Title : Adapted mRNA COVID-19 vaccines have a limited ability to establish herd immunity in the population against Omicron BA.1 and BA4-5 variants of SARS-CoV-2
Abstract:
The emergence of novel SARS-CoV-2 variants has raised concerns about the ability of COVID-19 vaccination programs to establish adequate herd immunity levels in the population. Adapted mRNA COVID-19 vaccines against BA.1 and BA.4-5 Omicron variants can provide a greater immunity against emergent SARS-CoV-2 variants than vaccines against the original variant. This study assessed the effectiveness of adapted vaccines in preventing SARS-CoV-2 infection and the ability of the adapted vaccines to establish herd immunity against emerging Omicron variants. Firstly, a systematic literature review was conducted to estimate the absolute vaccine effectiveness (aVE) in preventing SARS-CoV-2 infection using adapted vaccines targeting Omicron variants. Secondly, the ability of the adapted vaccines to establish herd immunity was assessed by taking into account the following factors: aVE, Ro values of SARS-CoV-2, and the use of non-pharmacological interventions (NPIs). The study found a meta-analysis based aVE in preventing severe disease and SARS-CoV-2 infection of 56−60% and 36−39%, respectively.
Nevertheless, the study found that the ability to block SARS-CoV-2 transmission was limited because they could not block the transmission of viruses with greater transmissibility. Firstly, the adapted vaccines could not establish herd immunity against the Omicron BA.1 and BA.4-5 variants without using non-pharmacological interventions (NPIs). Secondly, the adapted vaccines could establish herd immunity only by achieving >80% vaccination coverage, using NPIs with greater effectiveness and when a 20−30% percentage of individuals were already protected against SARS-CoV-2 in the population. New adapted COVID-19 vaccines with greater effectiveness in preventing SARS-CoV-2 infection must be developed to increase herd immunity levels against emerging SARS-CoV-2 variants in the population and reduce the health impact of emerging SARS-CoV-2 variants.
