In this post we will look at the number of cases and number of deaths due to Covid-19 in England, and we will use these numbers to estimate a few things:

  • The approximate number of cases that actually occured during the first wave (Winter and Spring of 2020)
  • The mortality rate (or rather, the number of people dying vs the number of positive cases)
  • The number death rate for the next few weeks based on the number of new cases over the last couple of weeks.

Importing data

We will grab the data on the number of cases and deaths for each English region and also do some cleaning and feature engineering.

from uk_covid19 import Cov19API

import pandas as pd
import altair as alt
import numpy as np 

filter_all_regions = [
structure_deaths = {
    "date": "date",
    "areaName": "areaName",
    "newCases": "newCasesByPublishDate",
    "newDeaths": "newDeathsByDeathDate"

eng_deaths = Cov19API(filters=filter_all_regions, structure=structure_deaths).get_dataframe().fillna(0)

eng_deaths['date'] = pd.to_datetime(eng_deaths['date'], format='%Y-%m-%d')
eng_deaths.sort_values(['areaName', 'date'], inplace=True)

eng_deaths['weeklyDeaths'] = eng_deaths.groupby(by='areaName')['newDeaths'].rolling(7).sum().reset_index(drop=True).fillna(0)
eng_deaths['weeklyCases'] = eng_deaths.groupby(by='areaName')['newCases'].rolling(7).sum().reset_index(drop=True).fillna(0)
eng_deaths['mortalityEstimated'] = 100 *(eng_deaths.groupby(by='areaName')['weeklyDeaths'].shift(-14))/eng_deaths['weeklyCases']

Next we do the same for the whole of England.

filter_england = [
full_eng_deaths = Cov19API(filters=filter_england, structure=structure_deaths).get_dataframe().fillna(0)

full_eng_deaths['date'] = pd.to_datetime(full_eng_deaths['date'], format='%Y-%m-%d')
full_eng_deaths.sort_values(['areaName', 'date'], inplace=True)
full_eng_deaths['newDeaths'].iloc[-1] = np.nan
full_eng_deaths['newDeaths'].iloc[-2] = np.nan
full_eng_deaths['newDeaths'].iloc[-3] = np.nan
full_eng_deaths['laggedNewDeaths'] = full_eng_deaths['newDeaths'].shift(-7)
full_eng_deaths['estimateCasesFromDeaths'] = full_eng_deaths['laggedNewDeaths'] * 50
full_eng_deaths['estimateDeathsFromCases'] = full_eng_deaths['newCases'] * 0.02
/opt/hostedtoolcache/Python/3.7.12/x64/lib/python3.7/site-packages/pandas/core/ SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame

See the caveats in the documentation:
  self._setitem_single_block(indexer, value, name)

Plotting the data

We first start by looking at the number of deaths in each English region since the beginning of march, then estimate the mortality rate (rate of deaths per positive case) in each region. We then move on to look at the data for the whole of England.

Plotting: English regions

bars = alt.Chart(eng_deaths.query("date >= '2020-03-01'")).mark_bar().encode(
    x=alt.X("yearmonthdate(date):T", axis=alt.Axis(title='Date')),
    y=alt.Y("weeklyDeaths:Q", axis=alt.Axis(title='Weekly number of deaths')),

bars.facet(alt.Column('areaName', title='Region'), columns=1).properties(title='Weekly number of deaths in each region')

bars = alt.Chart(eng_deaths.query("date >= '2020-07-07'")).mark_bar().encode(
    x=alt.X("yearmonthdate(date):T", axis=alt.Axis(title='Date')),
    y=alt.Y("mortalityEstimated:Q", axis=alt.Axis(title='Implied estimated mortality')),

bars.facet(alt.Column('areaName', title='Region'), columns=1).properties(title='Number of deaths as a percentage of number of cases')