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Vital coronavirus questions answered: What is herd immunity? How can you help yourself?

By Ben Spencer for the Daily Mail
March 13, 2020 | Updated: March 14, 2020

What is the Government's plan?

Officials want to delay the peak of the outbreak. They can no longer contain the virus – it has arrived and is spreading through the population. In a worst- case scenario, 80 per cent of people will become infected.

By telling people to self-isolate for even the mildest symptoms, they hope to 'flatten the curve' of the crisis – or, as Boris Johnson put it, 'squash the sombrero'.

This means delaying onward transmission and spreading out the number of patients who would overwhelm the NHS if they all contracted the virus at once. They also hope that by delaying the peak to the summer months, they will spare hospitals from simultaneously dealing with coronavirus and winter diseases such as flu and norovirus. There is also a hope that, as the virus passes through the country, we will develop 'herd immunity'

What does herd immunity mean?

This is when enough people become resistant to a disease that it can no longer spread among the rest of the population. Because Covid-19 is a new disease, none of us has immunity. But if enough people get the virus – and so become resistant to a second bout – the virus will struggle to find anyone to spread to, and the numbers will start to decline.

What does this strategy mean for me?

For most people, officially at least, it is a case of carry on as usual and wash your hands more often. The major directive is that anyone who has symptoms, however mild, should go home for a week. This applies to anyone who develops a persistent cough or has a temperature higher than 37.8C.

How many have to get the virus to achieve herd immunity?

Experts believe about 60 per cent of the population (40 million people) need to be immune. That is because the outbreak will start to decline only when most infected people stop passing it on. If each person passes the virus on to one more person, the size of the outbreak will stay the same size. At the moment each person passes it on to about three others, on average, so the outbreak grows quickly. When the rate of onward transmissions falls from three to fewer than one, the outbreak will start to decline. So for the outbreak to tail off, two out of every three people who get the virus need to become immune.

Why is the 60% figure lower than for other diseases?

Herd immunity against measles, for example, requires at least 95 per cent of people to be immune to the disease – usually through vaccination. That is because measles is far more contagious – each patient passes the viral infection on to 20 others. If an outbreak is to die out quickly at least 19 of those have to already be immune – so 95 per cent of the original 20.

Do all scientists think herd immunity will protect us?

They hope it will work. But critics say several unresolved features of the Covid-19 infection may thwart the strategy. First, we don't yet know how much immunity is triggered in the body of someone who becomes infected. There are have been reports in China, for example, that some people have become infected twice. Second, it is not clear how long immunity lasts. The flu jab, for example, has to be given each year because immunity against influenza quickly wanes, and the virus mutates each year. But immunity against other diseases – such as TB – lasts at least a decade.

Would a vaccine help?

Yes. Natural herd immunity is not guaranteed and requires a lot of people to suffer unpleasant illness. And many people will die as a result. A vaccine would accelerate the process, providing immunity without the illness. It would also mean if immunity wanes, an annual jab could be used to top it up. But it is unlikely a vaccine would be ready before the current pandemic ends. It would be invaluable, however, to stop a second wave of the virus hitting next year.

How does herd immunity help the elderly?

The elderly are much more vulnerable to coronavirus, so the Government is hoping to exclude them from the wider strategy of 'carry on as usual'. This means 'cocooning' the vulnerable and elderly with a 'ring' of immune people around them. This relies on the theory that those who are most able to withstand the virus – the young and fit who will mostly suffer mild symptoms – will become infected, then become immune, without passing it on to the old and sick.

How are older people being protected?

Care homes have been told to take action – including stopping visits from anyone with a cough or fever. Care home residents will be isolated in their rooms and staff will wear protective equipment when they care for them. In hospital, decisions may be taken not to treat the most frail people if intensive care units become overwhelmed with patients.

And those who live in their own homes?

Officials have also given notice that in the coming days they may ask all elderly people to stay indoors to protect themselves. But this has not been implemented yet for fear of isolating them for months – a situation that would lead to loneliness and depression.

Why isn't the UK taking much more stringent action?

The Government's scientific advisers insist it is a matter of timing. In the next few weeks, as case numbers climb, they may introduce further measures – including telling entire families to self-isolate and closing schools. But they insist the time to do this has not yet arrived.

Why not act now?

They believe the crisis is going to last for several months. Delaying the introduction of a 'lockdown' will minimise the impact on society and the economy. It will reduce 'crisis fatigue' and make it more likely that people will follow health advice just when the outbreak is peaking.

Aren't some firms taking things into their own hands?

Yes. Employers, businesses and many other organisations are taking action over and above the Government's advice. Concerts, sporting events and conferences have been called off, airlines are cancelling flights, courts are in lockdown and many companies have told their staff to work from home.

Why not close schools, like other countries?

Boris Johnson says this would do more harm than good – and have a major impact on the NHS as crucial staff members take time off to look after their children. His advisers say to be truly effective you would have to shut a school for three months or more – and even then it would be almost impossible to stop children from playing with each other, undermining the impact. Elderly people would also suffer extra exposure because they are likely to look after grandchildren sent home from school.

What about mass gatherings?

Ministers are expected to ban mass gatherings as early as next weekend – and are drafting emergency legislation next week to allow them to do so. They have been cautious about taking this step because they worried it would place a major burden on society and the economy. In reality, however, the decision has been taken out of the Government's hands. The Premier League has suspended all games until April, the London Marathon has been called off, concerts have been postponed by organisers and charities and academic groups are cancelling annual conferences.

What exactly does self-isolating involve?

Anyone who has to self-isolate because they have a cough or a raised temperature has to spend a week at home without leaving. They should stay two metres (three paces) away from other people in the home, sleep alone, and ask for food and supplies to be left outside the door.

Do I need a test first?

No. The Government has decided to stop testing people unless they are in hospital. Now anyone who has symptoms, however mild, must self-isolate.

Should I contact the NHS?

No. It has been left to people to act responsibly once they have symptoms. The NHS is trying to stop its staff and patients becoming infected – and needs to save resources for the seriously ill.

What if my symptoms get worse?

Use NHS 111 online or call NHS 111. If you get seriously ill, dial 999.

When can I go back to work?

After seven days, if you feel better and no longer have a fever, you can return to your normal routine. If symptoms last longer than seven days, check NHS 111 online.

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