The Effects of Vaccination Against COVID-19 Incidence: Is the current age-priorities appropriate?

. Age is an independent risk factor for COVID-19. Thus, the government of Indonesia prioritizes the elderly and adults with significant comorbidities for COVID-19 vaccination. To discover whether this policy is still appropriate, we evaluated the effects of vaccination against the COVID-19 incidence and infection risk.It was a retrospective cohort study of the NAR COVID-19 and Dashboard KPCPEN COVID-19 of the Depok City Health Department. The tests used to analyze the data were the chi-square and logistic regression tests. We discovered that there was a 92.7% total reduction in the COVID-19 infection rate with vaccination. The infection risk for COVID-19 in vaccinated people aged ≥ 60 years was far lower than those who were unvaccinated (RR = 0.10 vs. 1.72). In conclusion, vaccination reduces the transmission of COVID-19 significantly, especially in the ≥ 60 years age group. It affirms that the age priority policy in the vaccination policy is still applicable and does not require any amendments.


INTRODUCTION
The speed of the spread of COVID-19 infection has encouraged many governments worldwide to apply the various prevention methods recommended by the World Health Organization (WHO).The Severe Acute Respiratory Syndrome-Coronavirus-2 is an airborne virus transmitted through contact and droplets through coughing or sneezing that enter the body through the eyes, nose, or mouth.(1) Coronavirus Disease 2019 (COVID-19) droplets can travel as far as 1.8 m and survive up to two days.To control the spread of the disease and prevent more infections, various measures to prevent direct contact with the viral-loaded droplets have been recommended, with avoiding touching one's mouth, nose, and eyes being the most effective.Other measures include avoiding close contact with infected people, self-insolation when infected, disinfecting surfaces, using the proper coughing or sneezing practices, using masks and face shields in crowded places, social distancing, regular handwashing with soap and water or hand sanitizers, and the use of vaccination.(1) Vaccination reduces the incidence rate by training the immune system to fight the virus that causes a disease.When a vaccine enters the body, the immune system recognizes the invading germ, activating the cells that produce antibodies that fight the virus.The immune system also remembers the germ and how to fight it, so whenever it meets the same germ, it can destroy it before it causes a disease.(4)In addition, mass vaccination was found to be cost-effective or cost-saving regardless of vaccine type.(5) In Indonesia, COVID-19 the mass COVID-19 vaccination is regulated in Presidential Regulation no.99/2020 on vaccine procurement and vaccination implementation as countermeasures for the COVID-19 pandemic.(8) This regulation was then elucidated in the Minister of Health Regulation (PMK) no.84/2020 on implementing vaccinations as a countermeasure for the COVID-19 pandemic.(9) The regulation was then amended in PMK No. 10/2021.The goal of the vaccination is to reduce the transmission of COVID-19, lower the COVID-19 incidence rate and mortality rate, establish herdimmunity, and protect the people from COVID-19 to maintain productivity, both socially and economically.(9) According to the WHO, at least 70% of a country's population is recommended to be fully vaccinated, with 100% of health workers and 100% of its vulnerable population.(11) There are three priority groups for vaccination: high, medium, and low priority groups.Those that are included in the high-priority group for vaccination are older adults, younger adults with significant comorbidities (e.g., diabetes and heart disease) or severe obesity, people with immunocompromising conditions (e.g., transplant recipients, people with immunosuppressant therapy, cancer patients, children aged six months and older), pregnant women, and frontline health workers.This group is recommended to receive primary vaccination and booster doses 6 or 12 months after the last dose, depending on age and their health condition.(12) As vaccine supplies during the first year was inadequate, the high-risk and the elderly were more cost-effective.(5)Aside from health workers and public officers, the elderly and adults with significant comorbidities are among the prioritized population.(9) While those in the medium priority group are healthy younger adults without comorbidities under 50 to 60 years old and children and adolescents with severe obesity or comorbidities, it is recommended to receive the primary series and the first booster dose for this group.Moreover, the low-priority groups are healthy children and adolescents aged six months to 17 years.The vaccination for this group depends on vaccine availability, disease burden, cost-effectiveness, and other health priorities.(12) To evaluate whether a vaccine policy is appropriate or will need amendments, a framework is required to review vaccine effectiveness studies systemically.One of the frameworks used is the standard Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) that considers the quality of evidence on vaccine effectiveness against patient-important outcomes.Those outcomes are hospitalization for COVID-19 or medical visits caused by COVID-19, death due to COVID-19, post-COVID conditions and multisystem inflammatory syndrome (MIS), and symptomatic SARS-CoV-2 infection.(13) As such, we endeavour to evaluate whether the vaccine policy for age in Indonesia is appropriate by evaluating the incidence rate and mortality rate in each age group.
As one of the cities located near the Capital of Indonesia (Jakarta), Depok City has one of the highest disease burdens, and therefore became a priority location.We aim to discover the extent of the protection that COVID-19 vaccination provides in the real world and how accurate is the prioritization policy after it is applied in the real world.

METHOD
This was a retrospective cohort research that used the data from the New All Record (NAR) COVID-  1).In table 2, we can see that age influences the COVID-19 incidence and infection risk.The older an individual is, the higher the incidence and risk.According to (16), aging is complemented by the increase in the incidence and the severity of the disease.In their research, they found that the oldest age group was 3.28 times higher than the youngest group.While we found that the incidence and risk of contracting COVID-19 in the oldest group was 1.72 times higher in the oldest group than the youngest.This is possibly because of the process of immunosenescence, where the immune system experiences fundamental changes, particularly in the thymus and thus reducing the immune response.(17,18) This meant that the older age group required more protection from infection.

Research population characteristics
However, gender does not influence the COVID-19 incidence rate, nor does it influence the COVID-19 infection risk (see table 2).According to previous studies ( 19), ( 20),( 21), men had the same susceptibility to COVID-19.Therefore, sex does not play a role.

COVID-19 infection risk and vaccination
Table 3. COVID-19 incidence rate and infection risk based on vaccination status.
In table 3 we can see that the incidence rate and risk of contracting a COVID-19 infection is much lower in the vaccinated group compared to the unvaccinated group (RR=0.073;95% CI, 0.072-0.074;p=0,000).Which means that the infection risk for the vaccinated group was 92,7% lower than in the unvaccinated group.From our data, we discovered that COVID-19 vaccination in Depok City was more effective than compared to what (14) found or what(15) found.(14) found that the risk reduction of COVID-19 vaccination against COVID-19 infection was only 30% (in comparison to the unvaccinated group).(15) also found that COVID-19 vaccination reduces the infection risk, albeit also to a lower degree, 50% by the 14th day post vaccination and 64% by the 21st day.Since COVID-19 vaccination does reduces the infection rate and risk, then the policy for mass vaccination to prevent COVID-19 infection was correct.14), (15), where vaccination reduces the risk for COVID-19 infection significantly in all age groups.However, since older individuals are more prone to more severe disease and the age group with the highest incidence rate and risk of COVID-19 infection is the ≥ 60 years population, the need is more urgent for the elderly.Therefore, the policy to prioritize the elderly and older adults is appropriate.Although men and women have the same susceptibility to COVID-19 infection (22), we discovered that vaccination in men was more successful in reducing the COVID-19 incidence and infection risk.Table 5 shows a 1% difference in the incidence rate and a 0.01 difference in the infection risk.It is similar to what previous studies have found, where after vaccination, men were less susceptible than women.(23) Since the mortality rate in men was found to be higher than in women, preventing the infection at the beginning is important.(22) As we analyzed the data, we discovered several limitations in this study.There was limited data on the age or date of birth in one of the databases used, only age groups were available.We also could not access data on the uninfected and unvaccinated population of Depok City.

CONCLUSION
In conclusion, this study discovered that age highly influences the incidence and risk of infection of COVID-19.The older an individual, the more likely they are to be infected.Especially since the rates are higher in the elderly group, the lack of immune response or immunosenescence in the elderly population will also influence this.Therefore, for the elderly, vaccination is more urgent, and prioritization based on age is necessary and correct.Men also need more protection than women, though not as much as the elderly do.Please note that vaccine effectiveness will wane.Therefore, boosters might be necessary.Several studies on boosters have stated that boosters still reduce the incidence, hospitalization rate, disease severity, and mortality rate (24,25).However, more consideration and research are necessary since such an endeavor's cost and vaccine availability would pose an issue.(5)

RECOMMENDATIONS
Based on the results of this research, we recommend that the government maintain the agepriority policies for COVID-19 vaccinations and apply them to any future epidemics/pandemics.However, more research is necessary to determine whether vaccine boosters are necessary, at which vaccination dose it is the most effective, and its impact on mortality.
19 data base and the Komite Penanganan COVID-19 dan Pemulihan Ekonomi Nasional (KPCPEN) COVID-19 Dashboard of the Depok City Health Department to access the vaccination status and COVID-19 infection status of citizens of Depok City from January 14, 2021 to Januari 13, 2023.The research ethics approval was obtained from the Research Ethics Committee of the Faculty of Public Health of the University of Indonesia, with

Table 1 .
Characteristics of the study population in each age group.Registered in Depok City's NAR COVID-19 Database  Registered in Depok City's KPCPEN dashboard  Confirmed COVID-19 positive based on PCR and/or Rapid Antigen Testing  Have Depok City Identification Card In this study, more men were involved than women (53.36% vs. 46.64%).Based on age group, the group with the largest amount of participants was age 31-45 years (26.54%) and the least was age ≥ 60 years (10.97%).More people were vaccinated than not (92.48% vs. 7.52%), and most have received 2 vaccinations (69.25%).Of the 859.612 people involved in this research only 122.999 people were diagnosed as COVID-19 positive (14.31%), and out of that number, only 1.43% died.NAR COVID-19 Database from Depok City Health Department (n=160,214) KPCPEN Vaccination Dashboard for Depok City (n=2,352,085) Total=2,461,786 Inclusion criteria:  COVID-

19 infection risk in each age group and sexTable 2 .
COVID-19 incidence and infection risk in each age group.

Table 4 .
The effects of COVID-19 vaccination against the COVID-19 incidence rate and infection risk in each age group.

Table 4 ,
we can see that COVID-19 vaccination reduced the risk of contracting COVID-19 by a significant degree in each age group.All the unvaccinated people in this research were found to be COVID-19 positive (100%) in all age groups, while only 4.37%-9.66% of vaccinated people were found to be COVID-19 positive.It means that vaccination significantly reduces the rate and risk of contracting COVID-19 in all age groups, even when the incidence rate and risk of infection increases with age.Similar findings were found in studies of COVID-19 vaccines(

Table 5 .
COVID-19 infection rate and risks of each gender based on vaccination status.