How long until the next booster shot against Covid-19? The answer depends on the vaccine, the variant, as well as the health status of the patient. For a healthy individual, the immune protection provided by an mRNA booster vaccine (Pfizer/BioNTech, Moderna) will last more than a year, concludes a US study based on mathematical modeling of the effects of the vaccine. On the other hand, for patients at increased risk due to cancer or weakened immunity, revaccination should be carried out much more frequently.
Mathematical model of the impact of the virus on the immune system
“It is still unclear how long booster doses confer immunity, how effective they are against emerging variants, or how to tailor vaccination schedules in high-risk populations,” the researchers summarize in their study, published in the journal PNAS. To see more clearly, the team decided to model the effects of vaccines according to the options and condition of patients receiving boosters using a “mechanistic” mathematical model.
How long until the next booster shot against Covid-19? The answer depends on the vaccine, the variant, as well as the health status of the patient. For a healthy individual, the immune protection provided by an mRNA booster vaccine (Pfizer/BioNTech, Moderna) will last more than a year, concludes a US study based on mathematical modeling of the effects of the vaccine. On the other hand, patients at increased risk due to cancer or weakened immune systems should be given booster doses much more frequently.
Mathematical model of the impact of the virus on the immune system
“It is still unclear how long booster doses confer immunity, how effective they are against emerging variants, or how to tailor vaccination schedules in high-risk populations,” the researchers summarize in their study, published in the journal PNAS. To see more clearly, the team decided to model the effects of vaccines according to the options and condition of patients receiving booster immunizations using a “mechanistic” mathematical model. So based on the known functioning of the virus and its spread during lung infection, innate and adaptive immune responses or thrombosis formation, these small clots increase the risk of death after Covid-19. A set of differential equations allows the model to describe the dynamics of these processes and test hypotheses about the interactions between viral infection and various components of the immune response to this infection. The model is then validated using real patient clinical data.
Over a year of protection in healthy people
“We used this model to simulate how differences between virus, patient, and vaccine characteristics can affect Covid-19 outcomes,” says Radiation Oncology Professor Rakesh K. Jain, who led these studies. The analysis includes the first options Alpha and Delta, as well as Omicron, most of today’s and even hypothetical future options. Result: for all of these options, adding a booster dose after the first two provides a healthy person with immune protection for more than a year. This does not mean 100% effective because, let’s remember, the protection provided by vaccines is not infallible at the individual level, and its main goal is to stop the spread of the disease at the population level.
Reminder every six months for fragile people
In debilitated patients, the model predicts a reduction in viral load and thrombus formation of more than 60% if the booster mRNA vaccine (Pfizer/BioNTech and Moderna) is given 6 months after the previous dose, rather than 3 months. In contrast, a second booster appears to provide the same protective effect between 3 and 6 months after the first boost for immunosuppressed patients. “Our results therefore indicate that the best interval between the first and second booster injection is 6 months for all vaccines” for these high-risk patients, the researchers conclude.
The researchers also point out that for the Johnson & Johnson vaccine, which is based on a viral vector rather than mRNA, and appears to be fading faster, “additional booster doses should be considered for all people,” both healthy and debilitated. .
Tailor booster rates to the patient
Specifically, the researchers then tested their model with most Omicron variants with a delay of 6 months between the first and second boosters. The model then gave the rate of virus degradation by antibodies for both at-risk patients and healthy and young people. “Our model predictions show that booster doses of new vaccines will benefit risk groups more than healthy people,” they conclude. “For people who are immunocompromised or cancer patients receiving immunosuppressive therapy (such as chemotherapy), the booster effect may disappear and may need to be considered more frequently.”
A mathematical model cannot fully predict the full biological complexity of different variants of the virus, different types of cancer, chemotherapy, interactions with the immune system, or patient profiles. However, as Covid-19 becomes endemic (recurring every year), this model suggests that rotating vaccine boosters according to risk profile would be beneficial in preventing new variants from developing and controlling resurgences.