The Iron Rules of Covid Lag

Time and again, with wave after wave of COVID-19, certain observations seem eternal:

• You can’t test positive for COVID-19 until after you catch COVID-19, therefore Covid testing always lags behind the actual Covid infections, typically about 2 weeks.
• All other things being equal — masking, distancing, lockdowns — the more people that have COVID-19, the more people that will catch it from them.
• Spread is therefore exponential, growing bigger makes it grow even faster.
• Those new transmissions won’t show up until after the testing lag, so if we start mitigation now — masking, distancing, lockdowns — it won’t have a noticeable effect on infection trends for two to four weeks.
• People rarely die of Covid on the first day they test positive for Covid. With modern medical intervention, it can take days or weeks. Thus the increase in deaths always lags well behind the increase in positive tests, often by several weeks.

This has been happening since the beginning of the pandemic, and yet every time we start a wave, some pundits just don’t see it. No matter how fast infection rates are rising, they loudly proclaim that we don’t need to do anything because rates are still low. They are ignoring the lag. They are ignoring that it take weeks to have an effect that shows up in testing, so if we wait until new case rates are bad before we ramp up mitigations, things will get much worse before we see the effects of the mitigations in the testing results.

Then there are the pundits who look at the statistics and triumphantly proclaim that the death rates aren’t rising so everything is just fine. Sometimes they invent a reason. I can remember people claiming in late June of 2020 that death rates were low because all the most vulnerable people had already been infected, as if the virus somehow knew to infect vulnerable people first. Then 500,000 more Americans died.

After more than a year of such punditry, we finally have widely-available vaccines that are fairly effective at preventing severe Covid and death, and many of the most vulnerable people have taken it. That means that, for the first time ever, there’s actually a good chance this wave may not be very deadly.

But we won’t actually know for sure until we’ve waited out the lag.