University of São Paulo: After a second dose, CoronaVac has an average effectiveness of 42% in people over 70 years old, shows a study done in SP

The CoronaVac vaccine is 42% effective after 14 days of applying the second dose in people with an average age of 76 years. The number was obtained in an international study, with the participation of USP, carried out in 15,900 people aged 70 or over in the State of São Paulo. Research also shows that the effectiveness of the coronavirus vaccine decreases with age, being less after 80 years, and taking only the first dose does not offer protection against covid-19. The researchers recommend that vaccination programs guarantee the second dose of the vaccine, and that people continue to practice protective measures, such as wearing masks and avoiding crowds.

The conclusions of the work are in a preprint (previous version of a scientific article) published on the medRxiv website on May 21. “The research evaluated the effectiveness of the CoronaVac vaccine against symptomatic infections by sars-cov-2 in the population aged 70 or over in the State of São Paulo, in a context where most infections are due to the P.1 variant, that is, it verified if the vaccine protects against symptomatic infections in real life ”, explains epidemiologist Otávio Ranzani, first author of the article. “Effectiveness was also assessed by age groups and previous infection.”

The study covered the period between January 17 and April 29, when vaccination with a two-dose schedule of CoronaVac was implemented in São Paulo. “We identified cases of covid-19 confirmed by the RT-PCR test that had symptomatic disease with cases of tested people who tested negative for the disease, using data from national surveillance systems and the state vaccination database,” reports the epidemiologist. “The cases and negative tests were matched for age, sex, race, municipality, previous condition for covid and date of the RT-PCR test, and from these numbers we estimated the effectiveness of the vaccine, adjusted for age and comorbidities.”

Among 26,433 cases of covid-19 and 17,622 people with a negative test, 7,950 pairs were selected, generating a total of 15,900 individuals evaluated with an average age of 76 years. “We found that the overall effectiveness of the vaccine was 42% after 14 days of the second dose in a population with an average age of 76 years,” says Ranzani. “The overall effectiveness drops with age, being higher in people under 75 years old and lower after 80 years old. In an exploratory analysis, we found that effectiveness reaches 50% after 28 days of the second dose in the population aged 70 and over. ”


According to the epidemiologist, the loss of effectiveness observed in the study was already expected. “The immune system is not optimal with advanced ages, the presence of other diseases, that is, comorbidities and other aspects, in a process that we call immunosenescence”, he says. “This is true for other vaccines as well.”

The research found no protective effect on the first dose of the vaccine, which, according to the doctor, is an important finding for immunization programs. “It is necessary that the programs guarantee the second dose of CoronaVac, in the recommended time, for everyone”, he highlights. “The programs should plan to optimize the vaccination of the elderly from the age of 80 and fragile, whether with reinforcement or changing the type of vaccine, but this still needs to be studied.”

CoronaVac can be more efficient when applied with an interval between doses greater than 21 days

Study with health professionals shows the effectiveness of Coronavac
Based on the results of the study, the doctor recommends that protective measures such as masks, maintaining ventilated environments and avoiding crowding should continue until we have better control of the epidemic. The work is described in the preprint Effectiveness of the CoronaVac vaccine in the elderly population during a P.1 variant-associated epidemic of COVID-19 in Brazil: A test-negative case-control study , published on the medRxiv website on May 21.

In Brazil, the research had the participation of USP, Fundação Oswaldo Cruz (Fiocruz), University of Brasília (UnB), Federal University of Mato Grosso do Sul (UFMS), State University of Mato Grosso do Sul (UEMS), National Institute of Science and Technology in Health Technology Assessment (INCT-IATS) and Health Secretariat of the State of São Paulo. Researchers from the Pan American Health Organization (PAHO), the Barcelona Institute of Global Health (Spain), the University of Florida, Yale University and Stanford University (United States) were also part of the project team.

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