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Thursday, December 08, 2022

COVID-19: Who should get the fourth dose of the vaccine? A mathematical model can help decision making

COVID-19: Who should get the fourth dose of the vaccine?  A mathematical model can help decision making

Although more and more people have an immune shield against SARS-CoV-2, either because they have recovered from a previous infection, have been vaccinated, or both, the virus evolves with the appearance of new genetically distinct forms. continues to happen. These include high rates of transmission and decreased immune defenses against reinfection.

one round of bivalent reinforcement

In this context, the European Medicines Agency (EMA), the European Center for Disease Prevention and Control (ECDC) and other health agencies recommend a new round of vaccine boosters with a new configuration vaccine for this autumn-winter . In fact, on 26 September in Spain, people over the age of 80 have been called to administer it.

These new vaccines contain messenger RNA from the original version of the virus (Wuhan-Hu-1) and equal parts Omicron ba.1. Its goal is to increase its effectiveness against its predecessors, which focused only on the basic version.

As in previous occasions, vaccination is recommended based on the risk of infection or its severity, giving priority to the most vulnerable, such as the immunosuppressed and the elderly. Social-health workers will also be pricked in advance to avoid a possible collapse of the health system.

On the other hand, the safety and effectiveness of the new booster have not been directly tested in clinical trials to date. For the deployment of vaccines against SARS-CoV-2, a strategy of anticipation similar to that of influenza vaccines has been followed, which prevents knowing their true efficacy and safety through clinical trials.

The currently proposed program does not take into account immunological history to optimize boosting, leaving many to wonder whether, when and how their vaccination history and previous infection play a role. Can knowing the amount of antibodies we have can help make a decision? Because booster doses have costs, including materials and human resources.

To this should be added the side effects that advise responsible use of vaccines. In fact, health agencies themselves recommend not re-pricking a person until three months after their last infection or vaccination.

Antibody Question

Several research groups, including ours, have shown that people with hybrid immunity (those who have had a previous SARS-CoV-2 infection and have been vaccinated) experience fewer infections and have more active antibodies than people who have been vaccinated. has not been imposed. , It would be reasonable that individuals with this type of immunity did not follow the same general vaccination regimen, as the behavior of their memory immune cells protects them more effectively in the event of encountering the virus again.

On the other hand, in our study we have detected a great individual variability within both subgroups. In fact, some people who have only been vaccinated (without a previous infection) maintain a very high and constant level of antibodies over time, with hardly any decline; while in others they descend very quickly, so that they To be embroiled in a blow or accident, The identification of these subgroups will be of great interest to health officials and help them decide whether to receive a booster.

Our group has observed that it is possible to mathematically model, in a simple way, the antibody degradation curve (anti-RBD IgG) with just two blood tests. Thanks to these models, we can predict the moment these antibodies drop below a certain threshold. It also allows us to estimate how many we will have over a specific period of time (for example, within a year).

vaccinate only when necessary

Why is this discovery important? First, it is a useful tool for predicting antibody levels and thus evaluating what protection the vaccine can provide us and the risk of infection in order to plan the optimal time to receive a booster. . And second, it allows us to classify people based on their immune status and identify vulnerable groups of people.

Finally, an individualized vaccination booster schedule should be developed based on antibody levels and the risk of infection and its severity. Our modeling can also be used in a variety of circumstances, such as the emergence of new viral variants or the development of improved vaccines. This approach would therefore allow to rationalize the administration of booster doses of SARS-CoV-2 vaccines, apply them only when necessary, and avoid potential side effects.

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