Data continue to look encouraging in terms of case rates, hospital bed availability, and other pandemic tracking across the country, notably with exceptions and still at substantial transmission levels in many areas. Let's look today at some slightly conflicting reports of vaccine effectiveness (VE) and a bit of reflection 2 years after the start of all this.
Which Numbers are Correct?
The answer, of course, is that both are likely correct, within the imperfect data analyzed. Last Monday, February 28, the New York State Department of Health posted a pre-print (non-peer reviewed) study that showed low rates of VE in children 5-11 years of age compared to 12 years and older who received a higher dose of the Pfizer mRNA vaccine. I had questions about the accuracy of the data in the study, a problem with all studies like this one that uses administrative databases. If the authors can answer those questions satisfactorily when it is peer-reviewed, it did indicate that VE wanes faster in the children who received the lower dose.
Then on March 1 the CDC released their own data looking at the same question. It also is based on administrative datasets but has the advantage of being more established and more likely to be free of serious errors. Also, getting through the CDC review process is a bit more like peer-review, though most of the peers are CDC personnel which could introduce unintentional bias. I'll focus on the CDC numbers because I think they are more reliable. Here is the bottom line for VE against laboratory-confirmed COVID-19-associated emergency department (ED) and urgent care (UC) clinical encounters and hospitalizations (H). Note that time after vaccination varies because the younger age group was authorized for vaccine only recently. Also, some estimates have very wide confidence intervals (CI) because the number of events is too small to be more precise.
| Age Group/Vaccine Status | VE (95% CI) | |
| ED/UC* | 5-11 yo, 2 vaccine doses 14-67 days earlier | 51 (30 - 65) |
| 12-15 yo, 2 doses 14-149 days earlier | 45 (30 - 57) | |
| 12-15 yo, 2 doses > 150 days earlier | -2 (-35 - 95) | |
| H** | 5-11 yo, 2 doses 14-67 days earlier | 74 (-35 - 95) |
| 12-15 yo, 2 doses 14-149 days earlier | 92 (79 - 97) | |
| 12-15 yo, 2 doses > 150 days earlier | 73 (43 - 88) |
VE is similar relatively soon after receiving 2 doses of vaccine, suggesting less of an effect from the vaccine dose itself. Remember that 5-11 year-olds received 10 mcg doses compared to 30 mcg in the 12-15 age group. The numbers of events for these children receiving a third dose was too low to calculate anything, but in the 16-17 year-olds a third dose seemed to produce a terrific rise in VE. Undoubtedly we'll see more reports about this from other jurisdictions as we have more time elapsed to observe VE.
Learning Now to Prepare for the Future
I'll close with a quick plug for 2 opinion items I read in the last few days. First is journalist Joel Achenbach's article in the Sunday Washington Post Magazine about 10 lessons learned so far from the pandemic. I especially noted #7: pandemics end psychologically before they do biologically. How true. Let's not get too complacent yet.
Second is a piece released this week in the New England Journal of Medicine talking about the need to develop capabilities to produce a vaccine within 100 days of the start of a new pandemic. The authors note that it took 326 days from the SARS-CoV-2 genetic sequence release in January 2020 to the emergency use authorization of the first COVID-19 vaccine. I've said before that this speed approached miracle status, so proposing lowering that to 100 days will take a bit of work. Let's hope we don't repeat past behavior and lose our research momentum when this pandemic calms down.