The greater efficacy of the half dose of the Oxford Covid vaccine has not yet been definitively explained; search for answers | Vaccine

Experts believe that it is too early to pin down why and what the end result should be.

Oxford Vaccine Group director Andrew Pollard said in an interview with the BBC that the cause of the result was “intriguing.”

“This 90% is an intriguing result. I think it’s a really exciting and intriguing result that we need to dig into,” he said.

For the scientific journal “Nature”, virologist Luk Vandenberghe, from Harvard University in Boston, said that he believes that the data is not enough to evaluate the difference between the two doses, and that these differences should disappear when more cases are detected of the new coronavirus patients already vaccinated.

In an interview with G1, Jorge Elias Kalil Filho, from the University of São Paulo and part of the US monitoring committee for clinical studies of vaccines against Covid-19, affirms that the number of infected patients after the application of the vaccine is low.

“The numbers are very small. This lower-dose group shouldn’t have more than 30 Covid cases. I don’t have an explanation,” he says. Kalil advocates dissemination and analysis with more data to understand the relationship between efficacy and dose.

Along the same lines, the infectious diseases doctor Pedro Folegatti, who leads the development of the Oxford and AstraZeneca vaccine, assures that “it is not worth speculating on the reasons” and that “we may have more information ahead”. .

This vaccine uses a manufacturing process (platform) called a viral vector. Scientists place a protein from the new coronavirus (Sars-CoV-2) inside another virus (in the case of the Oxford vaccine, an adenovirus), which will carry it into the body.

The protein used in the vaccine, protein S, is important because it is what the virus uses to infect cells. The goal is that, from this protein, the body can build a defense if it comes into contact with the new “real” coronavirus.

Although it is too early to create theories about the dose, as Folegatti argues, some scientists believe that the response mechanism is not only linked to protein S, but also to adenoviruses, which can hinder the action and development of the immune response .

“When we work with a vector, we can have a reaction to the vector, which must be what happened here. Less exposure to the vector in the first dose [de meia dose em vez da dose completa] it can guarantee a less reaction in the second dose and a greater reaction to the protein peak (S), which is what we want ”, explains Natália Pasternak, a microbiologist at the University of São Paulo (USP).

Denise Garrett, vice president of the Sabin Vaccine Institute, adds the explanation: “And, if you have too much of the viral vector, our immune system can attack the vector before it releases the Spike (S) protein. [ativação do sistema imune] it would be more due to the vector virus than the coronavirus antigen ”.

Key points from the Oxford vaccine announcement:

• The vaccine was 90% effective when given in a half dose followed by a full dose at least a month apart, according to data from tests in the UK and Brazil. That was the lowest dose regimen, which was an advantage for the researchers, because it means that more people can be vaccinated.
• When administered in 2 full doses, the effectiveness was 62%.
• The analysis that considered the two types of doses indicated an average efficacy of 70.4%.
• Andrew Pollard, Director of the Oxford Vaccine Group, said andstar optimistic that the immune response generated by the vaccine will last at least a year.
• 131 cases were recorded among volunteers: 101 among those who received placebo (inactive substance) and 30 among those who received the vaccine. There were no severe cases of the disease among those who received the vaccine.
• To arrive at the results, the researchers analyzed data from 11,636 vaccinated people. Of these, 8,895 received the two full doses and 2,741 received the dose followed by a half full dose.
• A AstraZeneca expects to have 200 million doses ready by the end of 2020 and 700 million doses by the end of the first quarter of 2021, worldwide.
• A The vaccine can be stored, transported and handled under normal refrigeration conditions (2 ° C to 8 ° C) for at least 6 months. (This is an advantage over the candidate Pfizer, which must be stored at -70ºC during transport, and Moderna, which must be kept at -20ºC).

VIDEOS: vaccine news