Effectiveness of the CoronaVac vaccine in older adults during a gamma variant associated epidemic of covid-19 in Brazil: test negative case-control study

Abstract

Objective To estimate the effectiveness of the inactivated whole virus vaccine, CoronaVac (Sinovac Biotech), against symptomatic covid-19 in the elderly population of São Paulo state, Brazil during widespread circulation of the gamma variant. Design Test negative case-control study. Setting Community testing for covid-19 in São Paulo state, Brazil. Participants 43 774 adults aged ≥70 years who were residents of São Paulo state and underwent reverse transcription polymerase chain reaction (RT-PCR) testing for SARS-CoV-2 from 17 January to 29 April 2021. 26 433 cases with symptomatic covid-19 and 17 622 test negative controls with covid-19 symptoms were formed into 13 283 matched sets, one case with to up to five controls, according to age, sex, self-reported race, municipality of residence, previous covid-19 status, and date of RT-PCR test (±3 days). Intervention Vaccination with a two dose regimen of CoronaVac. Main outcome measures RT-PCR confirmed symptomatic covid-19 and associated hospital admissions and deaths. Results Adjusted vaccine effectiveness against symptomatic covid-19 was 24.7% (95% confidence interval 14.7% to 33.4%) at 0-13 days and 46.8% (38.7% to 53.8%) at ≥14 days after the second dose. Adjusted vaccine effectiveness against hospital admissions was 55.5% (46.5% to 62.9%) and against deaths was 61.2% (48.9% to 70.5%) at ≥14 days after the second dose. Vaccine effectiveness ≥14 days after the second dose was highest for the youngest age group (70-74 years)—59.0% (43.7% to 70.2%) against symptomatic disease, 77.6% (62.5% to 86.7%) against hospital admissions, and 83.9% (59.2% to 93.7%) against deaths—and declined with increasing age. Conclusions Vaccination with CoronaVac was associated with a reduction in symptomatic covid-19, hospital admissions, and deaths in adults aged ≥70 years in a setting with extensive transmission of the gamma variant. Vaccine protection was, however, low until completion of the two dose regimen, and vaccine effectiveness was observe to decline with increasing age among this elderly population.

Effectiveness of Primary and Booster COVID-19 mRNA Vaccination against Omicron Variant SARS-CoV-2 Infection in People with a Prior SARS-CoV-2 Infection

“…We chose the TNCC design because it has been shown to provide effectiveness estimates consistent with those from randomized control trials, has been widely applied to estimate real-world effectiveness for COVID-19 vaccines, and mitigates the risk of confounding introduced by care-seeking and testing access. 1,12–15…”

“…We chose the TNCC design because it has been shown to provide effectiveness estimates consistent with those from randomized control trials, has been widely applied to estimate real-world effectiveness for COVID-19 vaccines, and mitigates the risk of confounding introduced by care-seeking and testing access. 1,[12][13][14][15] The study population comprised vaccine eligible (≥5 years of age) people who had at least one SARS-CoV-2 test or mRNA (mRNA-1273 [Moderna] or BNT162b2 [Pfizer]) vaccine dose in the medical records. We identified SARS-CoV-2 RT-PCR tests that were collected from the study population and performed with the TaqPath™ COVID 19 (Thermo Fisher Scientific) diagnostic assay between November 1, 2021 and January 31, 2022, the period prior to and during the Omicron epidemic wave in Connecticut (Figure 1A).…”

Covid-19 vaccine effectiveness against general SARS-CoV-2 infection from the omicron variant: A retrospective cohort study

“…27,28 On the surface, our findings of higher protection in older university employees relative to younger university students appear to contradict evidence that Covid-19 vaccines are (relatively) less protective in older adults. 29,30 However, the risk of infection is dependent on the size of the infecting dose of the virus (i.e., viral load). [31][32][33][34][35][36] Compared to the average adult, university students typically engage in more frequent and higher-density social interactions.…”

An overview on inactivated and live‐attenuated SARS‐CoV‐2 vaccines

“…Also, the effectiveness against hospital admissions and deaths was 55.5% and 61.2%, respectively, at ≥14 days after the second dose. 29 Cerqueira‐Silva investigated the influence of age on CoronaVac effectiveness and the duration of protection in 75,919,840 Brazilian cases from January 18 to July 24, 2021. Based on their results, vaccination with CoronaVac was effective against SARS‐CoV‐2 infection and highly efficient against hospitalization, ICU admission, and death in individuals up to 79 years.…”