Reacción a "The vaccine booster may be more effective if administered in the same arm"

The study has two clearly distinct parts: one conducted on mice, which would not be of practical interest until the data is confirmed in humans, and the other conducted on humans: 30 people, divided into two groups of 20 and 10, respectively, which seems like a small sample size to draw definitive conclusions (it may be useful for generating hypotheses). There is one part that seems clearly incorrect, which is when Figure 6H refers to ‘expected vaccine efficacy’: to date, it has not been possible to predict efficacy against COVID-19 based on antibody titres.

It provides new information on some immunological aspects, but this is of little practical application in the current context. There are some articles published on this subject, one of which supports the results of this study, while another says that the result would be similar when vaccinating the same limb as the opposite limb.

Another article published in The Journal of Clinical Investigation [which gave results contrary to the current one] is suggestive because the sample size is almost 1,000 people, which gives it significant statistical power. However, the diversity of results in different studies tells us that this is still an issue without sufficiently firm evidence and that more research is needed.

The difference between immune response and clinical protection must also be taken into account. Many results measured by immune response do not translate into greater or lesser clinical protection against the disease. In other words, in general, we always prefer a stronger immune response, a higher antibody titre, etc., but this does not necessarily translate into better clinical protection (for example, there are vaccines that have what we call a protective correlate: the antibody titre value at which we are considered to be protected. Well, theoretically, you always prefer a higher titre, but in practice, once the immune response, which we consider protective, has been achieved, having higher titres does not translate into greater clinical protection).

For all these reasons, the results must be put into perspective, because there is currently conflicting data between different studies and because, even if they were consistent, we would have to put that data into context with regard to whether or not there is greater clinical protection. Nevertheless, these are interesting data that will need to be investigated further.

[Regarding possible limitations] Perhaps the greatest limitation is the small sample size (30 people) and the short follow-up period, with other studies on this topic having a much longer follow-up period.