By Tony Winterburn •
Published: 13 Mar 2020 • 11:14
Sir Patrick Vallance said that he thought the coronavirus was likely to become an “annual virus” and that the strategy was to limit the impact on the NHS but not stop the virus completely.
Asked if there is a fear that clamping down too hard on its spread could see it return, Sir Patrick said: ‘That is exactly the risk you would expect from previous epidemics. If you suppress something very, very hard, when you release those measures it bounces back and it bounces back at the wrong time.
‘Because the vast majority of people get a mild illness, to build up some kind of herd immunity so more people are immune to this disease and we reduce the transmission, at the same time we protect those who are most vulnerable to it. Those are the key things we need to do.’
Using herd immunity to tackle an illness that Boris Johnson admits will claim many lives is controversial, because it is usually reserved for vaccination programmes were no one will die.
In the case of coronavirus, the theory is that if a high enough proportion of the population beats the virus and gains immunity – if it returns next winter it is less likely to find a susceptible person to infect and struggle to spread or die off completely.
Herd immunity is a situation in which a population of people is protected from a disease because so many of them are unaffected by it that it cannot spread.
To cause an outbreak a disease-causing bacteria or virus must have a continuous supply of potential victims who are not immune to it.
Immunity is when your body knows exactly how to fight off a certain type of infection because it has encountered it before, either by having the illness in the past or through a vaccine.
When a virus or bacteria enters the body the immune system creates substances called antibodies, which are designed to destroy one specific type of bug.
When these have been created once, some of them remain in the body and the body also remembers how to make them again. This provides long-term protection, or immunity, against an illness.
If nobody is immune to an illness – as was the case at the beginning of the coronavirus outbreak – it can spread like wildfire.
However, if, for example, half of people have developed immunity – from a past infection or a vaccine – there are only half as many people the illness can spread to.
As more and more people become immune the bug finds it harder and harder to spread until its pool of victims becomes so small it can no longer spread at all.
The threshold for herd immunity is different for various illnesses, depending on how contagious they are – for measles, around 95 per cent of people must be vaccinated to it spreading.
For polio, which is less contagious, the threshold is about 80-85 per cent, according to the Oxford Vaccine Group.
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