COVID-19 vaccines: is a second booster necessary at this moment, and for whom?

Circulation of the Omicron BA.5 subvariant has led to a considerable increase in cases and also in hospitalisations (but not severe cases or deaths) in recent weeks in Catalonia, the rest of Spain and many other countries. This, coupled with the fact that antibody levels after a first booster dose - offered late last year and early this year - have been declining, raises the question: is a second booster dose necessary at this moment? And if so, for whom?

Based on scientific evidence and the current epidemiological situation, the Multidisciplinary Collaborative Group for the Scientific Monitoring of COVID-19 (GCMSC) has conducted an analysis of the impact of the BA-5 subvariant in Catalonia and, with the support of the COVID-19 Scientific Advisory Committee (CCAC) attached to the Department of Health of the Government of Catalonia, has issued a new report with a series of recommendations for booster vaccination strategies. 

The experts start by stressing that, although the effectiveness of vaccines against infection has declined considerably since the spread of Omicron and its subvariants, protection against severe disease and death remains high. They also point out that a large percentage of the population in Catalonia has been infected with Omicron and that this hybrid immunity (vaccination plus infection) increases protection against severe disease.

They consider that, given the high circulation of BA.5 in Catalonia, and the fact that the vast majority of people hospitalised with COVID-19 are elderly, it is necessary to administer a fourth dose to people aged 80 years and older, as well as to people in nursing homes. However, they do not recommend a second booster (or fourth dose) for the rest of the population, as the benefit is limited and a high proportion of people have been recently infected.

"A few days ago, the ECDC recommended administering a second booster in people over 60. But given that in Catalonia the incidence is already starting to fall, we think it is better to wait and administer booster doses in view of future waves, for example, this autumn," says Julià Blanco, IGTP researcher and group leader at IrsiCaixa, as well as lead author of the report. 

The evolution of the virus and the epidemiological situation will determine the need to administer a second booster to the general population, as well as whether to use a vaccine adapted to the new variants. The evidence to date suggests that variant-adapted vaccines do not provide much benefit compared to the original vaccine, although Moderna recently announced that its bivalent vaccine (with original Spike and Spike of BA.1) induces a good level of neutralising antibodies even against BA.4 and BA.5.

Finally, the group points out the importance of a good communication strategy to achieve a high coverage of booster doses in the different target populations.

About the Multidisciplinary Collaborative Group for the Scientific Monitoring of COVID-19 (GCMSC)

The GCMSC is a group promoted by the Barcelona Institute for Global Health (ISGlobal), a centre promoted by the "la Caixa" Foundation, and the Official College of Doctors of Barcelona (CoMB), with the support of the Catalan Association of Research Centres (ACER).

The authors of the analysis document are Julià Blanco, Adelaida Sarukhan, Juana Díez, Quique Bassat, Magda Campins, Robert Güerri, Carles Brotons, Mireia Sans, Josep M Miró, Silvia de Sanjosé, with additional support from Antoni Plasència and Josep M. Antó.