Question to the Department of Health and Social Care:

To ask Her Majesty's Government what estimate of the percentage of COVID-19 cases that require mechanical ventilation was applied to the forecast modelling used to inform their decision to place England under national restrictions until 2 December; and what was the evidence base used for this estimate.

The Scientific Advisory Group for Emergency’s (SAGE) subgroup, Scientific Pandemic Influenza Group on Modelling, Operational, do not have a single estimate for asymptomatic case proportions, infection hospitalisation rates, case hospitalisation rates, infection fatality rates, or case fatality rates. Individual modelling groups use their own estimates of these metrics, which are based on a wide range of data sources, including testing data, hospital admission, intensive care unit admissions, and deaths. Their models are regularly updated to fit to the observed transmission of the disease and further details are publicly available.

The Office for National Statistics COVID-19 Infection Study has estimated that approximately 55% of those individuals who test positive do not record evidence of symptoms at or around the time of the test. This does not mean these individuals will not go on to develop symptoms or had symptoms previously.

Other SAGE evidence has shown that there is wide variation in the estimated proportion of infections that are truly asymptomatic across different studies with the rapid review providing a pooled estimate, based on 22 studies, of 28% but with very wide confidence intervals.

NHS England use data from their daily COVID-19 situation report collection from individual hospital trusts to estimate current average length of stay and the proportion who require mechanical ventilation. In the run up to the national restrictions this gave an average length of stay of 7.7 days, of which 5.5% of those would be with mechanical ventilation.

The decision to re-introduce greater restrictions from 5 November until 2 December 2020 was based on a wide range of data, not just modelling estimates. These included analysis from the National Health Service on hospital capacity, the rapidly rising hospital admissions, and deaths, and the similar second waves seen across Europe.

SAGE papers from its meetings are published in an online only format on GOV.UK.