Worldwide, cases have also dropped more than 30 percent since late August. “This is as good as the world has looked in many months,” Dr. Eric Topol of Scripps Research wrote last week.
These declines are consistent with a pattern that regular readers of this newsletter will recognize: Covid’s mysterious two-month cycle. Since the Covid virus began spreading in late 2019, cases have often surged for about two months — sometimes because of a variant, like Delta — and then declined for about two months.
Epidemiologists do not understand why. Many popular explanations, like seasonality or the ebbs and flows of social distancing, are clearly insufficient, if not wrong. The two-month cycle has occurred during different seasons of the year and occurred even when human behavior was not changing in obvious ways.
I'm seeing very little talk of what seems to me a likely culprit; Herd immunity. With just how infectious the Delta variant is, and how many adults are vaccinated, I wouldn't be surprised if 90%...
I'm seeing very little talk of what seems to me a likely culprit; Herd immunity. With just how infectious the Delta variant is, and how many adults are vaccinated, I wouldn't be surprised if 90% of the adult US population has some immunity to the virus at this point.
Prior waves were with seemingly less infectious variants. They also predated wide availability of vaccines, and were met with stronger social distancing measures as their numbers increased.
Maybe I have it all wrong. I'd like to see what an actual epidemiologist has to think.
I've made the same assumption several times during the pandemic, but seem to have been proven wrong each time, especially when I've assumed that at least my locale has reached some level of local...
I've made the same assumption several times during the pandemic, but seem to have been proven wrong each time, especially when I've assumed that at least my locale has reached some level of local herd immunity. Just like this article states here in west Georgia (US state, not the country) we've seen a significant dip in the last couple of weeks. We just came off a high of 92% ICU usage last week and are down to 66%. This particular area is deeply Red, having voted for Trump at a rate of about 75% of the county, and hasn't taken COVID even moderately serious since the very beginning (currently sitting at 21% vaccination rate). So I've repeatedly figured that everyone who can get it has already had it. But I've been proven wrong each time.
I'm curious if anyone else has explanations for the 2-month cycle that they refer to as mysterious. It seems to me that it is a complicated interaction between social human behavior (complacency...
I'm curious if anyone else has explanations for the 2-month cycle that they refer to as mysterious.
It seems to me that it is a complicated interaction between social human behavior (complacency with the state of affairs can turn to fear of the disease, resulting in further distancing), weather (periods of extreme weather like hurricanes and rain causing people to congregate, and the opposite let's people outside), there is a portion of the population that is more exposed/at frequent risk (unvaccinated, in-person workers, etc.), and the steadily increasing vaccination rate. Plus boosters!
I keep trying to explain this to a family member, but get responses like "the epidemiologist just don't know" or "no one knows why!"
Anyways I'm curious if I'm missing something that makes this seem more mysterious than it is.
If you look at the all-time chart - https://covid.cdc.gov/covid-data-tracker/#trends_dailycases You can see troughs at March 2020 (Starting point) June 2020 September 2020 March 2021 June 2021...
I don't know if the periodicity is really as regular as the article suggests. I think each of these peaks and troughs could have independent explanations. One of the troughs (June 2021) can be explained by vaccine availability. The following peak can be explained by the Delta variant. In 2020 the US had a massive peak thanks to Thanksgiving/Christmas travel. I don't think there's some grand universal explanation for the function. We've only had a few cycles so far so it's easy to kid yourself and draw some conclusions from the limited number of cycles.
I hadn't thought about how the different peaks were really under different circumstances - very good point. I also think there's complexity/obscurity in a national graph, since different regions...
I hadn't thought about how the different peaks were really under different circumstances - very good point.
I also think there's complexity/obscurity in a national graph, since different regions of the country are getting affected at different times and extents. All around, many many variables.
Anecdotally that was my thought as well -- you could probably track somewhat accurately the current COVID news headlines around here just by monitoring mask usage. However, I guess these 2 month...
Anecdotally that was my thought as well -- you could probably track somewhat accurately the current COVID news headlines around here just by monitoring mask usage. However, I guess these 2 month cycles also occur in places where the majority of people don't take precautions? So seemingly there is something else going on.
It seems like there were some interesting attempts to do predictions earlier in the pandemic? They didn’t work for calling a peak or predicting whether there would be another wave, but I think...
It seems like there were some interesting attempts to do predictions earlier in the pandemic? They didn’t work for calling a peak or predicting whether there would be another wave, but I think that’s too much to ask. You can do okay by assuming that current trends continue for a few weeks, though.
So I think calling it a two-month cycle is too specific. Instead I think of it as “waves don’t last forever so within weeks there will be a peak.”
I'm seeing very little talk of what seems to me a likely culprit; Herd immunity. With just how infectious the Delta variant is, and how many adults are vaccinated, I wouldn't be surprised if 90% of the adult US population has some immunity to the virus at this point.
Prior waves were with seemingly less infectious variants. They also predated wide availability of vaccines, and were met with stronger social distancing measures as their numbers increased.
Maybe I have it all wrong. I'd like to see what an actual epidemiologist has to think.
I've made the same assumption several times during the pandemic, but seem to have been proven wrong each time, especially when I've assumed that at least my locale has reached some level of local herd immunity. Just like this article states here in west Georgia (US state, not the country) we've seen a significant dip in the last couple of weeks. We just came off a high of 92% ICU usage last week and are down to 66%. This particular area is deeply Red, having voted for Trump at a rate of about 75% of the county, and hasn't taken COVID even moderately serious since the very beginning (currently sitting at 21% vaccination rate). So I've repeatedly figured that everyone who can get it has already had it. But I've been proven wrong each time.
I'm curious if anyone else has explanations for the 2-month cycle that they refer to as mysterious.
It seems to me that it is a complicated interaction between social human behavior (complacency with the state of affairs can turn to fear of the disease, resulting in further distancing), weather (periods of extreme weather like hurricanes and rain causing people to congregate, and the opposite let's people outside), there is a portion of the population that is more exposed/at frequent risk (unvaccinated, in-person workers, etc.), and the steadily increasing vaccination rate. Plus boosters!
I keep trying to explain this to a family member, but get responses like "the epidemiologist just don't know" or "no one knows why!"
Anyways I'm curious if I'm missing something that makes this seem more mysterious than it is.
If you look at the all-time chart - https://covid.cdc.gov/covid-data-tracker/#trends_dailycases
You can see troughs at
I don't know if the periodicity is really as regular as the article suggests. I think each of these peaks and troughs could have independent explanations. One of the troughs (June 2021) can be explained by vaccine availability. The following peak can be explained by the Delta variant. In 2020 the US had a massive peak thanks to Thanksgiving/Christmas travel. I don't think there's some grand universal explanation for the function. We've only had a few cycles so far so it's easy to kid yourself and draw some conclusions from the limited number of cycles.
I hadn't thought about how the different peaks were really under different circumstances - very good point.
I also think there's complexity/obscurity in a national graph, since different regions of the country are getting affected at different times and extents. All around, many many variables.
Anecdotally that was my thought as well -- you could probably track somewhat accurately the current COVID news headlines around here just by monitoring mask usage. However, I guess these 2 month cycles also occur in places where the majority of people don't take precautions? So seemingly there is something else going on.
It seems like there were some interesting attempts to do predictions earlier in the pandemic? They didn’t work for calling a peak or predicting whether there would be another wave, but I think that’s too much to ask. You can do okay by assuming that current trends continue for a few weeks, though.
So I think calling it a two-month cycle is too specific. Instead I think of it as “waves don’t last forever so within weeks there will be a peak.”