Thread by @justbbanks

There's still a lot of misunderstanding about HMG response to #COVID_19uk. I'm no epidemiologist, but I *am* an expert at explaining biological ideas to people, so here is an explainer thread of the situation. Corrections / questions welcome. 1/n

First up - vaccines and immunity.

A vaccine is a medicine which helps you become immune to a particular disease without making you ill. Your immune system responds to the weakened version of the disease (the vaccine), thus building immunity to the real disease. 2/n

A vaccine 'trains' your immune system to fight the real disease should you encounter it. Think of it like Neo learning Kung Fu in The Matrix - he developed all the moves without ever facing a real opponent. So when he eventually has to fight, he kicks Agent Smith's arse. 3/n

You can also become immune to a disease by getting it and surviving. This is like getting into a fight and managing to win. Now you know how to win that fight next time round, (as long as the opponent doesn't change their tactics!) The downside is you get your ass kicked... 4/n

There are some complexities to vaccination, though. Firstly, viruses regularly change their structure through random mutations, so a vaccine which works one day may not work a few weeks later. Likewise any immunity gained against a virus can disappear if the virus mutates. 5/n

Now onto herd immunity - the least understood aspect of this.

Herd immunity is typically achieved by vaccinating as many people in the community as possible. These people become immune to the target disease, so they can't spread it. 6/n

But there are still people who haven't been vaccinated, so are vulnerable to the disease. How does herd immunity help them? Think of it like creating lots of firebreaks in a forest, where a fire can't spread across. The more people vaccinated, the more firebreaks there are. 7/n

It's a probability thing. As you vaccinate more people, the chances of a non-vaccinated infected person infecting another non-vaccinated person drops considerably. Since the infection can't spread easily to new people it burns out. 8/n

Some important notes about herd immunity:

1. It's usually developed in advance as it's a strategy to avoid outbreaks happening in the first place.
2. If a virus mutates then herd immunity can fail as people aren't immune to the new organism. (Why we get 'flu every year.) 9/n

So how does this relate to the HMG response to this pandemic? The original plan announced last week seems to be:
- Continue as before so the virus spreads through the population.
- The hope is that developing COVID-19, then recovering from the disease, confers immunity. 10/n

- Self-isolation, increased cleaning regimes, and asking elderly and vulnerable people to get off-side for a bit should slow down this spread, and take some of the heat off the NHS.
- Then, a few months down the line, most people should have developed immunity. 11/n

- Keeping the schools open seems to be so the virus shoots through younger people more quickly. Since young healthy people seem pretty resilient to COVID-19 mortality rate among <19s should be low, adding thousands to the "resistant" herd every day. 12/n

- Once most of us have been exposed to (and survived) the virus, the chances of it continuing to spread to older / vulnerable people should drop because we've built herd immunity.

Normal society can come back to life.

13/n

At least that's the theory, but it's a different approach to most of the world and at odds with WHO advice. The UK is heading into uncharted territory, and it's doing it alone.

So what are the issues with the HMG plan?

14/n

The plan needs the virus to spread, but not so quickly as to swamp the NHS. This is like a controlled burn to manage heathland. If HMG's control measures to slow the spread fail, then the disease burns of control and many will die from lack of available healthcare. 15/n

There are serious questions about whether getting the disease confers immunity. Some people have been sick, recovered, then got sick again. Herd immunity doesn't work if the immune members of the herd get sick again.

16/n

A circulating virus will mutate. Often they mutate to be less lethal so they embed into the human ecosystem, but equally they can become more dangerous. In any case mutating viruses change so much that any immunity can become useless in a relatively short time. 17/n

Although healthy younger people generally survive this virus with few ill-effects, there'll be fatalities. Maybe 6000-odd school kids, plus loads more adults, simply because we're not locking down. So herd immunity will have a high cost. Are we ready for that? 18/n

Further to keeping the schools open, while the kids are generally likely to be okay, exposing pupils to this virus exposes their wider community to it as well. Many virus infection rates fall during holidays as schools are hotbeds of disease transmission. 19/n

While HMG backtracked on its guidance about large gatherings, the suggestion that infections spread as easily in a pub as they do in a stadium shows a worrying lack of understanding. It's not the venue which matters... 20/n

... it's the number of people touching the same handles, ATM keypads, toilet doors in that venue which matters, which is far fewer in a pub than in a stadium. One recent study in China showed that many people can become infected in this way from one infected individual. 21/n

To conclude / TLDR. HMG's plan is a unique response to the crisis, different to the rest of the world. While there is some logic behind it, it's untested and there are many questions about whether it will work. What is certain is that it will cost lives. 22/n

When this is over - and it will be over soon enough - those who died will be counted, and judgement will be passed. Then we will see if HMG's gang of misfits and weirdos are maverick epidemiological heroes, or arrogant, dangerous, fools. ENDS