Saturday, April 4, 2020

Herd Immunity - A Quick Explanation

There has been a lot of discussion in the last few weeks of the UK Government’s original strategy towards Covid-19 – which was in summary to allow the infection to spread to create herd immunity given the fact that, based on the data being shared at the time, only around 15% of cases required hospital treatment.  Obviously, this did not correctly factor in the exponential spread of the infection.  (It is worth noting that some factors potentially skew the statistics – the general under-reporting of Covid-19 infections being one – if the infection rate is, as predicted, higher than currently shown in the statistics the death rate as a percentage may in fact fall).  This strategy has become known by the general short hand of Herd Immunity.  However this had led to some problematic reporting and some frankly dangerous statements being made - such as in this tweet from Emma Kennedy (who is a writer, actress, and television presenter, whose academic training is in corporate law, human rights law, and intellectual property law, not epidemiology, virology, immunology, or medicine).



The concept of herd immunity is not unique to Covid-19 or the coronaviruses.  In fact building herd immunity is one of the clinical purposes of vaccination programmes.  There will, in any human population, be those who cannot be vaccinated for a number of reasons – the most common being immunosuppression – either naturally or through immunosuppressant medication to treat autoimmune disorders.  These individuals cannot be vaccinated safely – however they can be protected.  Mass vaccination of those who can be vaccinated breaks the chains of transmission – allowing the unvaccinated to move freely within the population surrounded by the generally immune ‘herd’.  Thus the mass vaccinated act as a screen for those who cannot be.  This has been the strategy behind the treatment of dozens of conditions – including measles.  Herd immunity is therefore a vital method of protecting the vulnerable from dangerous, potentially fatal infections.  The use of Herd Immunity as a convenient label for the UK government’s initial strategy is causing some to equate the entire concept with this strategy and its potential impact on vulnerable populations.  In reality the clinical concept is the exact reverse of this – it is a method of protecting vulnerable populations.  Such rhetoric is not only inaccurate, but plays into the hands of one of the most dangerous ideas to have spread into society in the last two decades – the anti-vaccination movement.  This mistaken use of a label with a  clear clinical meaning plays into the hands of those who argue vaccination is in fact designed to damage society’s most vulnerable.  Herd immunity may not be appropriate for rapid spreading infections with Covid-19 with severe clinical impacts – but in other cases, it literally saves lives. 


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