Lopez MJ, Vazquez MM, Alvarez M et al.  

Phase IIb HIPRA-HH-2 study results showed that PHH-1V as first booster dose elicited a strong and sustained neutralising antibody response against various SARS-CoV-2 variants. Here, we report the safety and immunogenicity of a fourth booster dose of PHH-1V against the most prevalent Omicron SARS-CoV-2 variants in Spain.