We've all learned a lot about SARS-CoV-2 in the past 2 years. However, once again I'm reminded about how much we have to learn; the virus continues to surprise us. First, a bit about last week's ACIP meeting.
Number Needed to Vaccinate
I had hoped the ACIP would give a bit more specific advice for individuals to decide about a second booster dose. It seems clear that the potential benefit to those who are generally healthy and under 50 years of age is minimal and probably doesn't warrant widespread second boosting of those individuals. However, not everyone older than 50 has the same risk factors, and ACIP mostly took a pass in advising the public about how to think this through. I think they should have tried a little harder with that.
On the other hand I was very pleased that Dr. Sarah Oliver presented nice graphical information of the relative benefits of primary series and boosters. As you can see below, the biggest bang for the buck is the primary series plus first booster dose. Don't lose track of that. A second booster dose has some benefit, but the returns on that investment are smaller.
The number needed to vaccinate (NNV) basically states how many individuals would need to be vaccinated to prevent one additional adverse outcome of interest. While studies have shown this isn't too effective in communicating risks and benefits to the general public, I find it very useful to assess strategy. Here is Dr. Oliver's NNV calculation from the same presentation, using hospitalization as the outcome of interest:
So, a second booster isn't without benefit, but the incremental benefit is relatively small. From a public health perspective, what this is telling us is that we need to expend our largest efforts in vaccination of those who are unvaccinated or who have not received their first booster. Keep in mind that because our case monitoring is less precise now due to pandemic fatigue/apathy, these estimations are more prone to error. Also, SARS-CoV-2 is a moving target; numbers today may not apply in another week or 2. Which brings us to our next subject.
Another Sublineage Breaks Out of the Pack
The most astonishing development I saw this past week is the rapid increase of the new omicron sublineage BA.2.12.1. Look at how it seems to be taking over in the US:
Once again we will need to recalibrate all our numbers. Clearly BA.2.12.1 has a selective advantage, perhaps rising more quickly than did BA.2. We haven't seen an uptick in hospitalizations yet so maybe it doesn't have enhanced virulence, but it is at least more transmissible. I'm keeping my fingers crossed that BA.2.12.1 won't bring a large increase in severe disease.
In the meantime, I'm going to take a short break on this sunny Sunday in Silver Spring and enjoy a cup of coffee on the patio. Tomorrow is another day in COVIDland.