Herd immunity is a result of enough people in a population having developed an immunity to a virus, whether by vaccine or by having had it before and recovered, for the disease to stop spreading.

This is according to Professor Martin Hibberd of Emerging Infectious Disease at the London School of Hygiene and Tropical Medicine.

This is the thinking behind vaccinations and why they are so vital. The number of infections is reduced because a certain threshold of people is already immune to the disease without actually having to be ill in the first place. This way, the body does not have to fight off the disease itself.

Over time, the chances of others being infected will be reduced.

Eventually so few people will be susceptible to the disease that it will have no one to spread to and it will disappear.

The point is to bring that threshold down so that a minimal number of people get infected, as some of them may die if they contract the disease.

Social distancing can have a similar effect to vaccination. It reduces the number of people that one person infects, therefore lowering the point at which herd immunity comes into effect and the disease stops spreading.

The problem is that until that threshold is met, those who are vulnerable can catch the disease and die.

The United Kingdom, until recently, was hoping to rely on herd immunity as a strategy to deal with the Covid-19 pandemic. There is no vaccine for Covid-19 so it was planning for people to get sick and recover.

This is why at first the UK did little to contain the spread of the disease. It chose to introduce restrictions gradually as opposed to trying to flush the virus out as quickly as possible.

The UK government’s chief scientific adviser Sir Patrick Vallance has said that 60% of the population would need to get ill with Covid-19, recover and become immune in order to build up this herd immunity.

This strategy is in direct conflict with the World Health Organisation’s recommendations.

“The idea that countries should shift from containment to mitigation is wrong and dangerous,” said the WHO’s Director-General Dr Tedros Adhanom Ghebreyesus in an address on 12 March 2020.

He continues to insist that this is a controllable pandemic if containment is central to all strategies around the world.

WHO has called on all countries to prepare and be ready for the arrival of the virus in parts of the country where it has not yet spread to.

Each must prioritise detecting, preventing and treating the virus. “You can’t fight a virus if you don’t know where it is,” said Ghebreyesus. To break the chain of transmission, each infection must be found, isolated, tested and treated.

Transmission of the virus must be reduced and suppressed. This includes slowing down transmission.

The WHO has spoken out directly against the herd immunity strategy of the UK. “We don’t know enough about the science of this virus, it hasn’t been in our population for long enough for us to know what it does in immunological terms,” the WHO’s spokeswoman Margaret Harris told BBC Radio 4 on 14 March.

Researchers from the Imperial College found that the UK’s strategy would lead to 260,000 deaths. This includes deaths from the virus and those from other illnesses which could not be treated because the healthcare system was overwhelmed.

The UK government then quickly changed its tune over the past week and now schools, gyms, cinemas, pubs and restaurants have been closed. It is now also encouraging people to avoid unnecessary social interaction and to adhere to the principle of social distancing.

Those who display Covid-19 symptoms must stay at home for a week and those they live with must stay at home for two weeks.

Yet, the UK healthcare system might be overwhelmed by Covid-19, like the Italian health system, in two weeks’ time, said Prime Minister Boris Johnson on 22 March. MC