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COVID-19 Vaccine Effectiveness in the Age of Delta and What Else We Can Do

Steven Kornweiss, MD covid-19 Leave a Comment

The US enjoyed a much needed lull of Covid-19 cases during the early summer of 2021. After a year of worry, many finally felt free from the virus and its ill effects, myself included. But, once the delta variant infiltrated the US, it caused a significant spike in cases. News-people launched a fresh barrage of bulletins, and states-people the latest deluge of decrees.

Bad news came from Israel, where despite a 60% vaccination rate of the population (80% of those eligible > 12 year of age), there is also a wave of cases. As of two weeks ago, roughly 500 patients were hospitalized in a country with a population of only 9 million. The big news in the headlines was that, of those hospitalized, 60% are fully vaccinated.

At face value, that sounds terrible.

An article from The Daily Beast that landed in my inbox tonight put it this way, "Ultra-Vaxxed Israel’s Crisis Is a Dire Warning to America."

Due in-part to data demonstrating breakthrough infections from Israel, commentators in the US are spreading doubt about the ability of vaccines to prevent severe disease from Covid-19.

I turned to our CDC to see how we’re faring in this department.

The CDC is currently providing access to data on breakthrough cases only through April 2021, which does not include the more recent delta variant wave.

According to the CDC, Covid-19 vaccines are effective. Here is the CDC messaging on breakthrough infections as of August 29, 2021:

COVID-19 vaccines are effective

To date, no unexpected patterns have been identified in the case demographics or vaccine characteristics among people with reported vaccine breakthrough infections.

COVID-19 vaccines are effective. CDC recommends that everyone 12 years of age and older get a COVID-19 vaccine as soon as they can.

For those who are fully vaccinated and get infected (ie, “breakthrough infections”), there is a risk of transmission to others.

That is why, if you are vaccinated or unvaccinated and live in an area with substantial or high transmission of COVID-19, you will be better protected if you wear a mask when you are in indoor public places, even if you are fully vaccinated.

People who are immunocompromised may not be protected even if fully vaccinated and may be more likely to have a breakthrough infection. They should continue to take all precautions recommended for unvaccinated people, until advised otherwise by their healthcare provider.

I would like to be reassured by the CDC, but current data on breakthrough infections in the US is unavailable, so I am forced to rely on analyses of data from other countries and on my own clinical experience.

Given the circumstances, it’s no surprise that many people are anxious and believe that we’re in for a never-ending pandemic.

Fortunately, anxiety is a treatable condition.

“Anxiety, unlike real fear, is always caused by uncertainty. It is caused, ultimately, by predictions in which you have little confidence. When you predict that you will be fired from your job and you are certain the prediction is correct, you don’t have anxiety about being fired. You might have anxiety about the things you can’t predict with certainty, such as the ramifications of losing the job. Predictions in which you have high confidence free you to respond, adjust, feel sadness, accept, prepare, or to do whatever is needed. Accordingly, anxiety is reduced by improving your predictions, thus increasing your certainty. It’s worth doing, because the word anxiety, like worry, stems from a root that means “to choke,” and that is just what it does to us.”

— The Gift of Fear by Gavin de Becker

I’d like to take de Becker’s advice and draw our attention to a very revealing and encouraging analysis done on the Israeli data by a biostatistics PhD from the University of Pennsylvania.

According to the analysis done by Dr. Morris, while it’s true that 60% of hospitalized patients in Israel are immunized, vaccine efficacy against severe disease remains high. He calculates that in Israel, vaccines are efficacious at preventing severe disease to the level of 91.8% in patients under the age of 50, and 85.2% in patients greater than 50.

How is this possible?

What follows is my summary of Dr. Morris’s analysis.

Most patients in Israel are vaccinated – some sources indicate 80% of eligible individuals over age 12, which comes out to roughly 60% of the total population. But, breakthrough infections are inevitable, especially in the infirm, immunocompromised, and the elderly. This group is always more likely to become ill, and now, they’re also more likely to be vaccinated. So, the most likely candidate for hospitalization is an elderly or infirm individual who is vaccinated. Ideally, vaccines would prevent hospitalizations even in this vulnerable population. But, we know this is not and has never been the case for any treatment. No matter how effective the treatment or prevention, some people will still succumb to the disease.

Here is Dr. Morris’s math:

Out of 1.3 million people who are not vaccinated, there are 214 severe cases.

Out of 5.6 million people that are vaccinated, there are 301 severe cases.

Here it is in tabular form:

Vaccination Status # of Severe Cases Total # of People Case Rate per 100,000
Yes 214 1.3 million 214/1.3 million * 100,000 = 16.4
No 301 5.6 million 301/5.6 million * 100,000 = 5.3

If we calculate a ratio, we find that the rate of severe cases is:

16.4/5.3 = 3 times higher in the unvaccinated than it is in the vaccinated

When these cases are stratified by age under 50 and age over 50, the numbers look like this:

Age Vaccination Status # of Severe Cases Total # of People Case Rate per 100,000
<50 No 43 1.1 million 3.9
<50 Yes 11 3.5 million 0.3
>50 No 171 186,000 91.9
>50 Yes 290 2.1 million 13.6

Severe cases are 3.9/0.3 = 13 times more common in unvaccinated patients under age 50.

Severe cases are 91.9/13.6 = 6.8 times more common in unvaccinated patients over age 50.

It’s worth looking at the raw numbers in the table above.

First, you’ll notice that the vast majority of the cases are, in fact, in patients over the age of 50.

Second, you’ll notice that there are only 11 severe cases in vaccinated patients under the age of 50, while there are 43 in unvaccinated patients under the age of 50.

It is important to keep in mind, these are just numbers from a single point in time. They do not reflect risk over time, just risk at the particular time when Dr. Morris analyzed the data, which happens to be in August of 2021. Risk calculations could change in the future if conditions change. But, for now, the data appear very favorable for the vaccinated.

The bottom line is this, these data can be presented in many different ways. If you look at the percent of hospitalized Covid-19 patients who are vaccinated, you see 60%. This looks bad. But, when you break down the actual numbers and cases per 100,000, it’s quite easy to see that being in the vaccinated group is quite preferable, and that vaccines still appear to be highly efficacious, even in Israel where many people were vaccinated five months ago, and even against the delta variant.

In conclusion, even based on the data from Israel, it is clear that vaccines are working — they are very effective at preventing severe Covid-19.

What else can be done?

Many people have noticed a media fixation on vaccines and masks to the exclusion of other measures. Isn’t there anything else that can be done?

I think the answer is Yes.

Observational data and clinical experience indicates that obesity and associated diseases account for an overwhelming majority of severe disease and death in young patients.

Patients under 50-60 years old who are requiring hospitalization or mechanical ventilation for Covid-19 disproportionately have a condition known as metabolic syndrome or some of its components (source).

A doctor can diagnose a patient with metabolic syndrome if the patient possesses at least three of the following risk factors.

Risk Factor Defining Level
Abdominal Obesity, by waist circumference > 40 inches for men, > 35 inches for women
Triglycerides > 150 mg/dl
HDL Cholesterol < 40 mg/dl for Men, < 50 for women
Blood Pressure >= 130 / >= 85
Fasting Glucose >= 110 mg/dL


A plethora of studies have been published linking obesity and related conditions to severe Covid-19 outcomes, but I think even the best studies underestimate the significance of this association. Nevertheless, this retrospective cohort study of 210 Covid-19 patients under the age of 45 found the following:


This is consistent with what my colleagues and I have experienced in the hospital. Younger patients who require hospitalization, ventilation, or who die from Covid-19 are much more likely to have obesity and related diseases than healthier people in the same age group.

While there’s been plenty of research on the topic, and the association has been noted by every clinician that I know, the message seems to be getting lost in these other debates about vaccination and masking.

It’s hard to become and remain physically fit. It takes time. It takes constant effort for most people, myself included, to maintain excellent nutrition and training (though it gets much easier over time). It takes viewing yourself as a fundamentally fit and healthy person in the long-term. We can take inspiration from Jeff Bezos’s space company, Blue Origin. Their motto is “Gradatim Ferociter,” which is latin for “step by step ferociously.” Step by step, we can become and stay fit and healthy by training, eating properly, managing our stress, and sleeping soundly.


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