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I thought that this was an interesting take on the subject.
Israeli data: How can efficacy vs. severe disease be strong when 60% of hospitalized are vaccinated?
One disturbing result that has been repeated about several locations is that a high proportion of patients hospitalized for COVID-19 are vaccinated. For example, we can see from data from the the Israeli government data dashboard that nearly 60% of all patients currently hospitalized for COVID-19 (as of August 15, 2021) are vaccinated (downloaded data set and details are found at the bottom of this post). Out of 515 patients currently hospitalized with severe cases in Israel, 301 (58.4%) of these cases were fully vaccinated, meaning two doses of the Pfizer vaccine.
From this type of result in various places, I have seen tweets suggesting vaccines don't work or have lost their efficacy vs. severe disease, and I have seen other articles quote this type of figure as further evidence for the reduction of effectiveness of the vaccines in trying to justify 3rd shot boosters.
However, while these numbers are true, to quote them as evidence for low vaccine efficacy is wrong and misleading. Sometimes, with observational data there is confounding of multiple factors that can make it easy to misinterpret simple percentages like this, and the current vaccination situation in Israel brings a perfect storm of confounding factors that lead to confusion if not thought through carefully.
In particular, the key factors here that contribute to this confusion are:
1) High vaccination rates in the country (nearly 80% of all residents >12yr)
2) Age disparity in vaccinations, including
3) Nearly all older people being vaccinated (>90% of residents >50yr) and
4) The vast majority of unvaccinated being younger people (>85% of unvaccinated <50yr)
5) Older people are orders of magnitude more likely to be hospitalized with a respiratory virus than young people (residents >50yr are >20x more likely to have hospitalized serious infections than residents <50yr, and residents 90+ are >1600x more likely to have hospitalized serious infections than residents 12-15yr)
After accounting for the vaccination rates and stratifying by age groups, from these same data we can see that the vaccines retain high efficacy (85-95%) vs. severe disease, showing that when it comes to preventing severe disease, the Pfizer vaccine is still performing very well vs. Delta, even in Israel from whence the most concerning data have arisen.
( Much more at link. Charts too! )
He step-by-step walks through the data and provides links for such. Quite worthwhile to give it a skim.
The key point is to stratify data by age, otherwise one can fall to something called "Simpson's paradox".
And before the "anti-covid-vaxxers" start the attack (
), note that this author has another web page:
Overwhelming evidence now that previously infected have robust immune protection against reinfection
-- Michael
Israeli data: How can efficacy vs. severe disease be strong when 60% of hospitalized are vaccinated?
One disturbing result that has been repeated about several locations is that a high proportion of patients hospitalized for COVID-19 are vaccinated. For example, we can see from data from the the Israeli government data dashboard that nearly 60% of all patients currently hospitalized for COVID-19 (as of August 15, 2021) are vaccinated (downloaded data set and details are found at the bottom of this post). Out of 515 patients currently hospitalized with severe cases in Israel, 301 (58.4%) of these cases were fully vaccinated, meaning two doses of the Pfizer vaccine.
From this type of result in various places, I have seen tweets suggesting vaccines don't work or have lost their efficacy vs. severe disease, and I have seen other articles quote this type of figure as further evidence for the reduction of effectiveness of the vaccines in trying to justify 3rd shot boosters.
However, while these numbers are true, to quote them as evidence for low vaccine efficacy is wrong and misleading. Sometimes, with observational data there is confounding of multiple factors that can make it easy to misinterpret simple percentages like this, and the current vaccination situation in Israel brings a perfect storm of confounding factors that lead to confusion if not thought through carefully.
In particular, the key factors here that contribute to this confusion are:
1) High vaccination rates in the country (nearly 80% of all residents >12yr)
2) Age disparity in vaccinations, including
3) Nearly all older people being vaccinated (>90% of residents >50yr) and
4) The vast majority of unvaccinated being younger people (>85% of unvaccinated <50yr)
5) Older people are orders of magnitude more likely to be hospitalized with a respiratory virus than young people (residents >50yr are >20x more likely to have hospitalized serious infections than residents <50yr, and residents 90+ are >1600x more likely to have hospitalized serious infections than residents 12-15yr)
After accounting for the vaccination rates and stratifying by age groups, from these same data we can see that the vaccines retain high efficacy (85-95%) vs. severe disease, showing that when it comes to preventing severe disease, the Pfizer vaccine is still performing very well vs. Delta, even in Israel from whence the most concerning data have arisen.
( Much more at link. Charts too! )
He step-by-step walks through the data and provides links for such. Quite worthwhile to give it a skim.
The key point is to stratify data by age, otherwise one can fall to something called "Simpson's paradox".
And before the "anti-covid-vaxxers" start the attack (
), note that this author has another web page:Overwhelming evidence now that previously infected have robust immune protection against reinfection
-- Michael
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