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Study shows good protection after 2 doses of the AstraZeneca vaccine


21/09/2021

Cristina Azevedo (Fiocruz News Agency)

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A Swedish study with people infected by the Sars-CoV-2 and with subjects immunized with the Oxford/AstraZeneca (produced in Brazil by Fiocruz), Pfizer/BioNTech vaccines, and with people who were given one dose of each vaccine shows good protection 12 months after vaccination, against the so-called variants of concern. Submitted as preprint (without peer review), the research shows that two doses of the AstraZeneca vaccine result in the smallest reduction in effectiveness in neutralization assays against the Gamma and Beta variants, those with the most significant drops in effectiveness in all scenarios evaluated.

AstraZeneca vaccine is produced in Brazil by Fiocruz (Photo: Bernardo Portella-Biomanguinhos/Fiocruz) 

The appearance of variants of the Sars-CoV-2, such as Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1) and Delta (B.1.617.2), caused concern on the effectiveness of neutralizing antibodies (NAb) induced by infections by the original strain or by vaccines based on the spike protein of the Sars-CoV-2, as this protein is directly associated to the virus’ ability to enter human cells. The study Neutralization of variants of concern, including Delta, one year after COVID-19 infection or vaccination aimed to determine the presence of IgG antibodies and neutralizing antibodies against variants, in the long term.

Good response against Delta

The research discovered that antibodies against the wild-type spike, as well as neutralizing antibodies, remained detectable in 80% of participants even one year after a mild infection (non-vaccinated). The neutralizing capacity was similar against the native strain (used as reference), Alpha (0.95) and Delta (1.03, i.e. an even better response when compared with the standard, which is response against the original strain 1), but significantly reduced against Beta (0.54) and Gamma (0.51).

Similarly, two doses of Pfizer or two doses of AstraZeneca allowed for a sustainable capacity against Alpha and Delta — 1.01 and 1.03, and 0.96 and 0.82, respectively — one year after vaccination. However, reduced capacity was observed against Beta (0.67 and 0.53) and Gamma (0.12 and 0.54). The regimen that consists of two doses of AstraZeneca shows a significantly smaller reduction in response against the Gamma variant, which has had great impact during the COVID pandemic in Brazil.

The combination of AstraZeneca and Pfizer also showed a reduction in effectiveness against variants of concern (0.74 and 0.70) Alpha and Delta, and more remarkably against the Beta and Gamma variants (0.29 and 0.13). In a comparison between all regimens, the AstraZeneca combination showed a more consistent response against variants of concern, when compared with the response of patients recovering from COVID-19 and with the other regimens evaluated in the study (Pfizer/Pfizer and/or Pfizer/AstraZeneca).

The discoveries on the long-term neutralization against the Alpha and Delta variants, both wildly diffuse, one year after infection by the original strain, may help authorities create vaccination strategies in cases of a scarcity of supplies, according to the study. The results suggest the need for even more precaution against the Beta and Gamma variants, in an effort to optimize the next generations of vaccines.

Tests every four months

Between April 15th and May 8th, 2020, 2,149 health workers of the Danderyd Hospital, in Stockholm, Sweden, were enrolled in the study. They were invited to repeat their blood tests every four months. Two types of tests were used: one that measured IgG in response to the spike protein and the other evaluating not only IgG in response to the spike protein, but also neutralizing capacity against the original strain and its four variants.

This sub-study included a group made up of subjects who had tested positive in both tests, subjects who had undergone the follow-up tests, and those not yet vaccinated, during this 12-month period. All participants reported mild symptoms and none needed to be hospitalized. Blood tests were also done for the three vaccinated groups: those with two doses of Pfizer, those with two doses of AstraZeneca, and those with one dose of each vaccine, in the study approved by the Swedish Ethical Review Authority.

“Both vaccines used in the study are based on the wild-type Sars-CoV-2 spike protein. We found that these three vaccination regimens yielded similar response as infection with the wild-type strain”, says the study. “Up to this moment, it has been reported that the E484 mutation affects the link between antibody and neutralization, which means that both the Beta and the Gamma strains may escape the immunological control induced by the original strain or by the current vaccines”. These results may help define the most suitable vaccination schemes against the new variants of the virus.

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