Vacunas contra la malaria: el problema de medir su eficacia sin considerar el cuándo y el dónde – Blog

Comparing vaccines with different trials can be misleading if the moment of vaccination and seasonal transmission of the disease is not considered.

Many infectious diseases can be prevented, totally or partially, through more than one vaccine in the market, so compare these options is a usual practice. However, making direct comparisons is expensive and a whole logíto retro. This leads to, often, the efficacy of vaccines are compared a start from different trials. But to what point are you real graves comparisons of these between essays? In an opinion article that we have Published Recientse in Lancet infectious diseases I argue that this focus can be misleading, specially when the transmission of the disease in question, as in the house of malaria, does not happen constantly throughout the year or in all the places in the same way.

A often compares the efficacy of vaccines a start from different trials. But to what point are you real graves comparisons of these between essays?

Comparison of the two vaccines approved against malaria

In recent years, the World Health Organization (WHO) has approved two malaria vaccines: RTS, S/AS01E AND R21/Matrix-M. Both are aimed at the same protein of malaria parasite, but are formulated in a different light. Both have gone through phase 3 tests on a large scale in Álica and have shown promising results:
• Rts, s: 55% efficacy in the first year
• R21: 72% efficacy in the first year

So, is R21 clarify the best vaccine for more than 15% efficiency? Not necessarily.
Of course, these estimates of vaccine efficacy come with confidence intervals, but what is often overlooked is that they are added for a time: basicamme, their effect is averaged for a whole year or time lasts eliguelo. But here is the detail: Malaria does not impact evenly throughout the yearBut it does so in mayor measured during the rainy stations, when the mosquitoes are everywhere. And, in parallel, the protection of the vaccine does not remain constant, but decreases over time.

The problem of using averages to measure the effectiveness of vaccines

Imagine that you want to evaluate the effectiveness of a waterproof jacket seeing how much you get wet for a year. Now, suppose and impiebe begins to deteriorate when you have been using it for a few months. If you start the test in July, just at the beginning of the rainy season, the impermable will be new when you need it most. But if the test begins in January, during the dry season, by the time the rains arrive the waterproof could already be full of holes. Although the waterproof is the same, the results of the evaluation of an annual evaluation would be very different. Malaria vaccines work similarly: their protection decreases over time, so the fact that they remain effective at the beginning of the malaria season to influence significant in its total efficiency. And that difference does not have to be seen with the vaccine itself, the breast with the moment in which the vaccine was administered during the test.

What our Effective Business Analysis found, Sy R21

We examine the data of the RTS, SY R21 tests and perform simulations to see what would happen if the vaccinations had been carried out at different times of uneasiness.
This is what we find:
• In Africa regions that participated in the clinical trial with grana seasonality such as Burkina Faso, the efficacy of RTS, S could vary Up to 20 percentage points Sports of the month of vaccination: from 46% to 66%.
• For R21, PLACES WITH SEACATIONAL MALARY Reported greater efficacy (75%) than those where malaria is not seasonal (67%), main because vaccination vaccination was better synchronized with malaria peaks.

So the apparent superiority of R21 in some cases should not be necessary to better biology, but partly a union Better moment of vaccination.

The apparent superiority of R21 in some cases should not be necessary to better biology, but partly at a better time of vaccination

Why the key key consider the time in the effectiveness of vaccines

These findings have important implications for the way:

• We compare vaccines evaluated in different clinical trials
• We compare the effectiveness of the same vaccine between different population subgroups within the same trialEither between different geographical regions or depending on the time people were vaccinated, for example, before or after an outbreak or the high transmission season
• We critically interpret those resulting from clinical trials

If we do not take into account the intensity and how the transmission of cooling varies during the period of monitoring of the trials, we run the risk of underestimating the effectiveness of a good vaccine, or of overestimating that of one that simplifies

Towards a better stratification of evaluation and application of vaccines

We propose some simple solutions:
• Estimates of using efficacy of the species vaccine according to time, instead of based on annual averages or on prolonged periods.
• Highlight intensity and variations in transmissionWhich can be obtained easy for the data of the control groups in the trials.
• Plan the administration Of vaccines according to the parking lots, I specially, when their efficiency decreases rapidly.

These ideas are not limited to malaria: also a relevant son for many tibras other vaccines, from the flu of the Covid-19, where I eliminate vaccination and the decrease in immunity with the pure time of time son of the key.

The next time you see a vaccine promoted as «60% effective», ask yourself not only for the type of vaccine and vaccinated population but also: effective when and where?

Conclusion

In the case of many infectious cooling, the results of vaccine tests do not depend only on the level of protection that are right, the sinus also on the intensity of the transmission of cooling and cresses varies to link time. When paying more attention to how they interact the deminution of vaccine immunity and transmission of the disease, we can make fairer comparisons and ensure that vaccines are used when more benefits can provide. So the next time you see a vaccine promoted as «60% effective», ask yourself not only for the type of vaccine and vaccinated population but also: Effective when and where? That question could be more important than we were.

Reference

Macià, D., Pons-Salort, M., Moncunill, G. and Dobaedo, C. (2025). The effect of the transmission of the disease on the efficacy estimates of the aggregate treatment in time: a critical analysis of the factors that influence phase 3 tests of the Malaria Vaccine RTS, S and R21. Lancet infectious diseases. https://doi.org/10.1016/S1473-3099(25)00090-8