Background
Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is the name given to the 2019 novel coronavirus. COVID-19 is the name given to the disease associated with the virus. The COVID-19 pandemic has led to radical political control of social behaviour across the world. SARS-CoV-2 is a new strain of coronavirus that has not been previously identified in humans. Following the first recorded cases of SARS-CoV-2 on the 29th January in the United Kingdom, the COVID-19 pandemic has taken a rapidly developing course with a switch by the United Kingdom (UK) Government on the 17th March from a policy of “track and containment” to “mitigation” and initiated social distancing, followed by a comprehensive population lockdown on the 23rd March. The toll on health and lives has been very significant in the UK and elsewhere in the world (1). High-risk groups, based on age and underlying comorbidities, were told to isolate themselves completely for the next 13 weeks (2,3). The rationale was to reduce the impact of the high growth phase of the pandemic on the National Health Service (NHS) with particular focus on Intensive Care Units (ICUs) and High Dependency Units (HDUs) and to keep mortality to a minimum (4,5,6).
Pandemic models forecast that with continuing progress the social lockdown would be relaxed when there is clear evidence of a downturn in infection rates and mortality. There is a trade-off here between balancing the clinical impact of the pandemic with the economic, social and longer-term healthcare impact. This includes considering the impact on diverting resources away from mainstream severe and long-term conditions within primary and secondary care, as well as recognising that the capacity of the population to maintain confinement is limited.
Testing in the very initial phases was carried out on the wider groups who had contacts with diagnosed patients. Testing capacity initiatives have been slow to appear with testing at 5,000/day at the end of March increasing to 10,000/day in April (7). As number of new cases grew and testing capacity limitation was reached testing was restricted to symptomatic hospital-based patients, and more recently as numbers have fallen and testing capacity increased to general practice presentations and NHS staff. Using the total confirmed cases as a sample of the overall levels of population infection is reasonable if the selection rules are consistently applied both over time and geography. While there may be some variations, selection for testing was being restricted during the growth phase and then increased as numbers fall. This will have first reduced and now increase the numbers of new cases identified. The direction of any error would therefore be to initially to show lower and now relatively higher infection rates.
Given the past community based 3-day doubling infection rate, there are indications that significant part of the population may already have been infected with low grade clinical or subclinical symptoms. This wider non-hospitalised population is likely to continue to grow even with the isolation and social distancing policies.
The ongoing rate of infection is determined to a large extent by the R-value of an infectious disease. The R-value is the number of people infected by one infected person during their infectious phase (8). This value is dependent on the level of local and cross-community social contacts and the proportion of the current population who have not developed immunity through previous exposure. An R-value above 2 suggests more than a doubling of people with the condition during each infectious period and an R-value below 1 is consistent with “suppression” meaning that the virus prevalence will slowly diminish.
The purpose of this paper is to briefly explore data trends from the pandemic in terms of infection rates and policy impact and draw learning points for informing the unlocking process.