Vaccination (pharmaceutical intervention)

```
pi_add_vaccine(
model,
preval,
susceptibility_reduction,
transmission_reduction,
recovery_enhancer,
death_reduction
)
```

- model
epiworldR model.

- preval
Initial prevalence of the vaccine.

- susceptibility_reduction
Reduction in susceptibility probability due to vaccine.

- transmission_reduction
Reduction in transmission probability due to vaccine.

- recovery_enhancer
Probability increase in recovery due to vaccine.

- death_reduction
Reduction in death probability due to vaccine.

Returns an object of class epiworld_model, where model is substituted with the model name.

Other interventions:
`interventions_add_all()`

,
`npi_add_masking()`

,
`npi_add_school_closure()`

```
library(epiworldR) # for ModelSEIRCONN function
model <- ModelSEIRCONN("COVID-19", n = 1000, prevalence = 0.05,
contact_rate = 4, transmission_rate = 0.1,
incubation_days = 7, recovery_rate = 0.14)
run(model, ndays = 100, seed = 123)
#> _________________________________________________________________________
#> Running the model...
#> ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| done.
#> done.
pi_add_vaccine(model, preval = .8, susceptibility_reduction = .9,
transmission_reduction = .5, recovery_enhancer = .5,
death_reduction = .9)
```