Research by the National Health Institute Doctor Ricardo Jorge (INSA) showed that vaccines that use mRNA technology, such as those from Pfizer and Moderna laboratories, are less effective against the Delta variant of SARS-CoV-2.
According to a statement from INSA, there is a "significantly higher probability of infection by the Delta variant in vaccinated people," doubling "the risk of infection by the Alpha variant" of the new coronavirus, which causes COVID-19.
The INSA scientists found, after analyzing about 2,000 cases, that the drop in immunity occurs in either people with one dose or two doses of mRNA vaccines.
"According to the results obtained, it was observed that those infected with the Delta variant had, on average, higher viral load values, which could mean greater transmissibility," said the note from the Institute.
According to the research, which is being prepared to be published in scientific journals, the effectiveness of the complete vaccine schedule, which was up to 90 percent for the Alpha variant, drops to between 41 percent to 80 percent with the Delta variant.
On the other hand, the Portuguese researchers also concluded that those vaccinated have "a lower viral load and potentially lower transmissibility than unvaccinated individuals," regardless of the coronavirus variant.
The study was conducted between May and July 2021, when the Delta variant became prevalent in Portugal, reaching 98.9 percent of new COVID-19 infections, according to data released by the INSA.
The pandemic has caused 17,645 deaths in Portugal, out of a total of 1,020,546 confirmed cases of COVID-19 since March 2020, according to data from the Portuguese health authorities.