Most vaccines administered to the population to combat covid-19 and its variants, from 'alpha' to 'delta', are double-dose. But, with the emergence of the 'omicron' variant, some are already moving towards taking a third dose, called a 'booster dose', even of a different brand from the previous two doses.

The existing vaccines, according to experts, may not have the expected effectiveness in combating the new variant. In this sense, the United Kingdom (UK) confirmed on Monday that it will accelerate the program of booster vaccines against covid-19. This will be administered in adults, and will also be recommended for young people over the age of 12. In addition, the UK will reduce the interval to three months after the second dose.

Since pharmaceutical companies do not guarantee a mass distribution of the vaccines effective against the new variant until the next hundred days, the UK argued that these measures "will protect more people more quickly." On the other hand, the decision poses a logistical challenge, as it will almost double the number of people eligible for the booster dose.

Regardless of the "ineffectiveness" of existing vaccines "[they] remain our best line of defense against this virus...it is very unlikely that they will have no effect against severe symptoms," said Health Minister Sajid Javid.

Among the vaccines on the market, the UK's Joint Committee on Vaccination and Immunization (JCVI) suggests using Pfizer and Modern vaccines.

The UK has already identified 11 cases of infection with the Omicron variant, six of them in Scotland, and the numbers are expected to increase in the coming days.

So far, Portugal has administered 990,192 booster doses against Covid-19, and is close to reaching one million people vaccinated with the third dose, reveals the daily vaccination report shared by the local Directorate-General of Health. More than half of people (500,196) who took the booster dose are over the age of 80.

"Booster dose" is of a different brand than double dose

The covid-19 variants catalogued by the World Health Organization have always worried governments, but not to the point of advising the population to administer any vaccine, especially for the double dose ones. The indications have always been to take the same brand of vaccine.

In Brazil, for example, the Municipality of São Paulo announced yesterday that, starting today, it will use the Pfizer vaccine for the booster dose of those who were immunized with Janssen. The recommendation of the Brazilian Ministry of Health is to use the same brand vaccine. However, a previous recommendation, made in August this year, already authorized the use of the Pfizer vaccine for seniors who had taken the single dose of Janssen.