Coronavirus: could 'herd immunity' be effective and what is it?

A woman is pictured at the Rajiv Chowk metro station in New Delhi wearing a mask on 13 March. India has had 81 confirmed cases. (Getty Images)

The UK's chief scientific adviser is optimistic the government’s approach to tackling the coronavirus outbreak will create “herd immunity”.

Sir Patrick Vallance told ITV News if 60% of Britons catch the circulating Covid-19 strain we may all be “a bit protected”.

The government has faced criticism for not doing enough to combat what is now being referred to as a pandemic.

Unlike Ireland and other parts of Europe, the UK is yet to close schools and put a blanket ban on large gatherings.

Sir Patrick argued Covid-19 is expected to be an issue for “months”. The UK government is therefore not looking to suppress the outbreak, but create herd immunity.

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“When you look at infections across whole communities, when you get up to about 60% who've had it, you get something like herd immunity, which means we're then all a bit protected from it,” he told ITV News.

“So if it does get to that level, that provides quite a lot of protection going forward”.

Speaking on BBC Radio 4’s Today programme, Sir Patrick added: “What we don’t want is everybody to end up getting it in a short period of time so we swamp and overwhelm NHS services.

“Because the vast majority of people get a mild illness, [we want] 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”.

The coronavirus, colds and flu all cause fever, but only the coronavirus triggers shortness of breath. (Yahoo UK)

Covid-19 is thought to have emerged at a seafood and live animal market in the Chinese city Wuhan at the end of last year.

It has since spread globally, with cases being confirmed in more than 100 countries across every inhabited continent.

Since the outbreak began, over 137,000 people have tested positive for the virus worldwide, according to John Hopkins University data.

Of these patients, more than 69,000 have “recovered”.

China is still the epicentre of the outbreak, recording more than 80,900 cases since Covid-19 was identified.

Some are optimistic the situation has “curbed”, however, with the number of incidences reported in China plateauing since the end of February.

Just eight new cases were noted across the whole country on Thursday.

Outbreaks have taken hold elsewhere, however, with Italy alone having more than 15,000 confirmed patients and over 1,000 deaths.

The UK has carried out more than 29,000 tests, of which 798 have come back positive and 10 patients have died.

What is herd immunity?

Herd immunity comes about when a sufficient number of patients are immune to an infection that it cannot “take hold” in the community.

This is one of the main reasons supporting vaccinations.

While healthy individuals will unlikely become seriously unwell if they develop an infection like flu, the elderly or otherwise ill could develop complications.

Certain people – like those having chemotherapy or HIV patients – may also be unable to have vaccinations due to their suppressed immune system.

They therefore rely on other individuals to have the jab in order to create herd immunity and keep them safe.

Covid-19 is one of seven strains of the coronavirus class that are known to infect humans, with none having a vaccine.

Virtually unheard of at the start of the year, Covid-19 is somewhat mysterious.

When it comes to measles, 95% of people need to be vaccinated for everyone to be protected.

Covid-19’s “herd immunity percentage” will depend on its basic reproduction number.

This is the number of people a patient statistically goes onto infect.

For example, a number of three means that every Covid-19 patient is expected to pass the virus onto three others.

“If it is bigger than one, the epidemic grows, and if less than one, it shrinks,” said Dr Thomas House from the University of Manchester. 

“Suppose the basic reproduction number is three, so the epidemic initially grows, but that at a later time over two-thirds of people have become immune. 

“Then the average case will make three infectious contacts, but we expect two of these will not lead to new cases due to immunity and so the epidemic will no longer grow. 

“Ideally it happens through vaccination, which does not involve illness. 

“It can also happen due to infection leading to disease and later recovery.”

With Covid-19 having no “set” treatment, prevention is all the more important.

Health officials are urging the public to wash their hands regularly and maintain social distancing.

“Social distancing measures do not lead to herd immunity, so when they are lifted the epidemic may grow again,” said Dr House. 

“Whether we aim for it or not, herd immunity will happen at some point in the future since neither a growing epidemic nor social distancing measures can continue forever, and the aim of policy should be for this to happen with the minimum human cost possible.”

A man is pictured wearing a protective suit while disinfecting a tram in Zagreb on 13 March. Croatia has had 31 confirmed cases. (Getty Images)

Covid-19’s basic reproduction number has been debated.

Mid-February, scientists from the London School of Hygiene & Tropical Medicine estimated Covid-19’s reproduction number fluctuated between 1.5 and 4.5 before travel restrictions were introduced in Wuhan, stressing “substantial uncertainty”.

This led them to predict the outbreak may peak in “mid-to-late February”.

Speaking at the time, Dr Robin Thompson from the University of Oxford, said: “One proviso must be forecasting the peak of any outbreak is challenging, and so there is significant uncertainty in estimates of both the timing of the peak and the total number of cases that will occur.” 

Professor David Heymann, also from the London School of Hygiene & Tropical Medicine, previously told Yahoo UK basic reproduction numbers “change daily as new information comes in”.

Sir Patrick went onto say herd immunity could become particularly useful if Covid-19 becomes a seasonal infection, like flu.

Although unclear, Yahoo UK previously reported how the virus may ease as it gets warmer only to re-emerge in the northern hemisphere’s winter.

In order to achieve widespread immunity, more deaths will occur.

The WHO has estimated Covid-19’s global death rate to be 3.4%, which many experts called a likely “overestimate”, adding 1% seems more “reasonable”.

The vast majority of deaths are affecting the elderly or otherwise ill, with these people having to be protected.

Young healthy people tend to make a full recovery, however, Jermey Rossman – from the University of Kent – told The Conversation a proportion of these individuals will statistically die if we let the virus “pass through the community”.

“We can and we must do better than that,” he said.

“China is rapidly controlling the spread of Covid-19 without requiring herd immunity.”

Officials in China have implemented strict quarantine measures, with Wuhan on “lockdown” since the start of the year.

Professor Martin Hibberd from the London School of Hygiene & Tropical Medicine added: “When about 70% of the population have been infected and recovered, the chances of outbreaks of the disease become much less.

“In a good scenario, the 70% infected, recovered and immune would be people who were expected to have mild disease and the 30% who were vulnerable to severe disease would be protected by this herd immunity.

“The government plan assumes herd immunity will eventually happen and from my reading hopes this occurs before the winter season when the disease might be expected to become more prevalent.

“However, I do worry that making plans that assume such a large proportion of the population will become infected (and hopefully recovered and immune) may not be the very best we can do. 

“Another strategy might be to try to contain [the outbreak] longer and perhaps long enough for a therapy to emerge that might allow some kind of treatment”.

Visitors of the Golden Temple in Amritsar, India, are pictured wearing masks on 13 March. (Getty Images)

What is the new coronavirus Covid-19?

Most of those who initially caught Covid-19 worked at, or visited, the “wet market” in Wuhan.

The virus mainly spreads via infected droplets that have been coughed or sneezed out by a patient.

There is also evidence it may be transmitted in faeces and urine.

Early data suggests four out of five cases are mild, with a patient’s immune system naturally fighting off the virus.

In severe cases, pneumonia can come about when the infection causes the alveoli (air sacs) in the lungs to become inflamed and filled with fluid or pus.

