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What is herd immunity and how does it work?


It seems that with any newsworthy event there comes a lot of new buzzwords, and the coronavirus pandemic of 2020 has been no exception. One such term is “herd immunity”. Though not a new concept at all, it’s been getting more airtime lately thanks to discussions, ideas, and research around what to do about this scary situation. We are in uncharted waters, so as we move tentatively into the future, we’re looking at some ideas that have served us well in the past. Herd immunity is one.

The Theory Of Herd Immunity

Herd immunity is basically what the name implies: it occurs when most of the herd, tribe, or community is immune to a certain disease. This most often happens through vaccination or through a person contracting the illness and surviving it. In either of these situations, these people are now producing antibodies against the illness and are extremely unlikely to spread it.

In this theory of herd immunity, the more people there are in the herd who are immune, the lower the likelihood that a susceptible (non-immune) person would come in contact with the pathogen. So, if a critical mass is reached where a sufficient number of people are immune, the whole herd enjoys “herd immunity” whether or not they actually are immune.

Community Immunity - Does It Work?

Early in 2020, as the severity of the coronavirus pandemic became more clear, Boris Johnson offered herd immunity as a possible end-game resolution to the situation. Patrick Vallance, chief scientific adviser to the UK government, echoed that sentiment with: "Our aim is to try and reduce the peak [of the infections, broaden the peak, not suppress it completely. Also, because the vast majority of people get a mild illness, to build up some kind of herd immunity so more people are immune to this disease and we reduce the transmission."

Epidemiologist Zhong Nanshan, who has been on the front lines of the COVID-19 fight in China, spoke of the benefit of herd immunity, indicating that people who get the illness would begin producing antibodies after recovery. This makes it unlikely for them to be reinfected.

But in order for that to become a reality, around 60 percent of the population needs to be infected with the virus. Though it may be true that most people experience mild symptoms and do not require hospitalization, 60 percent of any population is a very large number. The impact of that much illness would be huge.

Herd Immunity - Experts Weigh In

As with so many other aspects of this pandemic, what the next move should be is a matter of opinion. Here are some thoughts from UK community leaders.

Prof Martin Hibberd, professor of Emerging Infectious Disease, London School of Hygiene & Tropical Medicine had this to say:

"The government plan assumes that herd immunity will eventually happen, and from my reading hopes that 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 that we can do. Another strategy might be to try to contain longer and perhaps long enough for a therapy to emerge that might allow some kind of treatment."

Prof Matthew Baylis, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool:

"Estimate predicts about 60% percent of the population would need to contract the virus to get herd immunity. And this is deeply concerning – taking the low fatality rate estimate of one percent, even 50 percent of the UK population infected by COVID-19 is an unthinkable level of mortality.

But it doesn't have to be – and it won't be – this way. By reducing the number of people that one person infects, on average, then we lower the point at which herd immunity kicks in.

From an epidemiological point of view, the trick is to reduce the number of people we are in contact with (by staying more at home), and reduce the chance of transmission to those we are in contact with (by frequent hand washing) so that we can drive down the number of contacts we infect, and herd immunity starts earlier."

Professor Peter Openshaw, former president of the British Society for Immunology and professor of Experimental Medicine at Imperial College London:

"SARS-CoV-2 is a novel virus in humans and there is still much that we need to learn about how it affects the human immune system. Because it is so new, we do not yet know how long any protection generated through infection will last.

With the novel SARS-CoV-2, the situation may be very different but we urgently need more research looking at the immune responses of people who have recovered from infection to be sure."

Dr. Erica Bickerton, the Pirbright Institute:

"Immunity to SARS-CoV-2 is not yet well understood and we do not know how protective the antibody response to this new virus will be in the long-term.

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