Our findings suggest that a phased relaxation of the lockdown in NEL is necessary to avoid a potential secondary COVID-19 wave later this year and not exceed the acute bed capacity in the region. Good compliance with social distancing measures and a maximum of 5-6 daily contacts per person on average, equivalent to a 45%-55% reduction in pre-COVID-19 average daily contacts, is necessary to keep the virus suppressed and keep the reproduction number R below 1 for the rest of this year, across all nine scenarios modelled, varying the infectiousness period and proportion of symptomatic infections.
Our results suggest that lockdown is a highly effective strategy in reducing infections and mortality, and that lifting of lockdown fully in the near term would likely lead to a resurgence of cases and a secondary COVID-19 peak, as shown by other modelling studies [13-17].
We find that if the average daily contact rates per person increase to 7-8, while a secondary COVID-19 wave will occur, the increased number of hospitalisations will remain within the acute bed capacity of the local health and care system. However, such scenarios are highly undesirable, leading to multi-fold increases in the numbers of cases, hospitalisations, discharges and deaths. As seen during the primary epidemic wave, a surge in COVID-19 hospitalisations can lead to severe disruption of the health and care system leaving patients unable to receive the care they require, with elective procedures postponed or cancelled, and likely avoidance of attendance due to fears around infection leading to an increase in excess deaths . Furthermore, the infection risk to staff of having a significant proportion of hospital capacity used by COVID-19 patients places immense burden on the local health and care system. Hence, although we find that such scenarios of increased social contact are within certain operational limits, they have many negative consequences and should be avoided.
Furthermore, the analysis shows the sensitivity of the epidemic to the degree of social contact, with a relatively small increase in average social contact leading to very much worse outcomes in terms of public protection and stress to the health and care system. We note here, as discussed in more detail further in this section, that our model does not account for the varying level of risk of COVID-19 on different segments of the population, whose ability to safely engage in social contact will vary, e.g. comparison of lower-risk population such as children vs. older generations. Furthermore, the relatively broad definition of a contact does not capture the significant differences in the probability of a contact spreading infection, depending on factors such as household composition, location and contact duration. While there is insufficient data on the contact duration necessary for infection to spread, CDC use an operational definition of more than 15 minutes in their guidance on exposure to COVID-19 . It is unknown what proportion of contacts recorded in literature surveys meet this narrower criteria, however the number of these ‘higher-risk’ contacts is likely to be lower than the overall number of daily contacts. Our population average social contact parameter, c, does not attempt to capture these levels of nuance. Nevertheless, this work further highlights the need for careful and strategic relaxing of social distancing in order to control future COVID-19 outbreaks.
The pertinent question in the UK is when and how social distancing measures might be fully relaxed and whether we are prepared to reopen schools alongside society in September . Our findings suggest that, if some level of social distancing remains in place, with daily contacts at most 45-55% of that pre-COVID-19 depending on the assumed level of infection that is asymptomatic, a potential second wave would be much less severe. Although previous studies have modelled the potential impact of social distancing on viral spread [14-16], our study is the first to quantify the average number of daily contacts per person required for viral prevention and control in a setting in the UK later this year. We illustrate that small changes to the current social distancing measures would allow hospitals and ICUs to operate within capacity. However, any increase in daily contacts above an average of 6 is likely to induce a second wave and over 8 daily contacts on average would exceed the capacity of acute care.
Ongoing surveys on a representative sample of UK adults about their contact patterns on the previous day, by colleagues at LSHTM suggest that the number of daily contacts has reduced 73% with the imposed lockdown measures . More recent data reveal that although there was a small increase in the average number of contacts per person per day in the first two weeks of July, with the reopening of non-essential business from July 04, 2020, to around 4 contacts per person per day (personal communication with authors of ), this still remains below the limit of 6 that we suggest as necessary to avoid a secondary wave. Hence people remain cautious as society reopens and our findings suggests this needs to remain in place in future.
The measures suggested by our findings to control the spread of COVID-19 later this year and prevent the NEL health care system from exceeding acute bed capacity are in line with current UK policy . These measures are avoiding large gatherings, and avoiding close contact with more than six people per day. The recent introduction of phased relaxation of lockdown measures, such as reopening of schools and businesses, are important to protect education and the economy. However, since there are still infections present, it is important to keep tracking the epidemic trends and react in a timely way to any future surge, as has been the case in other countries . In particular, close attention should be paid to monitoring population groups with unique risks such as those living in intergenerational and overcrowded households, where people with a lower risk of COVID-19 complications mix with those who have greater COVID-19 risk levels.
While lockdown strategies can suppress the virus, reopening of society is important to protect the economy. Maintaining the balance between saving lives and saving livelihoods is crucial . It is also important to allow people to maintain important social links more easily, particularly where individuals are reliant on public transport and other more shared spaces to do so. Phased reopening of society, with preparedness to react quickly if the epidemic metrics start to surge are crucial over the next few months as we plan for a possible second wave. Our results give quantification on the level of compliance with social distancing that is necessary to prevent a potential future secondary wave later this year.
The work we present here has some limitations. Our model does not include granulated population structure. We do not consider age stratification and the associated risks of different age groups. We do not consider contact patterns characteristic of population groups with different employment types, household compositions or social behaviours. We have used a single parameter to describe the average daily contact rate rather than a contact matrix representing mixing within and between population groups. Hence the amount of social contacts per person per day derived here as necessary for future outbreak control is an average value for the entire population. This means our result of 5-9 contacts as the limit for our system is not a hard line for all individuals and will vary depending on individual COVID-19 risk. For example, with reopening of schools, school-age children returning to school may have more than 8 contacts per day while having lower risk of COVID-19, while older generations are at much higher risk and so may remain shielded with contacts well below 8. We also note that neglecting population structure can overestimate the size of outbreaks . This is due to the susceptible subpopulations of different groups actively shielding or becoming depleted. Furthermore, the broad definition of a contact means that all contacts are not equal in terms of probability of spreading infection. As a result, we expect our study to underestimate the average contact rate that is safe for avoiding a second wave.
While we have made every effort to characterise the pandemic in a way that resembles that of the UK, some of the parameters we have used are from a variety of sources across different settings within the published literature. Since the purpose of the study was a large scale sensitivity analysis on the impact of the daily contact rate on mitigating a secondary pandemic wave, such parametrisation is sufficient. We did not consider other control measures that might decrease the reproduction number, e.g. shielding of vulnerable population groups. We assumed that isolation of cases and contacts is completely effective and that all symptomatic cases are eventually reported. We also assumed that contact is required for transmission of COVID-19 between two individuals while indirect transmission via fomites might be possible. While relaxing these assumptions may affect outcomes such as the size of a potential secondary peak quantitatively, we don’t expect these to change the overall message of our work.
We note that our study only looks at contact rate as the main driver of transmission of the virus and does not account for behavioral changes that alter transmission in some other way. For example, if people follow guidance on social distancing and mask wearing even when socially mixing, this may reduce the transmission probability even as a given level of contact is maintained . We have not considered the policy of compulsory face coverings imposed in England from 24th July. But we note that if we assume 45% mask efficacy with 70% compliance, resulting in a 30% overall reduction in risk, then the number of effective contacts could be 30% higher than the values reported here. Incorporating this and other non-pharmaceutical interventions within the model is something we plan to explore in future. Additional, complementary work on this is ongoing by some of the authors, focusing on assessing the impact of this policy combined with reopening schools and society from September 2020 and with ongoing test-trace-isolate strategy on the COVID-19 epidemic next year.
The methodology we have used here can easily translate to other settings. NHS Right Care  have a tool that uses demographic factors (deprivation, age, population and ethnicity) to compare different Clinical Commissioning Groups (CCGs) and provides a ‘nearest-10’ comparator group for each CCG. By identifying the CCGs that are similar to those in NEL, future work can compare COVID-19 deaths and hospitalisations across such CCGs and use these to re-calibrate the model. This will allow us to explore whether the compliance with social distancing that we are suggesting here is applicable to similar CCGs.
In summary, we show that phased relaxing of the lockdown in NEL is necessary to avoid secondary COVID-19 wave and not exceed the acute bed capacity in the health and care system. Good compliance with social distancing measures, with a maximum of 5-6 daily contacts per person on average (i.e. a 45-55% reduction in pre-COVID-19 average daily contacts), is necessary to keep COVID-19 suppressed and keep R below 1.