Here are my two-cents on hospitalizations, seasonality, and what the next couple of months MIGHT look like. I have used hospitalizations to show what is happening, since they are a very good measure of the growth in Covid-19 infections. Using daily cases can work to an extent, but there are other factors that can make the case data more messy and requires further data scrubbing to make it usable for this analysis.
I do believe, based on the curves below that there is a seasonality effect driving a lot of the infection and hospitalizations we have been experiencing. Seasonality as it relates to the US is due to the following:
1. The weather turns cold and people stay inside more. Dr. Ohl, the infectious disease physician from Baptist health discussed this a month or so ago. As he pointed out, respiratory viruses love it when people move to more inside activities during the colder months. The reasons being - reduced ventilation and airflow (airflow and ventilation are enemies to respiratory viruses) and heated spaces. Heated spaces dry out the air and viruses prefer dry air to more humid air.
2. The US has a couple of big holidays at Thanksgiving and Christmas, where a large number of people travel and move around the country. Yes, other countries have Christmas, but the US is unique in having two large holidays packed closely together on the calendar. For both of these holidays, people have a tradition of travel. The day before Thanksgiving is the number one travel day in the year for a reason.
As you can see from the chart below, the total number of people hospitalized due to Covid-19 began to increase at the current rate in late October and early November, a few weeks prior to the Thanksgiving travel period. What drove this increase? Most likely, it was the same reason we see the flu begin to rise during this period - it started to get cold enough that people moved inside and they started to seek heated spaces.
On the graph, the rate of the upward trend in hospitalizations continues as NC and the US in general go through the Thanksgiving, Christmas, and New Years holidays. These holidays and their associated travel and family/group gathering activities continue to drive infections well into the first of this year.
As Wayland has pointed out, there is a strong seasonality effect that is driving a lot of the rise in total infections. We were warned months ago by Dr. Fauci and others that this would happen and it has. At the time, they were concerned about flu layered on top of Covid-19 infections, but they were clear there would be a seasonal aspect to infection increases. PackPA is also correct in pointing out that we expected Covid-19 infections to decline in the warmer months in the late Spring and Summer and they did not decline as much as expected. While I do believe we did see a decline in late Summer due to seasonality (the data does show a decline starting in late July), it was not as much as many had hoped or expected.
Looking at flu infection charts for NC for the past several years (example shown below), the level of infection and hospitalizations peaks in early to mid-February. Since Covid-19, being an airborne respiratory virus, it does appear to be driven by the same seasonality factors. I am hopeful we will see a similar peaking and decline in roughly the same period. Combined with the increases we should continue to see in vaccinations of the population, particularly vaccinating those contributing most to hospitalizations (70% of those hospitalized are 60+), should help to reduce the level of hospitalizations in the coming weeks. I am hopeful and optimistic we will begin to see the hospitalizations peak and begin to decline by mid-February. The bad news is this - we have another 4 to 5 weeks of high hospitalizations ahead of us.
I fully recognize I am not an epidemiologist and my analysis may be totally wrong, but I wanted to provide some thoughts and insight into the data trends and why they may be happening in this way.
Daily Hospitalizations and Percentage of Covid-19 Infected Hospitalized:
NC Influenza Surveillance - 2016 through 2019:
