COVID vaccines, transmission, death & public health policy:
The CDC recently published a study as part of its MMWR to assess how well the COVID-19 vaccines and boosters impacted case numbers, deaths, and incident rate ratios (IRR) during the pre-Delta time period, Delta emergence (June ’21), Delta dominance (July-Nov’21) and during the emergence of Omicron (Dec’21). What is IRR? An IRR is a comparison of incident (new case) rates between two groups. For example, if something happens 4/10 times in 1 group and happens 7/10 times in another group, the IRR is 4/10 over 7/10 or .6
The CDC report, which was released early, is difficult to read and not presented in an eye-friendly fashion, which is something I think the CDC should really, really work on, so it took me longer than usual to go through the report and pull out the important stats. Honestly it was so painful to read, I was just going to ditch it, but I know a lot of my readers have been asking for recent data concerning vaccination status, infection rate and hospitalizations. And for the record, this study only includes people who are unvaccinated, fully vaccinated and fully vaccinated and boosted. It excluded those who were partially vaccinated.
What does the IRR tell us:
In 2021, the average case age-standardized IRR among unvaccinated individuals compared to fully vaccinated individuals decreased from 13.9 pre-Delta to 8.7 when Delta first emerged and 5.1 when the Delta variant dominated and 3.1 in December. This decline indicates reduced vaccine effectiveness for getting infected: (93% to 89% to 80% to 68%.) The IRRs for deaths among unvaccinated people vs fully vaccinated people were mostly stable across all months. The vaccine effectiveness against death was 95% in April-May, 94% in June and 94% during July’21-Dec’21. Take home point: The IRR indicates that the vaccine effectiveness against transmission clearly declined with time, but its effectiveness against death held up.
Between October and November, unvaccinated people had 13.9 times the risk for infection and 53.2 times the risk of death compared to fully vaccinated and boosted people, and 4.0 times the risk for infection and 12.7 times the risk of death compared to fully vaccinated individuals who did not receive the booster. When Omicron emerged in December’21, the case IRR decreased to 4.9 for fully vaccinated and boosted individuals and 2.8 for fully vaccinated individuals who were not boosted, relative to October-November’21.
Notably, the highest impact of booster doses against both infection and death when compared to the fully vaccinated without a booster was seen in those ages 50-64 and those older than 65. In simple terms, this means that the booster dose made the greatest difference in terms of protection from both infection and death in the older age groups.
Adult cases & Death Numbers from 25 Jurisdictions between April- Dec’21 for Unvaccinated vs Vaccinated:
Cases reported: 6,812,040 cases in the Unvaccinated and 2,866,517 cases in the Fully Vaccinated
Deaths reported: 94,60 in the Unvaccinated and 22,567 in the Fully Vaccinated
Rates of adult cases & deaths from 25 Jurisdictions for fully vaccinated vs fully vaccinated plus booster vs unvaccinated:
Cases during Oct-Nov’21: 25/100,000 fully vaccinated plus booster; 87.7/100,000 fully vaccinated; 347.8/100,000 for the unvaccinated.
Deaths during Oct-Nov’21: .1/100,000 for fully vaccinated plus booster; .6/100,000 for fully vaccinated; and 7.8/100,000 for the unvaccinated
(Notice that the fully vaccinated were still very protected from death compared to the fully vaccinated and boosted.)
Cases during Dec’21: 148.6/100,000 fully vaccinated plus booster; 254.8 /100,000 fully vaccinated; 725.6/100,000 for the unvaccinated.
From this report, we can say that the vaccines remained significantly protective against death. Folks who got boosted had the best chance of not getting infected and not dying when the Delta variant dominated, and not getting infected when Omicron started to take over. This protective effect was most prominent among people over age 50. We can also say that the vaccines helped reduce transmission, but their effectiveness to do that significantly declined over a few months, and especially with the onset of Omicron. The primary series or type of vaccine someone had first did not significantly impact the effectiveness of the booster dose.
What Does this Mean for Public Health Policy? Here’s the interesting part…
Well, in general, the vaccines remain protective against death. As I mentioned in a previous blog I wrote a couple months ago, that seems to be a consistent data point that we can rely on. However, with the onset of new variants and the passage of only a few months, vaccine effectiveness clearly declined, especially against preventing transmission and infectivity. Folks who got boosted on top of being fully vaccinate, regardless of the brand/type of vaccine they used in their primary series, had the best chance at not dying. Boosting clearly helps the older age groups more than the younger age groups. While the vaccine decreased one’s risk of getting infected, the trend in IRRs shows us that its effectiveness to do that decreased significantly over a few months and with the onset of new variants, particularly Omicron. Therefore, from a public health policy perspective, we should ask ourselves a couple of questions that I don’t necessarily know the answers to:
- What is the threshold to mandate a vaccine? If the vaccine shows significantly reduced effectiveness at reducing transmission, is it still logical and ethical to mandate? Do the vaccine passports still make sense? It’s great that it continues to be preventive against death but is that enough for things like vaccine passports? For example, Israel’s Green Pass (vaccine passport) was reassessed by their government this week. Despite very high case numbers, they got rid of most of the vaccine passport requirements, my guess is because the passports were not making an impact on transmission. We should discuss this, because transmitting and infecting others still disrupts the normal functioning of businesses, schools, airlines, travel and everyday life, not to mention allows for the virus to continually have hosts to mutate in and possibly lead to new variants. Also…with the significant decline in ability to prevent infection and transmission, we cannot reach herd immunity so as to protect the most vulnerable in society, or those who cannot get vaccinated. (Immunocompromised etc.)
- It’s great that getting boosted was even more protective against death and getting infected. However, a question a lot of people have including myself, what will be the ultimate recommended booster schedule? We know some folks have gotten a 4th dose already. The original booster was recommended just 5-6 months after the primary series. Is it ethical or sound epidemiology to mandate boosters if the vaccine shows significant decline in ability to prevent transmission? And is it safe or do folks have anything to worry about with repeated boosters of mRNA shots only months apart? That’s a fair question, I think.
- This study collaborates with other studies in showing that boosters are most effective and preventive in older age groups. Should we start to tailor our public health response by age? Is it time to do that?
Those are questions to consider. I know I’ve been discussing them with some of the peers I work with and not everyone agrees on what the approach should be. There is a lot of uncertainty– such is the nature of a pandemic. While frustrating, there isn’t much we can do about all the unknowns except accept the pandemic for what it is: a new virus that we are constantly learning new things about.
If you missed it, you can read my summary on the CDC’s recent study on natural immunity vs vaccine-induced.
Also check out: It’s not a misinformation problem, it’s a trust problem.
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See you soon- Eeks