With England returning to a full national lockdown, calls for a different response — a so-called 'segmentation strategy' — have also reappeared. The idea behind such an approach is that a 'vulnerable' section of the population is effectively sealed off from the rest of society. Meanwhile, SARS-CoV2 is allowed to spread among the remaining population, generating herd immunity which will eventually protect the entire population.
This is the core principle of the Great Barrington Declaration, which has attracted a large amount of media attention since its inception a few weeks ago. This approach has had considerable appeal to those seeking to minimise the impact of the pandemic for a variety of reasons, be they the wider health implications of restrictions, effects on education, the economy or the like. The problem with such a conclusion is that — while those are clearly laudable aims — each would suffer should we lose control of the virus. Ultimately, the concept of segmentation and herd immunity via natural infection is flawed in several ways and is not supported by current scientific understanding.
One major problem is that identifying those in the vulnerable cohort is a logistical non-starter due to the number of underlying factors that can contribute to severe disease. This includes a considerable number of people with, for example, undiagnosed hypertension or type II diabetes. Some estimates predict that up to a third of the population could be at risk. Meanwhile, it is very likely that immunity from natural SARS-CoV2 infection is short-lived, much as we see from other human coronaviruses. We are starting to see evidence of reinfection, albeit limited at this stage, but it is important to note that the virus has only been in general circulation for less than a year. We still don't know how long immunity will last or exactly what constitutes an effective response, but the majority of studies suggest that a vaccine will be necessary to achieve population-level immunity.
Moreover, to be viable, herd immunity needs to, by definition, involve a considerable proportion of the population, estimated at approximately 70 per cent by conventional measures. We now understand that a significant number of younger and otherwise 'healthy' people in fact endure severe and long-lasting complications from SARS-CoV2 infection. Given the numbers involved, we would effectively be risking a double health crisis by allowing the virus to spread unchecked. First, the immediate impact of allowing the virus to spread throughout the population, seeing our hospitals filling up with the infected and the knock-on effects that would have on non-Covid patients. Second, the unknown long-term effects of Covid for those who contract the virus can be profound, even if they don't exhibit severe symptoms at the time of infection. This health burden could remain with us for decades, draining NHS resources; preliminary studies have pointed to long-term effects ranging from a reduction in lung capacity to cognitive impairment. To allow a strategy such as this to influence any sort of pandemic-related policy would therefore be a catastrophic mistake and it is troubling to see politicians endorsing it.
Importantly, segregation related to a herd immunity strategy should be distinguished from the policy of shielding that we saw in the spring. Shielding provided advice, logistical and also legislative support for people with health conditions which render them extremely clinically susceptible to severe Covid; a sub-population among those otherwise targeted for segregation. This support allowed people to take additional precautions without fear of losing their jobs or having to expose themselves to potentially dangerous scenarios. Critically, shielding comprised part of an, albeit now failed, suppression strategy, thereby eventually leading to the pausing of the policy in August.
The current resurgence of the virus was eminently avoidable, while the suffering endured throughout lockdown and other restrictions has seemingly been for nought. This places us in a difficult position; we now need to implement another lockdown with proper support for those shielding, particularly as the less well-off are more likely to be endangered by needing to venture out to work. Should shielding return, it must do so as part of an effective suppression strategy, complemented by effective testing and tracing, and followed by a cautious reopening of society so as not to squander — yet again — the hardship of yet more difficult and painful restrictions.