During the past two years, the covid-19 pandemic affected almost all people in the world, and every aspect of people’s lives has been affected. The elderly, those were considered the most vulnerable population in society, showed a higher hospitalization and death rate compared with other age groups, thus several countries, including Brazil, initiated a national COVID-19 vaccination program with senior citizens.
To better understand how vaccines performed in preventing severity and deaths due to COVID-19, Brazil researchers developed a Bayesian statistical model to estimate the potential number of hospitalizations and deaths that prevented by vaccine campaign in 3 different time setting scenarios of vaccination rollouts, correspondent numbers were compared to a putative scenario with no vaccination.
This study represent the number of hospitalization and death of different age groups received vaccine at different time setting during 1st Jan. to 29th Aug. 2021.
Figure 1: Posterior distribution of hospitalizations (left) and deaths (right) due to COVID-19 potentially averted by vaccination between January 1, 2021, and August 29, 2021, by age group, with the realized (dark orange), 4 (light purple) and 8 weeks earlier (dark purple) vaccination roll-out. Check legend for grey scale.
Results showed that compared to a hypothetical scenario of the absence of vaccines, there are an estimated 167,000 hospitalizations and 77,000 deaths were avoided.
Since only the direct effect of vaccines was considered, this estimation didn’t calculate the herd immunity effect, the actual number of prevented hospitalization and death should be even higher.
If we evaluate another hypothetical scenario, considering an eight weeks earlier rolled out, Brazil could have saved a minimum of additional 48,000 lives and avoided another 100,000 hospitalizations compared to what happened (Table 1).
Table 1: Estimated reductions in hospitalizations/deaths by age group and vaccine roll-out. 60+ is the aggregate of all age groups of older adults.
It is worth noting that, Brazil started national vaccination against COVID-19 on 18 January 2021, and priority groups include the elderly. Most of the elderly population received CoronaVac®, suggesting that CoronaVac® has played an important role in preventing COVID-19 hospitalizations and deaths.
In a press conference held by the Joint Prevention and Control Mechanism of The State Council on February 26, 2022, experts emphasized that during the epidemic of omicron strain, the highest number of reported cases globally in a week was close to 24 million, four times the previous peak of the epidemic of other variants. Surveillance have found that omicron strain poses a very high risk of severe illness and death in the elderly. Data recently released by the Infectious Diseases Division of Hong Kong's Centre for Health Protection showed that the elderly accounted for the majority of early deaths, with a fatality rate of 0.03% for those who were vaccinated and 0.54% for those who were not, an 18-fold difference. The mortality rate for those over 80 years of age who had not completed vaccination was 4.34%, and the mortality rate for those who had not been vaccinated was higher.
Elderly people who have not been vaccinated or who have not received booster shots should complete the full vaccination or booster shots as soon as possible if they are eligible in accordance with relevant regulations.