Introduction: “The coverage of SARS-CoV-2 vaccination in large parts of the world, together with the high number of breakthrough infections, especially following the emergence of Omicron subvariants, makes hybrid immunity (resulting from vaccine and infection) common. Hybrid immunity, particularly after BA.1 or BA.2 infection, confers substantial protection against the BA.5 infection.1, 2, 3 However, although the waning of protection afforded by natural infection in non-vaccinated individuals or by vaccination has been well documented,4, 5 the stability of hybrid immunity, specifically against the BA.5 subvariant, now dominant in many countries, has not been thoroughly addressed.

We used the Portuguese COVID-19 registry (SINAVE), which includes all notified cases of infection in the country on the basis of an official positive test and irrespective of clinical presentation, to investigate the risk of reinfection with BA.5 in a highly vaccinated population previously infected with BA.1 or BA.2 subvariants. We included the population aged 12 years or older, for whom the vaccination coverage was greater than 98% at the end of 2021 (appendix pp 4–5). The registry is very comprehensive due to legal requirements for compensation payment during mandatory isolation. We include infection data from the start of the pandemic until Sept 14, 2022. …”

Malato J, Ribeiro RM, Fernandes E, Leite PP, Casaca P, Antunes C, Fonseca VR, Gomes MC, Graca L. Stability of hybrid versus vaccine immunity against BA.5 infection over 8 months. Lancet Infect Dis. 2023 Feb;23(2):148-150. doi: 10.1016/S1473-3099(22)00833-7. Epub 2023 Jan 5. PMID: 36620968; PMCID: PMC9815828.

https://pubmed.ncbi.nlm.nih.gov/36620968/?dopt=Abstract