Covid-19 July 21, 2021

We investigate the surge of US COVID-19 daily confirmed cases in June-July 2021.  As a function of time comparisons are made between numbers of smoothed daily COVID-19 confirmed cases and deaths,  with delta variant growth, and complete vaccinations.

N. American countries

For N. American countries (Canada, Mexico and the US) the start of the surge around July 10th is evident in both the US and Mexico (see Fig 1). It is also evident in the cumulative cases, see Fig 2 with more detail in figure 3.

Delta variant growth in US

Figs 4 and 5 show the growth of the delta variant on a linear and log scale. The growth is seen to be roughly exponential with time.

Figs 6a shows the US confirmed cases and deaths against the % of delta variant of the virus. There is a noticeable uptick in cases somewhere between 40% and 65%  delta variant. If one takes the first US reported Delta Variant (from https://www.gisaid.org/hcov19-variants/ - the GSAID initiative is an online database where scientists share genetic analyses of viral samples) of 0.1% on 4/11/21 to the 60.19%  for N America reported for 7/5/21 by https://www.gisaid.org/hcov19-variants/ then it took 85 days to go from 0.1% of cases to over 61% cases and 16 more days to get to 83% of cases being the delta variant.

Fig 6b shows the  cases and deaths vs the average date (The GSAID data gives a range of dates so we take the mid dats)

Fig 6a	Fig 6b

Impact of vaccinations in US

Looking at Fig 7 one can see the top 20 states by daily confirmed cases on 7/21/2021. The shift to weekly instead of daily reporting in Florida (FL) (also Nebraska  (NE), Iowa (IA) and South Dakota (SD) have done this) results in delayed reporting of surges (e.g. Florida updated its cases an increase in daily cases per Mpop from 320/day to 515/day on 7/23/2021 i.e. a 60% surge in reported cases) and a step function like curve. Figure 8 shows a scatter plot of COVID-19 confirmed cases vs the fraction of the population fully vaccinated on 7/22/2021, the bubbles are colored by the presidential candidate who won the state and the size of the bubble is proportional to the population, the two letter acronym for many states is included, the formula is the formula for the Pearson trendline (shown in blue dots) and the correlation R².

Fig 9 plots the US daily confirmed cases and deaths against the % population vaccinated. Fig 10 plots the daily confirmed cases and deaths versus the date. It is seen that as the % of the vaccinated population increases the daily cases and deaths decrease, however as one gets to July the confirmed cases start to increase. Looking at Fig this is when the Delta variant % start to exceed 60%.

Fig 9	Fig 10

daily The table below shows for each state in Fig 7 for whom it voted for president in the 2020 election together with the % fully vaccinated and daily confirmed cases for 7/21/2021.

Summary

• US Daily COVID-19 Confirmed cases have increased by over a factor of 3 in the 3 weeks between July 1 and July 21st.
• The US % of cases that are the more contagious Delta variant of COVID-19 was first noticed (0.1% cases) in mid-April 2013 and has increased roughly exponentially with time until by July 21st it was over 83% of the cases.
• The impact of the delta variant on an increase in cases and deaths was hardly noticeable until the delta variant cases exceeded 60%.
• The fraction of the variability of the dependent variable (Y = COVID-19 confirmed cases on 7/22/2021) that is  explained by the independent variable (X = Fraction of the US state's fully vaccinated population) is ~ 37% (the R² correlation factor)
• States that voted in 2020 for Trump (red states), in general, have lower vaccination fractions (0.42+-0.05) vs Biden blue states (0.54+-0.06), and states that voted for Trump have higher COVID-19 confirmed cases (174+-121) than states that voted for Biden (85+-62).