Herd immunity

[Immaculatemisconception]

Covid: UK ‘very close to herd immunity’ as antibodies estimated in 90% of adults!

Public Health England expert says country ‘very close’ to reaching critical level of protection!

Great news.

@MarshaBradyo

If you still transmit with vaccine then do you get closer to immunity with natural infection?

Before it wanes that is, if it does

Feels confusing

According to studies, vaccine confers more immunity than infection.

@MarshaBradyo

If you still transmit with vaccine then do you get closer to immunity with natural infection?

Before it wanes that is, if it does

Feels confusing

You could just hit the magic 84% with natural infection but absolutely everyone would need to catch it at the same time with no further mutations leading to increased transmissibility or immune escape - with that number of infections one or both would be pretty much guaranteed.

"According to studies, vaccine confers more immunity than infection." - not true for delta. Recent data out of Israel suggests Pfizer has only 64% efficacy against delta whereas the latest estimate I could find is about 84% for natural infection.

Ok yeh that makes sense

How exactly have they worked this out?

This is positive news, although antibodies are only part of the immune response. So it's not a complete picture.

No vaccine protects 100% of the people who get it 100% of the time. The concept of 'vaccine effectiveness' isn't new; the flu vaccine mix is usually only about 40-60% effective in any given year. Which is why some people who have been vaccinated against flu still get flu. (The same goes for other diseases, such as meningitis, diphtheria, mumps and so on. Although most other vaccines are much more in the 85-95% effectiveness range.)

I also think many people misunderstand what herd immunity actually means. It isn't some Avengers-style forcefield that stops anyone getting ill ever.

It's imperfect, like every other strategy, but the aim of herd immunity is to help prevent major, galloping community outbreaks like we've seen with covid over the last year and a half.

Herd immunity as a concept rests on three things working together at a societal level: vaccinations, immunity through exposure/recovery, and a certain level of natural pre-existing immunity to that particular disease. (This last aspect is usually a small minority, but it does happen; one of my brothers discovered a few years ago that he's naturally immune to HIV, for example.)

It's actually a good example of social responsibility happening semi-organically. There will always be people who aren't immune to any given disease, whether through natural vulnerability or lack of vaccination (or both). But if there's a sufficient level of herd immunity among the population as a whole, those who are vulnerable are at least part protected or buffered by the members of the population who are immune.

It's another way to protect the vulnerable. It isn't 100%, but then what is?

inews.co.uk/news/health/herd-immunity-will-never-be-reached-in-the-uk-but-covid-19-vaccine-protection-is-enough-1089971

The UK will never reach herd immunity from Covid-19 – but it will not need to due to the protection from severe disease coronavirus vaccines give us, a leading scientist has said.

Paul Hunter, professor in medicine at the University of East Anglia, said given the reproductive number – or R number – of the dominant Delta variant is 8, herd immunity would only be reached when around seven-eighths of the population (88 per cent) are protected. And given the Oxford/AstraZeneca and Pfizer vaccines are slightly less effective against the delta variant the target is out of reach.

He toldi: “The effectiveness of the AstraZeneca vaccine against clinical infection with delta is about 88 per cent and likely effectiveness against asymptomatic infection somewhat less. We do not know the value for all infection for the delta variant but it was 67 per cent for infections in the phase 3 trial pre-delta, so assume 70 per cent.
Therefore to achieve herd immunity 88 per cent would need to be immune – with a vaccine that is only 70 per cent effective you would need to immunise 125 per cent of the UK population. But that is an underestimate because it does look like vaccine and natural immunity wains with time.

“That is why we will never reach herd immunity but we do not need to, as vaccine substantially reduces the danger of getting severe disease on first infection. That is enough. Covid is here to stay but not as we know it, more like the other coronaviruses which are a cause of the common cold.”