As to the date of April 17, 83 million of people in US, or more than 26% of US population, has been fully vaccinated. With so many people are vaccinated, one expects that the new cases of Covid-19 infection would be steadily decreased. It is surprised to many that the 7-day average cases are still in the higher 60,000. What number should be considered “normal” infection rate at this point of time and how should the new cases be compared before and after the mass vaccination?
1. Location, location, and location
Throughout the pandemic, some states had wider spread infections than the other states. Even within the states, some counties had higher number of cases than the neighboring counties. For example, the table below lists the ten states with lowest and highest infection rates. They are all over the map from the north to the south and from the east to the west.
It is complex to understand the prevalence of the COVID infection in a particular population. It may relate to many factors including geography, population demographics, government policies, social behaviors, and economic activities of the region. Therefore, it is difficult to draw conclusion by comparing the data from North Dakota from the data from Hawaii. It is most sensible to compare the numbers within a particular population before and after vaccination.
2. A “fair” number of new infections in each state
After more than 400 days into the pandemic, the experts project that the new cases should have reached a plateau, albeit at different levels in different geographic locations. As shown in the graph below, the plateau would be further lowered with the rapid rollout of the national vaccination program.
Sudden disappearance of the COVID has been scientifically rebutted as a wishful thinking. The virus appears to remain in the society in various strains in foreseeable future. Humans need to remain to be guarded and guided for a quite long while. Yet, the question is still “how many new cases are too many”. How should we gauge the progress of the war against COVID? The best way, in my opinion, is to compare the new cases in present days against that in previous year in each locality based on known facts and solid data including population size, infection rate from the beginning of the pandemic to the present day, and percentage of fully vaccinated population. By using the reported “breakthrough” rate of vaccination (10%), one is able to estimate a “fair” daily new case number as a baseline and compare the real new cases (typically use 7-day rolling average) with the estimated number. The ratio of actual to the calculated number may provide us some sense of “going better or “something wrong”. The following table lists calculated vs. actual new cases in all 50 states plus Washington DC area.
3. The states in east coast generally had higher numbers
In the table above, you can notice that there are two groups of states with the ratio of “actual to calculated” larger and smaller than 1.0 (in red and green). It is interesting to note that up to April 17 there are 25 states are in red and 25 states in green, exactly 50/50. It is also notifiable that situation in most of the states in the east coast (except South Carolina and Georgia) are unsatisfactory.
4. Still too few vaccinated
Since only less than 30% of population were vaccinated (until April 17), there is not much correlation between vaccination rate and the ratio of actual to calculated cases.
5. No strong correlation between infection rate and new cases after mass vaccination
Some news reports suggest that the resurging new cases in some states may be resulted from the lower infected population. The following chart indicates some correlation but not very strong one, especially in the cases of Michigan and Maine. Again, as we learned from last 13 months, the causation of prevalence of the COVID infection is multi-factored at the best and fluid at the worst.
