Sergi stands atop a wooden tower from where he can see almost the entire Llobregat Delta. However, he never takes his eyes off the binoculars he wears around his neck, which he uses to inspect the area. He joined the Rural Agents less than three years ago, and one of his tasks is to monitor this area, declared a natural interest site near El Prat Airport.

The WHO this week called for no third dose - or booster or reminder dose - until at least 10 per cent of the world's population is vaccinated. Even so, countries such as Israel have already started injecting it into immunocompromised patients and people over 60, and France and Germany announced Thursday that they will also give it to the elderly and the most vulnerable. Spain is also considering this option: the Minister of Health, Carolina Darias, said that "everything indicates that the third dose will have to be administered" - although she did not specify whether to certain groups or to the general population - and the Secretary of Public Health of the Generalitat, Carmen Cabezas, said that they are studying giving a third injection to immunocompromised patients, such as transplant recipients or people undergoing cancer treatment, for example. But is a third dose really necessary to have immunity against covid?

Seven months after infection, a person retains the same level of antibodies against covid - or more. This is the main conclusion of a study by the Barcelona Institute for Global Health (ISGlobal), a centre supported by the La Caixa Foundation, in collaboration with Barcelona's Hospital Clínic. Between March and October 2020, the researchers analysed samples from 578 health professionals, measuring the level and type of antibodies (IgA, IgM or IgG) against six different covid antigens.