Covid first appeared in Wuhan China in the fall of 2019. It hit the US via Europe in the spring of 2020. By the fall of 2020, our understanding of Covid has reached the point where there are multiple vaccines with better than 90% effectiveness in blocking infection.

In the fall of 2020, the critical issue is how to manage life and the economy until vaccines are widely available sometime in mid 2021. In the US, 10 M confirmed cases, probably around 20M infected, both asymptomatic and symptomatic. We are 10% of the way to herd immunity, which we would get to in 3-4 years at the current rate. A total of 220,000 have died. So far we have had 3 waves, with the hospitals in some counties nearing breaking point, coincident with a critical daily case count of 500-1000 per day per million. We have around 3000 hospital beds per million, with a 65% average occupancy that can rise to 100% in flu season. The Hospital Admissions seem to be roughly the same as daily case count, so the critical daily case count would be expected to be around 1000 per day per million.

COVID CHARACTERISTICS

 

Covid is a coronavirus that causes respiratory infection that spreads primarily by aerosol transmission. It is highly infectious such that when it first appeared, one infected person infected at least 5 other during the 10 days that they were infectious. For comparison this is 3x MORE infectious than flu.. Unconstrained, Covid would have run through the entire US within months, causing catastrophic collapse of the health care system.

The infection propagates by exponential growth, so it can be best understood through plots of the log of the infected population and where the growth rate can be measured as the slope of linear sections of the data.

It is also clear that infections are controlled by human behavior such as social distancing. The resulting hospitalizations and deaths are controlled by the demographics of the infected population and the skills of the health care system. 

PROGRESSION THROUGH A SERIES OF WAVES

 

The progression of the infection in the US has formed a series of "waves". The first wave primarily hit the North East (NY et al.), the second wave hit the large southern states (FL, TX, AZ, CA). The current third wave is focused on the North Central region (ND, SD, WI, ID) but most of the country is seeing increased infection, so the virus is becoming more uniformly spread across the country.

The first wave came to the US from China via Europe and arrived in New York in early 2020. Early on, the dangers of the virus were pretty clear, and the states issued social distancing guidance and then it took around a month for the infection rate to start to drop. Based on the infection levels, we can visualize a spreading pattern out from NY. Many distant states such as TX, shut down early and dodged the worst of the first wave. NY was particularly badly hit because this was a new virus, and the medics did not know how best to treat it so the hospitals were overwhelmed. The second wave seems to have been triggered by Memorial day enthusiasm across the southern states. The third wave has been centered on the North Central states, although by late October most states were seeing rising infections. This wave seems to get started coincident with the Sturgis bike rally and opening of schools. These states have NOT embraced masks or distancing. Ever since we responded to the first infection with a shutdown, followed by cycles of opening and closing, the infections rates have been controlled by behavior rather then the inherent properties of the virus. By end of Jan, most states are seeing cases dropping. 

LETHALITY

The hospitalizations and deaths are a reflection of  number of cases, the demographics of the cases, and the progress being made by the health system.  By  the end of Dec., ICU capacity is getting perilously close to the available. 

The graph shows hospital admissions and deaths have fallen relative to cases. The medics have major strides in managing the infection. In the early stages (Wave 1), hospitals in NY were maxed out and the case fatality rate was near 10%. Today it is less than 2%. For the over 70 community, it started at 30%, today it is down to 6%. The time lag between infection and death has also increased noticeably as treatments have improved

Lethality is measured by the deaths divided by cases or Case Fatality Rate (CFR). Similar to other resipiratory illnesses, Covid preys on the old and infirm.

BENCHMARKS AND COMPARISON TO OTHER INFECTIONS

Seasonal flu has a repeating annual signature with a transmission of 1.4 infections per person. Covid with 5 infections per person rises much more quickly. If a lockdown had not been instituted, the deaths would have been nearly 100,000 a day !!! The solid lines show the standard model projections without any changes in pre-Covid behavior.

LIVING WITH COVID
 

How best to live with Covid has become a terrible political football. The science on masks use, and the activities to avoid is clear. Covid is spread primarily by aerosol exposure - so close contact, indoors with poor ventilation maximises risk. Social distancing, wearing masks, meeting outdoors all minimize risk. Super-spreading events are major drivers of infections. Only 10-15% of infected people show symptoms, so there are a lot people who think they are fine, who are actually spreading the infection 

Here are some examples of useful resources.

A really interesting paper used cell phone data to correlate activities to infections in 6 major metro locations. This gives clear evidence as to risky activities.

 

TREATMENTS

There has been huge progress in finding drugs that help mange infections and in developing a vaccine. The infection starts in the lungs, but it seems to trigger an overreaction of the immune system that can cause catastrophic inflammation. Combinations of anti-virals and anti-inflammatories have made a huge impact on outcomes.

Here are summaries of a few key papers on Remdezivir, HCQ, Steroids.

VACCINES
 

Multiple vaccines are in development and 4 are in Phase 3 trials involving around 30,000 volunteers in each for 4 months. All show significant antibody reaction, early efficacy  data on 3 different vaccines is better than 90%.

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