By Dr. Eeks
A recent CDC study looked at COVID-19 cases as related to COVID vaccination status and recovery from previous infection in the states of California and New York between the period of May’21-Nov-21.
Four cohorts of adults over the age of 18 were considered in the analysis:
- Unvaccinated with no previous COVID-19 diagnosis
- Vaccinated with no previous COVID-19 diagnosis
- Unvaccinated with a previous COVID-19 diagnosis
- Vaccinated with a previous COVID-19 diagnosis
What did the analysis show?
In both states and compared to the 3 other groups, the rate of new cases of COVID-19 was highest among unvaccinated people who did not have a previous COVID-19 infection. The vaccinated persons without a previous diagnosis of COVID-19 had a 19-9-fold lower case rate in California and an 18-4-fold lower case rate in New York compared to the unvaccinated persons with no prior infection. The unvaccinated persons with a previous infection had a 7.2-fold lower case rate in California and an 9.9-fold lower case rate in New York. The vaccinated persons with a previous COVID infection had a 9.6-fold lower case rate in California and an 8.5-fold lower case rate in New York. Hospitalizations in California followed a similar trend.
By the week of October 3rd, compared to COVID-19 case rates among unvaccinated people who did not have a previous infection of COVID-19, case rates amongst vaccinated persons without a previous COVID-19 diagnosis were 6.2-fold lower in California and 4.5-fold lower in New York. Interestingly, rates were significantly lower in unvaccinated persons with a previous COVID-19 infection (29-fold lower in California and 14.7-fold lower in New York), and in vaccinated persons with a previous COVID-19 diagnosis (32.5-fold lower in California and 19.8-fold lower in New York). Hospitalizations in California followed a similar trend.
You’ll notice from the statistics in the above paragraph that the protection from previous infection was higher after the Delta variant became predominant. This was a period when vaccinated folks experienced waning immunity from the vaccines and as we know, the vaccines weren’t as effective against the Delta variant as the original COVID strain for which the vaccines were targeted.
What about hospitalizations?
This study looked at hospitalization rate only in California, not New York.
The hospitalization rate was always highest among unvaccinated persons who did not recover from a COVID-19 infection.
During June 13-26, compared to the hospitalization rate among unvaccinated persons without a prior infection of COVID-19, the vaccinated persons’ rate was 27.7-fold lower; the unvaccinated people who recovered from a prior infection had a 6-fold lower rate, and vaccinated people with a prior infection had a 7.1-fold lower rate. This pattern, like case rate, shifted when Delta became the most dominant variant.
During October 3-16, compared to the hospitalization rate among unvaccinated persons without previous COVID-19 diagnosis, hospitalization rates were 19.8-fold lower among vaccinated persons with no previous infection; 55.3-fold lower among unvaccinated persons with a previous infection, and 57.5-fold lower for vaccinated persons with a previous COVID-19 diagnosis. That 55.3-fold reduction in hospitalizations for those who had recovered from COVID-19 is a powerful testament to naturally-acquired immunity. As I’ve covered in a previous blog post, the evidence has been trending in support of naturally-acquired immunity producing a lasting protective effect. As this study shows, it clearly protected against both cases and hospitalizations (even better than the vaccinated/unrecovered during the Delta period in this study). This study does not suggest that anyone should go out and get COVID, particularly if you are unvaccinated. The completely unvaccinated did the worse whether it came to case rate or hospitalizations. What this study does do is add to the growing evidence in support of naturally-acquired immunity being protective. That should be considered for future public-health policy decisions.
As I wrote in my previous blog post, I was frustrated with how the mainstream media and even some fact-checking sites were portraying the evidence for naturally-acquired immunity as some sort of antivax rallying cry and misinformation. That’s both unfortunate and unscientific. Naturally-acquired immunity is part of the “herd immunity” equation for getting us to a good spot in our battle against COVID-19. While I have seen some folks claim it is being used as an “excuse” to not get vaccinated or that it as an argument against vaccination…, well it never was supposed to be that. Sadly, many people have an agenda today and much like religion, lots of people manipulate or use science to fit their own narratives.
Did the study have limitations?
Yes, of course, ALL studies do. 😉
A few of them include that people who had an infection in the past and were never diagnosed were miscategorized. Self-tests weren’t included in this analysis. The study was conducted before the Omicron variant and may not apply as well to that. We’ve seen surging case rates due to Omicron, even in the vaccinated. (That’s one reason people are pushing boosters so much, and naturally-acquired immunity may not hold up as well against Omicron.)
You can read the full CDC report here, but man, they make it really hard to read.
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