Is It Safe to Go Indoors Again?

28 MAY 2021 — Covid is on the wane in the US, with case counts and deaths having dropped precipitously since the beginning of the year. How will we know when we’ve reached the point where we can safely resume our pre-pandemic levels of activity?

Every year there’s an influenza epidemic, but generally speaking people go about their ordinary lives during flu season without taking extraordinary steps to avoid infection. How does the current level of covid risk compare to that of a typical flu season?

Fatality Rate. Around 40K Americans die of influenza every year — a fatality rate of 0.1%. It’s estimated that the fatality rate for covid is 0.6% — 6 times that of the flu.

Incidence. The CDC estimates that about 40 million Americans are infected with influenza each year. Flu season lasts about 17 weeks, so during a typical week around 2.4 million Americans come down with the flu. Based on my algorithms, as well as IHME estimates, around 450K Americans were newly infected with covid this past week. So, as of this week, Americans are about one-fifth as likely to contract covid as they would be to catch influenza during the flu season.

Death Risk = Fatality Rate x Incidence. This week, the risk of an American becoming infected by covid and dying from the disease = 6 x 0.2 = 1.2 times the death risk presented by influenza during the season.

Trend. Covid infection rates are trending downward. IHME projects that, by early June, weekly new infections will drop below 400K, putting the risk of dying from covid below that of dying from influenza for a typical week of flu season.

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In sum, based on risk analysis, life in the US could return to normal levels of disease prevention as soon as early June. This relaxation of vigilance would apply to everyone, vaccinated and unvaccinated alike.

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Vaccinations. The flu vaccine usually cuts risk in half. The Pfizer and Moderna covid vaccines reduce risk to less than one-tenth of what it would be without the shots. Even the less effective J&J vaccine cuts covid risk to one-third, offering significantly better protection than flu shots. Given the current rate of infection, covid vaccines offer far greater protection against infection and death than does the influenza vaccine against flu infection and death.

Are US Covid Infections on the Rise?

8 APRIL — The US case counts have plateaued over the past seven weeks, with daily fluctuations falling well within the expected range of random variation. However, as has been well and repeatedly documented, case counts greatly underestimate the number of new infections. For several months the ratio held steady at a rate of around 2.7 new infections for every new dx test-positive. Now, however, there’s evidence to suggest that the ratio is ticking upward — which would mean that the infection rate likewise is climbing. Here’s the rationale:

Covid deaths are the most accurate indicator of covid infections, with death lagging about 3 weeks after diagnosis.

The covid fatality rate varies based on age. The older a nation’s population, the higher its fatality rate. The median age in the US is 38, with an age-adjusted fatality rate of 0.65% of covid infections.

US covid vaccines have been administered disproportionately to the older, more vulnerable people. Immunizing most of the elderly effectively reduces the average age of the US population still vulnerable to infection.

Assume that the median age of unvaccinated Americans at risk of covid infection is 36 years — 2 years younger than the overall population. The age-adjustment algorithm reduces the estimated US covid fatality rate from 0.65% to 0.55%.

Using this revised fatality rate as the basis for a revised estimate of infection rate, then over the past month there have been 3.2 new infections for each new dx test-positive case — an increase of 20 percent over the previously stable ratio of infections to cases.

These calcs imply that the plateaued daily case rate disguises a 20% higher rate of new covid infections over the past month or so. That makes sense: younger people who get infected tend to experience less severe symptoms, and so are less likely to see a doctor and less likely to be tested for the virus. The current rise in infections will almost surely exhaust itself over the next two or three months as vaccinations are made readily available to all US adults and herd immunity is approached.