How long could UK cases continue to rise? And how might hospitalisations increase alongside? A thread... 1/
Despite relatively high vaccination rates compared to other countries, cases are growing and in many areas R is now above 1.5. Remember, immunity is already 'priced in' to this number - without vaccination and the social distancing still in place, R would be *much* higher. 2/
If R is 1.5 and contacts/control remain the same, then we'd need remaining part of the population who could potentially spread COVID to shrink by at least 33% before R drops below 1 & epidemic peaks. This would require additional immunity, either from infections or vaccines. 3/
If contacts were to increase and, say, R increased to 2.5, then we'd need at least 60% reduction in size of remaining group who could potentially spread infection. Again, these calculations already account for vaccination to date – and still rather far from getting R below 1. 4/
Vaccines are rolling out at fairly steady pace but epidemic increasing exponentially, which means infections will gradually outpace vaccines as source of new immunity. The question, of course, is what the impact will be before R drops below 1 and epidemic declines... 5/
Vaccines can directly reduce: the risk of infection following exposure, risk of symptoms following infection and risk of severe disease following symptoms (and can also reduce initial exposure risk in community thanks to herd immunity effects described above). 6/
If cases rising, it's symptoms->severe disease risk we're interested in. COVID admission are rising, and were infected when cases at low levels. So even if other links weakened by vaccines (less exposure, infection, symptoms), cases are translating into hospitalisations... 7/
So hospitalisations will continue to increase unless either we see a big further change in symptoms->severe disease risk (which is unlikely over such a short period), or R eventually declines below 1 (as described above). 8/
Finally, these are all calculations for UK, which has relatively high vaccination rates. The impact of Delta could be much, much worse in other countries – emphasising importance of getting vaccines to people at risk in rest of the world as soon as possible. 9/9
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