A question that is going to come up more and more is how much can we relax our behavior once we as individuals are vaccinated. It is a complicated question and I have seen varying opinions from smart people, but I will take a stab at answering the question here. There will be people at either extreme who won't change their behavior, but this is for those in the middle who are looking for some guidance. This might get a bit long, but it is a nuanced discussion - consider yourself warned.
The CDC has put out some messaging recently that could be confusing. While they are continuing to recommend people not change their behavior after vaccination, they recently said that people who are fully vaccinated don't have to quarantine. When taken at face value, these recommendations seem to contradict each other, and the first recommendation might dissuade people from getting vaccinated. So does getting vaccinated decrease your risk of COVID enough to warrant a change in behavior? That answer to that question requires many variables.
The variables that come into play are similar to those before vaccination, but vaccination changes some of the values. These include:
1. Community transmission - this factors into the risk that any one person you will come in contact with has COVID - The closer this gets to 0, the less the other factors matter
2. The overall riskiness of the gathering - how large is it? what will you be doing? are those you are gathering with vaccinated?
3. The prior behaviors of those you are gathering with
4. The effectiveness of the vaccine - does it prevent severe disease? mild disease? asymptomatic disease? transmission?
5. Your personal risk tolerance
What we know about the vaccine - Based on research studies and a recent 'real-life' study from Israel, these vaccines are very effective at preventing severe disease and symptomatic disease. They are 95% effective at preventing symptomatic disease and there have been very few severe COVID cases in those vaccinated. I think the Israel study showed for over 600,000 vaccinated individuals, only 608 were infected and 0 died.
We we don't know but can presume - The vaccine will likely decrease the rate of transmission. We know asymptomatic individuals are less likely to transmit the infection and we know that the vaccine significantly decreases symptomatic COVID, so it would stand to reason that this will decrease transmission to some extent, but the exact level is not known. My personal guess is that it will significantly decrease the risk of transmission, but we can't yet say that for certain.
So what is the real-life application of this once you are vaccinated? It depends on the scenario. Here are my thoughts:
A small group of fully vaccinated friends - It is highly unlikely that there would be any transmission among the group, especially if any other mitigation efforts take place. The risk of a fully vaccinated person having asymptomatic infection and passing it along to another fully vaccinated person would be exceedingly low. The risk of that 2nd vaccinated person having a serious case of COVID would have to be approaching 0.
The common question: 2 unvaccinated parents with 2 kids in daycare/school, wanting to know about visiting their vaccinated parents/grandparents. If you look at the numbers, the risk of the grandparents getting severe COVID is low. I think the following math is correct. At the current cases/100K rate in Iowa, assuming we detect 1/2 of cases, the risk that any one randomly selected unvaccinated person has COVID is ~0.25% (rough estimate), making the total risk of 1 of those 4 having it being 1%. Risk of transmission to household contacts from prior studies is up to 15% (usually lower - could be much higher with new variants). Now assume 95% decrease in risk of getting COVID due to the vaccination, and the risk of each individual grandparent getting symptomatic COVID would be 1% * 15% * .05% x 2 (accounting for the fact that either grandparent could get it). My math shows a risk of 0.015% for one of the grandparents getting symptomatic COVID, or 1.5 in 10,000. The risk of getting severe COVID is likely much lower based on the low number of severe cases seen in the trials and replicated in Israel.
Now if you flip that question on it's head and ask what is the risk of the grandparents having asymptomatic infection and transmitting it to their children or grandchildren, we have to make an assumption of how much the vaccine will decrease risk of transmission. If we conservatively say 50% decrease in transmission (which is likely way too low) and no effect on decreasing asymptomatic infection (likely not true), the risk would still be in the 10-20/10,000 range. If the vaccine does better than that with decreasing transmission and decreasing asymptomatic infections, those numbers would be much lower. If we are talking otherwise young and healthy people, their risk of severe disease would be extremely low as well.
My personal question: 2 vaccinated adults with 2 unvaccinated young children visiting vaccinated parents. The main risk here is the unvaccinated kids (who are at daycare) transmitting it to their vaccinated grandparents. However, using the assumptions above, the risk of the grandparents getting symptomatic COVID from their unvaccinated grandchildren would be 7.5 in 100,000 (0.5% that either kid has it, 15% household transmission risk, 95% reduction in risk for the grandparents from being vaccinated). Again, that is just the risk for any symptoms, and the risk of severe disease is significantly lower than that.
What not to do: All of the above examples are small gatherings, and therefore the minuscule risk of transmission wouldn't likely contribute to many downstream infections that could affect additional (potentially unvaccinated or high risk) people. I would still avoid large gatherings, gatherings with high-risk unvaccinated individuals, or high risk activities, etc until we see a significant decrease in community transmission, but small, low-risk gatherings with vaccinated people are reasonable to consider depending on your risk tolerance.
Anyone who has been following my intermittent posts throughout all of this knows that I have been on the risk-averse side of these discussions. However, COVID risk isn't going to be 0 anytime soon, and as vaccination rates continue to increase and data of effectiveness start to accumulate, we need to start thinking about how to move forward with the next stage of the pandemic. These numbers take a lot of assumptions into account, but at least provide a sense of what risk we are talking about. Changes that could affect these calculations include new data that will come in regarding transmission after vaccination, an overall change in community transmission rates, the emergence of variants (increasing transmissability or decreasing vaccine effectiveness), etc.
Cue tl;dr and 'i was told there would be no math'. Thanks to all of those who made it this far for listening.
The CDC has put out some messaging recently that could be confusing. While they are continuing to recommend people not change their behavior after vaccination, they recently said that people who are fully vaccinated don't have to quarantine. When taken at face value, these recommendations seem to contradict each other, and the first recommendation might dissuade people from getting vaccinated. So does getting vaccinated decrease your risk of COVID enough to warrant a change in behavior? That answer to that question requires many variables.
The variables that come into play are similar to those before vaccination, but vaccination changes some of the values. These include:
1. Community transmission - this factors into the risk that any one person you will come in contact with has COVID - The closer this gets to 0, the less the other factors matter
2. The overall riskiness of the gathering - how large is it? what will you be doing? are those you are gathering with vaccinated?
3. The prior behaviors of those you are gathering with
4. The effectiveness of the vaccine - does it prevent severe disease? mild disease? asymptomatic disease? transmission?
5. Your personal risk tolerance
What we know about the vaccine - Based on research studies and a recent 'real-life' study from Israel, these vaccines are very effective at preventing severe disease and symptomatic disease. They are 95% effective at preventing symptomatic disease and there have been very few severe COVID cases in those vaccinated. I think the Israel study showed for over 600,000 vaccinated individuals, only 608 were infected and 0 died.
We we don't know but can presume - The vaccine will likely decrease the rate of transmission. We know asymptomatic individuals are less likely to transmit the infection and we know that the vaccine significantly decreases symptomatic COVID, so it would stand to reason that this will decrease transmission to some extent, but the exact level is not known. My personal guess is that it will significantly decrease the risk of transmission, but we can't yet say that for certain.
So what is the real-life application of this once you are vaccinated? It depends on the scenario. Here are my thoughts:
A small group of fully vaccinated friends - It is highly unlikely that there would be any transmission among the group, especially if any other mitigation efforts take place. The risk of a fully vaccinated person having asymptomatic infection and passing it along to another fully vaccinated person would be exceedingly low. The risk of that 2nd vaccinated person having a serious case of COVID would have to be approaching 0.
The common question: 2 unvaccinated parents with 2 kids in daycare/school, wanting to know about visiting their vaccinated parents/grandparents. If you look at the numbers, the risk of the grandparents getting severe COVID is low. I think the following math is correct. At the current cases/100K rate in Iowa, assuming we detect 1/2 of cases, the risk that any one randomly selected unvaccinated person has COVID is ~0.25% (rough estimate), making the total risk of 1 of those 4 having it being 1%. Risk of transmission to household contacts from prior studies is up to 15% (usually lower - could be much higher with new variants). Now assume 95% decrease in risk of getting COVID due to the vaccination, and the risk of each individual grandparent getting symptomatic COVID would be 1% * 15% * .05% x 2 (accounting for the fact that either grandparent could get it). My math shows a risk of 0.015% for one of the grandparents getting symptomatic COVID, or 1.5 in 10,000. The risk of getting severe COVID is likely much lower based on the low number of severe cases seen in the trials and replicated in Israel.
Now if you flip that question on it's head and ask what is the risk of the grandparents having asymptomatic infection and transmitting it to their children or grandchildren, we have to make an assumption of how much the vaccine will decrease risk of transmission. If we conservatively say 50% decrease in transmission (which is likely way too low) and no effect on decreasing asymptomatic infection (likely not true), the risk would still be in the 10-20/10,000 range. If the vaccine does better than that with decreasing transmission and decreasing asymptomatic infections, those numbers would be much lower. If we are talking otherwise young and healthy people, their risk of severe disease would be extremely low as well.
My personal question: 2 vaccinated adults with 2 unvaccinated young children visiting vaccinated parents. The main risk here is the unvaccinated kids (who are at daycare) transmitting it to their vaccinated grandparents. However, using the assumptions above, the risk of the grandparents getting symptomatic COVID from their unvaccinated grandchildren would be 7.5 in 100,000 (0.5% that either kid has it, 15% household transmission risk, 95% reduction in risk for the grandparents from being vaccinated). Again, that is just the risk for any symptoms, and the risk of severe disease is significantly lower than that.
What not to do: All of the above examples are small gatherings, and therefore the minuscule risk of transmission wouldn't likely contribute to many downstream infections that could affect additional (potentially unvaccinated or high risk) people. I would still avoid large gatherings, gatherings with high-risk unvaccinated individuals, or high risk activities, etc until we see a significant decrease in community transmission, but small, low-risk gatherings with vaccinated people are reasonable to consider depending on your risk tolerance.
Anyone who has been following my intermittent posts throughout all of this knows that I have been on the risk-averse side of these discussions. However, COVID risk isn't going to be 0 anytime soon, and as vaccination rates continue to increase and data of effectiveness start to accumulate, we need to start thinking about how to move forward with the next stage of the pandemic. These numbers take a lot of assumptions into account, but at least provide a sense of what risk we are talking about. Changes that could affect these calculations include new data that will come in regarding transmission after vaccination, an overall change in community transmission rates, the emergence of variants (increasing transmissability or decreasing vaccine effectiveness), etc.
Cue tl;dr and 'i was told there would be no math'. Thanks to all of those who made it this far for listening.
