interview with the other tow Great Barrington professors and her described it as this:

While Covid-19 reinfection can occur, it is so rare that it does not affect herd immunity.
'Even if immunity wanes over time, which is plausible, that will not happen completely nor simultaneously for everyone, so there will always be enough immunity around to avoid a repeat of this spring.'

Sorry to answer my own question, but I was pleased to finally find an explanation to what Gupta meant.

• Two and he 😳