"We are not describing anything that was not anticipated, but it makes us happy to see that it worked and gives us confidence that it is worth the vaccine. The vaccination process must go as quickly as possible," Tiago Guimarães said when describing to journalists a study being carried out at São João Hospital on the immunity rate of the vaccine against Covid-19.

Of the 2,125 doctors, nurses, operational assistants and diagnostic and therapeutic technicians who took the vaccine on 27 December - the date of the launch of the National Vaccination Plan - around four dozen were subjected to serological tests aimed at studying immunity.

Tiago Guimarães stressed that these tests are different from the more common tests, since they show "generally the antibodies produced after an infection," while those used in the study measure "the capacity to produce antibodies induced by the vaccine.

Three samples were taken - the first in the days after the vaccine was taken, the second in the following week and the third after 15 days - and the study found that "95-97 percent of people already produce antibodies, so it is presumed that they have immunity".

"Virtually all people have produced antibodies through the vaccine at least after 15 days. At the second harvest, 10 to 15 percent already had [antibodies induced by the vaccine]. The aim is to see how long the antibodies appear," explained the expert.

"It does not call into question the need for the second dose [with the European Medicines Agency recommending the second dose at 21 to 42 days after the first, i.e. three to six weeks] but it does give us a window of time so that the second dose can be taken properly," the director said.