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The current monovalent mRNA COVID-19 vaccines show varying effectiveness against the BA.5 variant, with waning protection over time. Vaccine effectiveness (VE) against COVID-19-associated hospitalization during the BA.4/BA.5 predominant period was observed to be 83% within 14-150 days after the second dose, decreasing to 37% after 150 days. VE was 60% within 7-120 days after the third dose, decreasing to 29% after 120 days, and 61% within 7-120 days after the fourth dose.[1]
Neutralization studies have shown that the BA.5 bivalent booster elicits high neutralizing titers against BA.4/5 but does not produce robust neutralization against newly emerged BA.2.75.2, BQ.1.1, or XBB.1.[2] The Omicron BA.5 variant has been found to significantly escape neutralizing antibodies from a range of vaccination and convalescent responses.[3] Additionally, BA.4/5 shows reduced neutralization by serum from individuals vaccinated with triple doses of AstraZeneca or Pfizer vaccines compared to BA.1 and BA.2.[4]
In summary, the current COVID-19 vaccines provide some protection against the BA.5 variant, but the effectiveness wanes over time and is reduced compared to earlier variants. Bivalent mRNA COVID-19 vaccines are expected to offer better protection against BA.4/BA.5.[1]


2.Kurhade C, Zou J, Xia H, et al. Low Neutralization of SARS-CoV-2 Omicron BA.2.75.2, BQ.1.1 and XBB.1 by Parental mRNA Vaccine or a BA.5 Bivalent Booster. Nature Medicine. 2023;29(2):344-347. doi:10.1038/s41591-022-02162-x.
3.Aggarwal A, Akerman A, Milogiannakis V, et al. SARS-CoV-2 Omicron BA.5: Evolving Tropism and Evasion of Potent Humoral Responses and Resistance to Clinical Immunotherapeutics Relative to Viral Variants of Concern. EBioMedicine. 2022;84:104270. doi:10.1016/j.ebiom.2022.104270.
4.Tuekprakhon A, Nutalai R, Dijokaite-Guraliuc A, et al. Antibody Escape of SARS-CoV-2 Omicron BA.4 and BA.5 From Vaccine and BA.1 Serum. Cell. 2022;185(14):2422-2433.e13. doi:10.1016/j.cell.2022.06.005.