‘Herd immunity’ is a phrase you may have heard a lot in relation to the UK’s approach to COVID-19. Here experts explain what herd immunity is and the viability of the UK’s approach to this crisis.
As concerns regarding COVID-19–the novel strain of coronavirus never experienced in humans before–grow every social media platform features individuals giving their opinion and potentially spreading false news about the virus.
Currently, the UK government’s approach to the spread of COVID-19 is to allow the virus to spread through the population in an attempt to engineer a herd immunity. Vulnerable individuals such as those with immunosuppressant disorders have been advised to self-isolate for six months.
The move has been met with widespread condemnation by experts in the control of disease and is in contrast to the procedures underway in other major European countries.
What follows below are important questions about COVID-19 and the UK’s approach to this crisis answered by experts and epidemiologists and ONLY by experts and epidemiologists.
What are the considerations about the development of herd immunity?
“Herd immunity is the term generally used to refer to the prevention of the spread of an infectious illness through vaccination (to confer immunity) of a specified proportion of the population. The key issue here is that for the disease to spread, an infectious agent needs to find susceptible (non-immune) people to infect. If it can’t, the chain of infection is interrupted and the amount of disease in the population falls. The key benefit of herd immunity is that those who are most vulnerable to severe disease and who cannot get the vaccination are in fact protected by the rest of the community who do get vaccinated.
“How many people need to be vaccinated to achieve herd immunity varies from disease to disease, depending on its contagiousness. For example, measles, one of the most infectious diseases known to man, needs approximately 95 per cent of the population to be vaccinated. It has been suggested that we would need about 70 per cent of the population to be immune to COVID-19 to confer herd immunity to the population.” —Associate Professor Hussan Vally, Epidemiologist and Senior Lecturer in Public Health at La Trobe University (HV)
“Herd immunity occurs when the number of people immune to infection in a population is sufficiently large to prevent infection of the non-immune people. For example, let’s say we have a disease for which an individual introduced into an entirely susceptible population infects two new people during their entire infectious period. Assuming recovery from infection leads to immunity, then the number of immune people in the population steadily grows. As the epidemic progresses, more of an individual’s contacts will be immune, making it harder to pass the infection on to new people. When an infected individual is only able to, on average, infect less than one individual the epidemic will die out. This occurs because as an infectious individual recovers since they infected less than one other person, there will be fewer infectious individuals remaining. So herd immunity (often generated by vaccination, rather than infection) can lead to a disease dying out “–Dr Trish Campbell is a Research Fellow at The Peter Doherty Institute for Infection and Immunity (TC)
“Herd immunity protects those who cannot mount an immune response or those in whom immunity will not work, usually in the context of a vaccinated population, rather than after natural infection. For some infections, 95% of the population needs to have been vaccinated to provide herd immunity.”–Professor Ian Henderson is the Director of the Institute for Molecular Bioscience at The University of Queensland. He is a Professor of Microbiology, and founder and former Director of the UK’s largest Microbiology/Infection institute, the Institute of Microbiology and Infection (IH)
“Herd immunity is something we rely on for a vaccine – not for a naturally occurring virus. This is particularly the case for a virus that is novel, and one that we have limited (but evolving) understanding of its epidemiology, and the strength of the immune response that it induces in infected individuals.
“Herd immunity is the reliance on, and the ability of, a vaccine to induce successful immunity in a threshold level of the population – such that when natural infection, or epi/pandemic strikes, a large proportion of the population will be immune and thus protected. This will limit the spread of the infection throughout the community.
“The threshold level of immunity differs for different viruses. The recent outbreaks of measles infections in various countries is often (and very likely) attributed to reductions in herd immunity, resulting from fewer people being vaccinated. In this case, the threshold for herd immunity against measles has been calculated to be 95 per cent; ie 19 out of 20 people need to be vaccinated in order to prevent unvaccinated people being infected.”–Professor Nikolai Petrovsky, is a Professor in the College of Medicine and Public Health at Flinders University. He is also Research Director, Vaxine Pty Ltd (NP)
Could we have a comment on the approach currently taken by the UK Government to allow the virus to spread and engineer herd immunity in the population?
“We do not know what the level of herd immunity that is going to be required to protect the broader community against COVID19. Until this is known and until immunity is elicited more broadly by a vaccine, relying on herd immunity to prevent or slow down this pandemic is not a good strategy.” (NP)
“In the case of COVID-19, we have yet to establish what proportion of the population needs to have been infected, and recovered, to cease transmission of the virus amongst the population. However, worst-case scenario estimates suggest that over 80% of the population would need to be naturally infected and recovered to cease transmission between people.
“The key point about herd immunity, which many have interpreted in a different manner here, is that the protected population provide a shield to reduce the transmission of the virus to the vulnerable and those who cannot clear the infection. We experience this in our day to day lives, as it helps protect us from diseases like measles.
“Using a conservative case fatality rate of 1%, this could result in approximately 500,000 deaths in the UK; this could be reduced if the at-risk populations, the elderly and those with comorbidities, were to isolate themselves throughout the pandemic.” (IH)
“Transmission of infectious diseases is different in different settings, and every government will put their own measures in place based on their priorities and the information that they have available. Rather than speculating on why the UK has introduced the measures they have introduced, I’d encourage interested parties to refer directly to the Public Health England government website for a full understanding of the measures that have been put in place.” (TC)