Richard Brown: What explains the low number of Covid cases in London?

The news looks good, although some numbers may be misleading

With autumn falling and the number of Covid cases rising, there is good news for Londoners. Most affected by the first wave of infections, the capital now has some of the lowest case numbers. On October 18, of 315 English lower-level councils (unit and district councils), the ten with the lowest cases were all London boroughs (Unless otherwise noted, all data in this article was taken from the excellent government dashboard).

This is not intended to downplay the terrible effect Covid has had on London. The disease has already killed more than 20,000 people in the capital, and has had a particularly brutal impact on poorer and disadvantaged communities. Unlike March 2020 when cases shot up across the city and widespread urban escapes were predicted, you are safer from Covid today in Inner London than almost anywhere else in the UK.

This is good news, but it’s not immediately clear why the falls in London are so low. While the capital has the highest levels of antibodies latest survey by the Office for National Statistics (ONS), it also appears to have the lowest vaccination rates. The ten lower-tier English authorities with the lowest vaccination rates as of Oct. 14 were all in London and are many of the same counties that also have low rates of infection. I was wondering how we can explain this without making false claims about the effectiveness of the vaccine.

Vaccination isn’t the only way to gain immunity, so early exposure of Londoners to the virus will have made a difference. London’s cumulative case numbers are around 12.5 percent of the population, which is more than the other regions of southern England but lower than the Midlands and the north. But in the early days of the pandemic, most cases went untested and went unreported unless people got seriously ill, so the total number of cases in London was almost certainly underestimated. By July 2020, 13 percent of Londoners will be of working age were already appreciated having been exposed to the virus is twice the national average.

However, there are also questions about how to calculate vaccination rates. Most Covid statistics use the mid-2020 population estimates as the denominator, but vaccination rates use the National Immunization Management Service (NIMS) database. Notable commentators have suggested that this database, credited with helping the rapid adoption of vaccines, tends to overestimate the working-age population – especially young adults and students who are most mobile. Using ONS Half-year estimates for 2020 instead of NIMS numbers makes a big difference in vaccination rates in London, as shown in the graph below, which shows the status as of October 12th.

What does all this tell us? The first thing many of us have learned over the past 18 months is to be careful, querying statistics, asking what story to tell and if there are other stories that might fit as well, especially where they belong seem to be dramatic differences between places.

The second is why local vaccination rates are published in such a way that uptake appears artificially low in places with younger populations. This may seem trivial, or even a useful push for young people and people in communities who have vaccinating shots to get their vaccinations, but using questionable data for righteous purposes can be toxic. There are enough bizarre rumors about the effectiveness of vaccinations without it being possible to jump to the conclusion that the places with the lowest number of cases are also the places that appear to have the highest proportions of unvaccinated people.

The numbers for deaths in community areas are seven-day fall rates as of the reported date, and deaths attributed to Covid in the capital are defined as those where Covid was mentioned on the death certificate as of October 14th.

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