The vaccine is given by intramuscular injection into the deltoid muscle. The initial course consists of two doses. The World Health Organization (WHO) recommends an interval of 4 weeks between doses, with data from Chile suggesting that a longer interval provides more robust immunity. Early evidence suggests that immunity wanes rapidly, so a booster dose after the initial course might be needed. Effectiveness In Brazil, a study was conducted in Serrana, population 45,000, where authorities attempted to vaccinate the entire adult population with<unk> . After 75% of the adult population received the vaccine, preliminary results show deaths fell by 95%, hospitalizations by 86% and symptomatic cases by 80%. According to Ricardo Palacios, a director at São Paulo's Instituto Butantan, “The most important result was understanding that we can control the pandemic even without vaccinating the entire population.” In July 2021, researchers from the Chilean Ministry of Health published a paper containing real-world data for their vaccination campaign. The study was conducted between 2 February and 1 May 2021, consisting of 10.2 million people. The effectiveness of<unk>  vaccine after the second dose was in preventing symptomatic disease, for hospitalization, for ICU admission, and in preventing COVID-19 related deaths. The effectiveness after the first dose was against symptomatic disease, against hospitalization, against ICU admission, and against deaths. The study concluded that the vaccine was effective in preventing COVID-19. In May 2021, real-world data from Indonesia showed the vaccine was highly effective, with 94% of inoculated health care workers protected against symptomatic infection by the vaccine, besting results of clinical trials. In this study of 128,290 health workers in Jakarta, less than 1% of the vaccinated healthcare workers contracted symptomatic COVID-19, compared to more than 8% among the unvaccinated healthcare workers. The vaccine reduced the risk of hospitalization and death of the inoculated medical workers by 96% and 98% respectively. Uruguay released real-world data based on 795,684 people who have received both doses of<unk>  for more than 14 days as of 1 June 2021. In this group, 8,298 tested positive, 45 were admitted to the ICU, and 35 died of COVID-19. This indicated 64.52% and 61.47% effectiveness in reducing COVID-19 cases for people aged 18–49 and 50 and older respectively. The vaccine was 94.95% and 92.18% effective in reducing ICU admissions, and 95.35% and 95.2% effective to prevent deaths. Among fully-vaccinated healthcare professionals, the vaccine was 66% effective in preventing cases, and 100% effective in preventing ICU admissions and deaths. Preliminary results from a test-negative case-control study from 19 January to 13 April 2021 in Manaus suggest that, after just one dose, the vaccine is effective against asymptomatic infections and against symptomatic disease. The one-dose group consisted of 53,176 healthcare professionals. During the study, 66% of the samples were of the Gamma variant. The same study found paradoxically reduced effectiveness against symptomatic disease in another group that received two doses, an effect attributed by the authors to unmeasured confounding leading to downward bias in the efficacy estimate. In Chile, the effectiveness against symptomatic disease dropped from 67% between February–April 2021 to 58.5% in early July. Because of this, on 11 August, Chile began giving an additional dose of the Oxford–AstraZeneca vaccine to people over 55 who were fully vaccinated with<unk>  before 31 March. In October 2021, a large scale study in Chile with 2,017,878 participants reported that, with a<unk>  booster, effectiveness against hospitalization increased from 84% to 88% and effectiveness against symptomatic disease increased from 56% to 80%. The greatest increases were seen with a heterologous Oxford–AstraZeneca vaccine booster, resulting in 96% effectiveness against hospitalization and 93% against symptomatic disease. A study by the University of Hong Kong in December 2021 found that a third dose of<unk>  does not provide sufficient protection against the Omicron variant, directly contradicting the vaccine manufacturer's claim and a study by the Pontifical Catholic University of Chile that it does. Variants In the following tables, a vaccine is generally considered effective if the estimate is ≥50% with a >30% lower limit of the 95% confidence interval. Effectiveness is generally expected to slowly decrease over time. +Initial effectiveness by variant Doses Severity of illness Delta Gamma 1 Asymptomatic Symptomatic Hospitalization 2 Asymptomatic Symptomatic Moderate Hospitalization In the elderly A test-negative case-control study from 17 January to 29 April 2021 in the state of São Paulo, during which 86% of the collected genotype isolates were of the Gamma variant, with 43,774 participants aged 70 years or older, found an effectiveness after two doses of against symptomatic disease, against hospitalization and against death. After a single dose, the effectiveness was only against symptomatic disease, against hospitalization and against death, highlighting the importance of receiving the second dose. The study also found that effectiveness against symptomatic disease decreased with increasing age: +Initial effectiveness in old age after two doses (Brazil) Severity of illness Age 70–74 Age 75–79 Age ≥80 Symptomatic Hospitalization Death Preliminary data from a large effectiveness study in Brazil with 61 million individuals from 18 January to 30 June 2021, when the Gamma variant was dominant in the country, indicate that effectiveness is markedly reduced in those aged 90 or older, attributable to immunosenescence: +Initial effectiveness by age (Brazil) Doses Severity of illness Age <60 Age 60–69 Age 70–79 Age 80–89 Age ≥90 1 Asymptomatic Hospitalization Death 2 Asymptomatic Hospitalization Death Specific populations On 21 October 2021, the WHO recommended a third dose as part of the initial course for older adults 3–6 months after the second dose and for immunocompromised individuals 1–3 months after the second dose because these groups mount a weaker immune response compared to healthy adults. Where supplies are limited, the third dose for seniors should be given after achieving high coverage with two doses.
CoronaVac
EpiVacCorona
TroVax
Vaccitech
ImmunoGen
Cevira
MenAfriVac
Winpepi