More good news being ignored by media
COVID-19 has been presenting as a common cold since May. So said (6 mins in) Prof Tim Spector, who runs the Zoe Symptom tracker app. Headache, sore throat and runny nose are now the three most common presenting symptoms. There is no loss of smell and cough is only the fifth most common symptom.
Rather than present this for the good news it is, the researchers chose to present it as a warning that people may fail to recognise it. If COVID-19 is becoming more mild in its symptomatology, fewer people will develop severe symptoms and fewer people will die. One of the old circulating common cold coronaviruses, OC43, was thought to have begun as a pandemic strain meaning there is a precedent for such an evolution. If this is the case it is undoubtedly good news.
Is there evidence of this effect in hospital admission data? A simple way to analyse the data is to compare total cases diagnosed in one week with hospital admissions a week later. Taking cases for the week ending 31 May and comparing them to admissions to hospital of already diagnosed cases the week ending 7 June, the hospitalisation rate was 18% for the Alpha variant and only 3.4% for the Delta variant.
It could be argued that this is because older people are not catching the Delta variant (Indian variant), yet. Indeed, models which account for the age difference purport to show that the Delta variant is more dangerous. There have been only 223 total admissions of patients diagnosed in the community since February. Is it really reasonable to conclude that the Delta strain leads to more hospital admissions by age based on such small numbers, especially when the raw data shows it leads to 1/6th of the admissions of the Alpha variant?
The overall percentage of cases that end up in hospital has fallen since the Delta variant became dominant. Furthermore, the slight rise in hospital admissions has not translated into the expected rise in total patients. This means that the length of stay for patients admitted with a positive test is shorter than it was before, again indicating good news.
Claims also continue to be made that the Delta variant is more transmissible. The best real world measure of the transmissibility of a variant is the secondary attack rate: the proportion of contacts that catch the virus from a known case. Much has been made of the higher transmission rate in the Delta variant. The transmission rate of a new variant will, by definition, be higher than the current variant. However, the transmission rate for the Alpha (UK) variant fell from 15% to 8% over the last 6 months at a fairly constant rate independent of the level of vaccination. The transmission rate for the Delta variant peaked at less than 14% and is already falling. The transmission rate need only be slightly higher than the Alpha variant for the Delta to become dominant, as it has, but the other claims about transmissibility have been overblown.
Overall there is minimal real world evidence of the Delta variant behaving in a significantly more transmissible or dangerous way and the symptomatology appears to be becoming more mild.