The UK Government says two-thirds of the British population will need to be infected with Covid-19 to help prevent the disease from spreading in the future.
Medically reviewed by Dr Roger Henderson and words by Jessica Rapana
While many European countries are cracking down on the spread of coronavirus by introducing restrictive measures, such as closing schools and banning mass gatherings, the UK government has announced a more nuanced ‘herd immunity’ approach.
Following a COBRA meeting on the virus last week, the government’s chief scientific advisor Sir Patrick Vallance said that about 40 million people in the UK may need to catch Covid-19 to build up herd immunity in order to manage the spread of the infection and prevent the disease from coming back in the future.
However, the herd immunity strategy has been criticised over its potential human cost, with experts warning it could put the NHS under additional stress. In an open letter to the UK Government more than 200 scientists have warned that the current approach could ‘risk more lives than necessary’ and have urged the government to introduce tougher measures to tackle the spread of Covid-19.
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But what exactly is herd immunity and how does it work? A number of experts commenting on developments via the Science Media Centre have expressed their concern. Professor Willem van Schaik, professor of microbiology and infection at the University of Birmingham, has described herd immunity and how it could affect the coronavirus pandemic:
What is herd immunity?
In theory, herd immunity means not everyone in a community needs to be immune to prevent the spread of a disease. ‘Herd immunity describes the phenomenon that at-risk individuals are protected from infection because they are surrounded by immune individuals. The spread of the virus is thus minimised,’ Prof van Schaik says.
How does herd immunity work?
Herd immunity describes the resistance to the spread of a contagious disease within a population due to a sufficiently high proportion of individuals being immune either through vaccination or by developing immunity after infection.
‘Currently, we talk mostly about herd immunity in the context of vaccines. If a sufficiently high number of individuals in a population are vaccinated, they will provide herd immunity to the small number of people that are not vaccinated,’ says Prof van Schaik.
What percentage is needed for herd immunity?
Prof van Schaik has expressed his concerns about the success of using herd immunity to curb the rate of infection. ‘Unfortunately, a very rough estimate suggests that we will only reach herd immunity to Covid-19 when approximately 60 per cent of the population is immune (and remember that immunity is currently only reached by getting the infection as we have no vaccine),’ Prof van Schaik says.
What are the risks of herd immunity?
The professor expressed serious concerns about the risk implications involved. ‘The major downside is that this will mean that in the UK alone at least 36 million people will need to be infected and recover. It is almost impossible to predict what that will mean in terms of human costs but we are conservatively looking at tens of thousands of deaths, and possibly at hundreds of thousands of deaths.’
‘The only way to make this work would be to spread out these millions of cases over a relatively long period of time so that the NHS does not get overwhelmed.’
He adds, ‘I note that the UK is the only country in Europe that is following this strategy. Other countries also use scientific advice to guide their research and it is unclear to me why the UK is alone in their laissez-faire attitude to the virus.’
Herd immunity examples
Herd immunity currently exists for the flu, thanks to large proportions of the population getting the flu vaccine that can protect non-immunised individuals. However, given there are different strains of the flu, it is not always 100 per cent effective.
Covid-19 is unique in that it is a novel virus, meaning that everyone is currently at risk of infection. ‘Herd immunity can only be reached by widespread vaccination (but there is currently no vaccine, and it may take a long time before an effective vaccine becomes available) or by individuals falling ill or recovering thereby developing natural immunity against the virus,’ Prof van Schaik says.
How effective is herd immunity?
While it is true that herd immunity makes it harder for a disease to spread due to people becoming immune after already catching it or getting vaccinated, there are ‘considerable risks and downsides’ of letting a potential lethal infectious disease burn through a population in order to reach herd immunity.
‘This is why we still need to all work together to try to slow down and minimise the spread of Covid-19 by practicing hand hygiene and social distancing. This will hopefully reduce the pressure on the NHS, allowing for more people to be treated and thus reducing the number of people dying of this infection,’ advises Prof van Schaik.