Cristina Azevedo (Fiocruz News Agency)
A new study published in Nature Communications last Thursday (28/11) shows that two doses of the AstraZeneca vaccine, produced in Brazil by Fiocruz, provide high protection against the Gamma variant in people above 60 years old. Based on São Paulo, the research shows that the second dose increases protection against death by about 30% when compared to the first dose, reaching an effectivity of 93.6%. Carried out by 20 researchers in Brazil, the United States and Spain, the study called Effectiveness of the ChAdOx1 vaccine in older adults during the circulation of the Gamma variant in São Paulo highlights to health authorities the need to go after elderly subjects who have missed their vaccination appointment and complete their vaccination scheme.
The research was coordinated by Julio Croda, researcher of Fiocruz Mato Grosso do Sul, and aims to respond to the scarcity of data on the effectiveness of AstraZeneca among the elderly population in countries with high prevalences of Gamma, the variant first identified in Manaus. The study, therefore, chose the state of São Paulo, the country’s most populated state, which went through three waves of the Covid-19 epidemic, with more than 3.89 million cases and 130 thousand deaths up to July 9. The Gamma variant increased in circulation during the second and the third waves, reaching a prevalence of 80.2% between March and May this year.
“We know that elderly people face the issue of immunosenescence [alterations of the immunological system caused by ageing], but this analysis in people above 60 years old shows that even in the context of circulating Gamma variant, the full vaccination scheme provides good protection. Hence the need to find all those who have not yet completed their vaccination and make sure they take both doses”, highlighted Croda.
Previous clinical trials in other countries already showed a certain drop in effectiveness of the first dose of the vaccines against the new variants of concern (VoC). This was one of the motives for this research in Brazil, involving the Gamma variant.
Of 137,744 individuals eligible for the study, 61,164 were selected and submitted to an RT-PCR test in the so-called negative test, which begins with patients who tested positive for COVID-19 and compares them with patients who did not test positive.
The research shows that 28 days after the first dose, effectiveness was 33.4% against symptomatic COVID-19, 55.1% against hospitalization, and 61.8% against death among the elderly. A new measurement 14 days after the second dose showed that effectiveness jumped to 77.9% against symptomatic disease, 87.6% against hospitalization, and 93.6% against death. “Completing the immunization of the ChAdOx1 [AstraZeneca] vaccine provides significantly higher protection when compared with a single dose against mild and severe COVID-19 in elderly individuals during the wide circulation of the Gamma variant”, states the study.
Croda mentions that “in general, effectiveness was 76% with the first dose to prevent symptomatic disease”. “We recorded less than that, but this is what is being reported throughout the world for the new variants, especially the Beta, the Gamma and the Delta ones: a loss of effectiveness, of protection against the symptomatic form [with the first dose only]”, he said. “The good news is that with two doses this effectiveness is extremely high against death. It reaches almost 95%. These are therefore very positive data, showing that the Fiocruz vaccine still works, including in this context of a new variant, the Gamma”, he added.
He also coordinated the research involving the effectiveness of the Coronavac vaccine in elderly people in São Paulo during the circulation of the Gamma variant, published in August. The work evaluated more than 55,000 people above 70 who were given RT-PCR tests for COVID-19 between January 17 and April 29, 2021, showing an effectiveness of 61.2% against death. The researcher, however, emphasizes that the surveys must not be compared to one another, because the cohort is different, with CoronaVac, which began being applied earlier, being used on people who are 80 to 90.
Scenario with the Delta
The results of the new study are consistent with the reduced effectiveness of the first dose of Pfizer and AstraZeneca shown in the United Kingdom with the new variants. “In the specific context of the emergence and dissemination of VoC, national programs should take into account the reduced effectiveness of the first dose against the Gamma and Delta variants of concern in the elderly, together with limitations of the supply of vaccines, speed of vaccination, and logistics when quantifying the benefits in the strategy of the interval between the doses”, says the text.
The Fiocruz researcher observes that even when facing the advance of the Delta, the AstraZeneca vaccine seems to remain effective. “If there were a change, we would be seeing an increase in the number of cases and an acceleration in the number of deaths. And we have not seen any of this so far. Rio was the epicenter of the Delta, and the trend is that of a reduction of hospitalizations and deaths. I believe that vaccines still work for the Gamma and the Delta”, said Croda. “The Delta has not been around for long. We need two or three more months of predominance of this variant to do this same type of evaluation”.
The study relied on the participation of researchers Matt D.T. Hitchings, Otavio T. Ranzani, Murilo Dorion, Tatiana Lang D’Agostini, Regiane Cardoso de Paula, Olivia Ferreira Pereira de Paula, Edlaine Faria de Moura Villela, Mario Sergio Scaramuzzini Torres, Silvano Barbosa de Oliveira, Wade Schulz, Maria Almiron, Rodrigo Said, Roberto Dias de Oliveira, Patricia Vieira da Silva, Wildo Navegantes de Araújo, Jean Carlo Gorinchteyn, Jason R. Andrews, Derek A.T. Cummings, Albert I. Ko and Julio Croda – the latter two from the Gonçalo Moniz Institute (Fiocruz Bahia) and Fiocruz Mato Grosso do Sul. The remaining researchers work at institutions such as the University of Florida, the Global Institute for Health of Barcelona, the University of São Paulo, and the Pan-American Health Organization (PAHO), among others.