Research suggests higher risk of reinfection by the Delta variant

A recently published study, with the participation of the Oswaldo Cruz Foundation - Fiocruz, suggests that the Delta variant of the new coronavirus, first detected in India, may increase the risk of reinfection. The research shows that the serum of people previously infected by other strains is less powerful against this viral variant. The problem is markedly observed among individuals previously infected by the Gamma variant, originally identified in Manaus, Brazil, and currently the dominant strain in the country, as well as by the Beta variant, first detected in South Africa. In these cases, the ability to neutralize the Delta strain is eleven times smaller.

The blood serum of vaccinated people also has less power against the Indian-originated variant, but data shows that vaccines are still effective. The neutralizing ability is 2.5 times smaller for Pfizer’s vaccine and 4.3 times smaller for AstraZeneca. The authors of the study highlight that the rates are similar to those verified for the Gamma and Alpha variants, which emerged in Brazil and in the United Kingdom, respectively. There is no evidence of generalized neutralization escape, unlike what has been observed with the Beta variant, originally from South Africa.

“Based on these results, it seems likely that current RNA and viral vector vaccines will still provide protection against the B.1.617 lineage [which has three sub-lineages, including the Delta variant], although an increase in infection rates may occur as the result of the reduced neutralization ability of the sera”, state the researchers in the paper.

The study was published in Cell journal. Led by the University of Oxford, in the United Kingdom, the study was the result of a great scientific collaboration involving 59 researchers from the United Kingdom, China, Brazil, United States, South Africa, and Thailand. In Brazil, researchers from the Measles and Respiratory Virus Laboratory of the Oswaldo Cruz Institute (IOC/Fiocruz), the Laboratory of Ecology of Communicable Diseases in the Amazon of the Leônidas & Maria Deane Institute – Fiocruz Amazônia, and the Foundation for Health Surveillance of the state of Amazonas (FVS/AM) took part.

Divergent strains

The Delta variant is a subtype of the B.1.617 viral lineage, which emerged in India in October 2020. In May this year, after being associated with a worsening of the pandemic in India and in the United Kingdom, the strain was declared a variant of concern by the World Health Organization (WHO). According to the WHO, the variant currently circulates in at least 85 countries in the world. In addition to that, nine countries have sequenced viruses of the B.1.617 lineage, without identifying the viral sub-lineage.

In Brazil, infections caused by the Delta variant were diagnosed in travelers in the states of Maranhão, Rio de Janeiro, Minas Gerais, Paraná and Goiás, according to the Ministry of Health. On June 19th, the Municipal Secretary of Health of Goiânia confirmed the first record of local transmission of the strain.

Like other variations of concern, the Delta strain has mutations in the region of the genome responsible for guiding the production of the spike protein of the new coronavirus, the so-called S protein. This molecule, located on the surface of the viral membrane, forming the crown of the virus, is responsible for the first step of the infection process: adhesion of the virus to the cells. For this reason, it is the target of the most powerful antibodies produced by the body to neutralize Sars-CoV-2.

According to the scientists, mutations in the S protein can be positive for the virus in two different ways. One one hand, it can increase the capacity of adhesion to the receptors present in the host’s cells, leading to higher transmissibility. On the other, it can modify the region of the S protein to which antibodies bind, allowing the virus to escape from the host’s immune system.

The analysis of the new study show that the affinity of the Delta variant for cellular receptors is higher than that observed in the lineages that were circulating early on in the pandemic. However, it is lower than that verified in other variants of concern. On the other hand, the variant that originated in India has an antigenic profile that diverges quite a bit from the other viruses already studied.

To get to this result, researchers analyzed the action of 113 sera, obtained from infected and immunized patients, on six strains of the new coronavirus. The strains are a lineage very close to the virus initially detected in Wuhan, China, at the beginning of the pandemic; the Alpha, Beta, Gamma and Delta variants of concern; the variant of interest Kappa, closely related to the Delta variant and also a subtype of the B.1.617 lineage.

The methodology allows for the mapping of the antigenic space of the different strains. In addition to confirming the expressive shift of the Delta variant from the Gamma and Beta ones, the analysis also revealed the central position of the Alpha strain, originally from the United Kingdom. According to the scientists, the findings show that vaccines based on the Alpha variant offer wide protection against the current variants, which may be a relevant piece of information for the formulation of new vaccines.

“It is looking more and more likely that more than one variant may be needed to provide protection as the serological complex of the Sars-CoV-2 continues to evolve. We suggest that one component will likely continue to include strains related to Wuhan or B.1.1.7 [Alpha variant], as at least up to this moment they seem to be more centrally positioned in the serological complex, being able to provide protection against multiple viral strains”, says the researchers in the paper.