Model vaccination
Prevent infection
Vaccine prevents the pathogen from establishing an infection in the body. A vaccinated person is less likely to get infected.
Prevent infection
Assuming a perfect vaccine against infection, the model can be designed as follows:
Vaccinated people \(V\) remain uninfected in their lifetime and do not participate in disease transmission.
Prevent infection
You can simplify this model by moving susceptible people to the \(R\) compartment because they also do not participate in disease transmission.
Prevent severe disease
A vaccinated individual still get infected but experiences a much milder form of the disease.
Prevent severe disease
Assuming a perfect vaccine against severe disease, the model can be designed as follows:
Prevent transmission
A vaccinated person still get infected, still get sick, but they are less likely to spread the disease to others.
Prevent transmission
Assuming a perfect vaccine against transmission, the model can be designed as follows:
\(I\) being the only source of infection that contributes to the force of infection. Vaccinated people \(S_v\) still get infected and become \(I_v\), but they do not transmit the disease.
All-or-nothing model
All-or-nothing (AoN, also called the polarized (Park et al. 2023), or take) model assumes that among vaccinated individuals, a proportion \(VE_P\) are completely protected, while the remaining fraction \(1 - VE_P\) remains completely unprotected (Zachreson et al. 2023; Park et al. 2023).
An effectiveness of 80% here implies that among vaccinated people, 80% are completely protected, and 20% receive no protection (World Health Organization 2013).
All-or-nothing model
Figure 1: All-or-nothing vaccination model (Park et al. 2023)
Leaky model
Leaky (or degree) model assumes that all vaccinated individuals are partially protected (Zachreson et al. 2023).
An effectiveness of 80% here implies that all vaccinated people have the endpoint of interest reduced by 80% compared to non-vaccinees.
Leaky model
Figure 2: Leaky vaccination model (Park et al. 2023)
Mixed effects
Imperfect vaccines often have a combination of effects: they can protect against infection, severe disease, and transmission at the same time.
Mixed effects
Assuming a vaccine with leaky effectiveness \(VE_L\) against infection and severe disease, the model can be designed as follows:
Multiple doses
Some vaccines require multiple doses. Below is the DynaMICE model (Verguet et al. 2015) for the 2-dose measles vaccine, assuming AoN effectiveness for both doses.
References
