SARS-CoV-2 vaccines used in Chile remain highly effective in preventing hospitalization, ICU admission and death

Chile’s Health Ministry has provided the results of the “Effectiveness of the SARS-CoV-2 Vaccination Program” study. The investigation has updated the evaluation of the CoronaVac and Pfizer-BioNTech vaccines, while the AstraZeneca vaccine was assessed for the first time. The objective of this monthly report is to provide preliminary estimates on the effectiveness of the vaccines used in the National SARS-CoV-2 Immunization Plan. The analysis compares different results among a group of people who have and have not been vaccinated, taking into account variable such as age, gender, region of residence, income level, underlying health conditions and nationality. 

The study has involved millions of people over the age of 16 vaccinated against SARS-CoV-2 between February and July, 2021. 

24,823,976 doses have been administered to date, of which 13,163,094 are people who have received a single dose vaccine or the first dose in a series and 12,167,623 are those who have completed their vaccination program. The numbers represent 87% and 80% of the respective target populations to be vaccinated. 

Dr. Rafael Araos, one of the investigation’s lead researchers, explained that “the most important aspect of the investigation is that it studied the effects on a cohort, a group of people monitored over time who have or have not been exposed to a vaccine. Relevant variables were adjusted and the occurrence of events was compared among groups, according to their exposure.” 

Describing the statistical method, Dr. Araos said that three elements were considered: 

1. the Hazard Risk (HR) for each group and outcome, using an extension of Cox’s proportional hazards model. 

2. Effectiveness: 100% x 1 – HR 

3. Effectiveness adjusted for age, sex, region of residence, income level, comorbidities and nationality. 

Dr. Araos mentioned three important strengths of the investigation for each of the vaccines assessed: 

1. Data collection and analysis 

- Fast results allow the short-term effectiveness to be assessed in “real time”. 

2. Robust database 

- Identification and evaluation of clinically relevant results. 

- Adjustment for covariables.

3. Sample size 

- Representativeness.

- Estimation of effectiveness on partially and fully immunized individuals. 

4. Monitoring over time: allows estimate of duration of effect 

SINOVAC 

Regarding the Sinovac vaccine, effectiveness results 14 days after the second dose, among a cohort of 8,600,000 individuals over the age of 16 affiliated to FONASA (National Health Service) were: 

58.49% effectiveness in preventing symptomatic COVID-19

86.02% effectiveness in preventing hospitalization

89.68% effectiveness in preventing ICU admission

86.38% effectiveness in preventing death

PFIZER-BIONTECH

Regarding the Pfizer-BioNTech vaccine, effectiveness results 14 days after the second dose, among a cohort of 4,500,000 individuals over the age of 16 affiliated to FONASA were: 

87.69% effectiveness in preventing symptomatic COVID-19

97.15% effectiveness in preventing hospitalization

98.29% effectiveness in preventing ICU admission

100% effectiveness in preventing death

ASTRAZENECA

Regarding the AstraZeneca vaccine, effectiveness results 14 days after the second dose, among a cohort of 2,380,000 individuals over the age of 16 affiliated to FONASA were: 

68.68% effectiveness in preventing symptomatic COVID-19

100% effectiveness in preventing hospitalization

100% effectiveness in preventing ICU admission

100% effectiveness in preventing death

Conclusions

Dr. Araos concluded, “the CoronaVac vaccine continues to demonstrate important signs of effectiveness against SARS-CoV-2 regarding hospitalization, ICU admission and death. However, its effectiveness in preventing the disease falls from 67% to 58.49%. It is therefore a good time to discuss a booster shot.” 

Regarding Pfizer-BioNTech, he added, “(this vaccine) also shows a decrease in protecting against COVID-19, but it remains stable among the other variables analyzed. It shows good numbers in preventing hospitalization, ICU admission and death.” 

In the case of AstraZeneca, Dr. Araos indicated that analysis revealed 100% effectiveness in preventing hospitalization, ICU admission and death. However, the vaccine has been monitored over less time and results must be confirmed in the future. 

The researcher stated that the results allow us to declare that “the public can rest assured with the country’s available pool of SARS-CoV-2 vaccines because they are especially effective in preventing hospitalization, ICU admission and death due to COVID-19.”