Prediction of effectiveness of universal rotavirus vaccination in Southwestern Vietnam based on a dynamic mathematical model

Vaccinating young children against rotavirus (RV) is a promising preventive strategy against rotavirus gastroenteritis (RVGE). We evaluated the relative risk reduction of RVGE induced by universal vaccination in Vietnam through dynamic model analysis. We developed an age-stratified dynamic Vaccinated-Susceptible-Infectious-Recovered-Susceptible model to analyze RV transmission and assess vaccine effectiveness (VE). We assumed 3 different vaccine efficacies: 55%, 70%, and 85%. For model calibration, we used a database of patients under 5 years of age admitted to Ho Chi Minh No.1 Hospital with RVGE between January 2013 and December 2018. Assuming a vaccination rate of 95%, the number of RVGE hospitalizations after 5 years from universal RV vaccination decreased from 92,502 cases to 45,626 with 85% efficacy, to 54,576 cases with 70% efficacy, and to 63,209 cases with 55% efficacy. Additionally, RVGE hospitalizations after 10 years decreased from 177,950 to 89,517 with 85% efficacy and to 121,832 cases with 55% efficacy. The relative risk reductions of RVGE after 10 years were 49.7% with 85% efficacy, 40.6% with 70% efficacy, and 31.5% with 55% efficacy. The VE was 1.10 times (95% CI, 1.01–1.22) higher in the 4-months to 1-year-old age group than in the other age groups (P = 0.038), when applying 85% efficacy with 95% coverage. In conclusion, despite its relatively lower efficacy compared to high-income countries, RV vaccination remains an effective intervention in Southwestern Vietnam. In particular, implementing universal RV vaccination with higher coverage would result in a decrease in RVGE hospitalizations among Vietnamese children under 5 years of age.


Appendix
The first age group labeled as "0m-4m" represents individuals aged equal to or above 0 months but below 4 months, and the same principle applies to the other groups.The final group signifies individuals aged 5 years and above.

Figure S3
. Prediction of the age-specific incidence rates of rotavirus gastroenteritis hospitalizations from 2019 to 2032.The first age group labeled as "0m-4m" represents individuals aged equal to or above 0 months but below 4 months, and the same principle applies to the other groups.The final group signifies individuals aged 5 years and above.The solid lines show the average incidence rate for each age group with the estimated parameters.
The shades, on the other hand, depict the range between minimum and maximum incidence from the profile-likelihood-based confidence ranges of parameters.Text S1.Mathematical model details to describe Vietnamese rotavirus dynamics.
We constructed a differential equations system to describe the dynamics of rotavirus in response to vaccines in Vietnam.The detailed differential equations are shown below.Given that some ages are 0 years old, the indices for the force of infection  and the aging  start from 0 and are represented as subindex.For each year, the number of births is  year and the total number of deaths is the same.First, we wrote the dynamics for the youngest people aged from 0 to 4 months as follows.
The people aged from 4 months to a year are vaccinated when they are aged from the previous compartment.Therefore, the aging processes for the vaccinated and susceptible groups are slightly different than the others.
For the older age classes, the vaccinated and susceptible people have the following dynamics instead.

{ 𝑑𝑉
The infection dynamics is described as follows: We assumed that the oldest people have mild symptoms as described above.We assumed that the number of people is stable for a year, implying that death rates in people over 5 years old are equal with birth rates in people aged less than 4 months.Every September, the model adjusts population proportion with the demographic data.

Figure S1 .
Figure S1.Population dynamics (left axis) for young children under 5 years old and (right axis) for the people equal to or 5 years old.

Figure S2 .
Figure S2.Parameter estimation results: the dots represent the number of monthly hospitalizations per 10,000 capita and the line plots the expected number of hospitalized people predicted by the model with a shaded region owing to the 95% confidence interval.

Figure S4 .
Figure S4.Age-specific RVGE incidence rate under 5 years old.The first age group labeled as "0m-4m" represents individuals aged equal to or above 0 months but below 4 months, and the same principle applies to the other groups.The final group signifies individuals aged 5 years and above.

Figure S5 .
Figure S5.Prediction of the age-specific incidence rates of rotavirus gastroenteritis hospitalizations from 2019 to 2032 with the hospitalization rate from (A) Ho Chi Minh City and (B) Dong Thap Province.The first age group labeled as "0m-4m" represents individuals aged equal to or above 0 months but below 4 months, and the same principle applies to the other groups.The final group signifies individuals aged 5 years and above.The dashed lines show the average incidence rate for each age group with the estimated parameters.The shades, on the other hand, depict the range between minimum and maximum incidence from the profile-likelihood-based confidence ranges of parameters.

Figure S1 .
Figure S1.Population dynamics (left axis) for young children under 5 years old and (right axis) for the people equal to or 5 years old.

Figure S2 .
Figure S2.Parameter estimation results: the dots represent the number of monthly hospitalizations per 10,000 capita and the line plots the expected number of hospitalized people predicted by the model with a shaded region owing to the 95% confidence interval.The first age group labeled as "0m-4m" represents individuals aged equal to or above 0 months but below 4 months, and the same principle applies to the other groups.The final group signifies individuals aged 5 years and above.

Figure S3 .
Figure S3.Prediction of the age-specific incidence rates of rotavirus gastroenteritis hospitalizations from 2019 to 2032.The first age group labeled as "0m-4m" represents individuals aged equal to or above 0 months but below 4 months, and the same principle applies to the other groups.The final group signifies individuals aged 5 years and above.The dashed lines show the average incidence rate for each age group with the estimated parameters.The shades, on the other hand, depict the range between minimum and maximum incidence from the profile-likelihood-based confidence ranges of parameters.

Figure S4 .
Figure S4.Age-specific RVGE incidence rate under 5 years old.The first age group labeled as "0m-4m" represents individuals aged equal to or above 0 months but below 4 months, and the same principle applies to the other groups.The final group signifies individuals aged 5 years and above.

Figure S5 .
Figure S5.Prediction of the age-specific incidence rates of rotavirus gastroenteritis hospitalizations from 2019 to 2032 with the hospitalization rate from (A) Ho Chi Minh City and (B) Dong Thap Province.The first age group labeled as "0m-4m" represents individuals aged equal to or above 0 months but below 4 months, and the same principle applies to the other groups.The final group signifies individuals aged 5 years and above.The dashed linesshow the average incidence rate for each age group with the estimated parameters.The shades, on the other hand, depict the range between minimum and maximum incidence from the profile-likelihood-based confidence ranges of parameters.