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.