Rates of BA.4 and BA.5 remain low in Europe despite recent increase in prevalence
According to the European Centre for Disease Prevention and Control (ECDC), most European Union/European Economic Area (EU/EEA) countries have detected low proportions of the SARS-CoV-2 variants BA.4 and BA.5, however many have seen an increase in recent weeks.
In Portugal, BA.5 has become the dominant SARS-CoV-2 variant and the increasing proportions of BA.5 have been accompanied by a surge in COVID-19 cases. The growth advantage reported for BA.4 and BA.5 suggest that these variants will become dominant throughout the EU/EEA, probably resulting in an increase in COVID-19 cases in coming weeks.
The extent of the increase in COVID-19 cases will depend on various factors, including immune protection against infection influenced by the timing and coverage of COVID-19 vaccination regimes, and the extent, timing and variant landscape of previous SARS-CoV-2 pandemic waves. Based on limited data, there is no evidence of BA.4 and BA.5 being associated with increased infection severity compared to the circulating variants BA.1 and BA.2. However, as in previous waves, an increase in COVID-19 cases overall can result in an increase in hospitalizations, ICU admissions and deaths.
Countries should remain vigilant for signals of BA.4 and BA.5 emergence and spread; maintain sensitive and representative testing and genomic surveillance with timely sequence reporting, and strengthen sentinel surveillance systems (primary care ILI/ARI and SARI). Countries should continue to monitor COVID-19 case rates - especially in people aged 65 and older - and severity indicators such as hospitalizations, ICU admissions, ICU occupancy and death.
Improving COVID-19 vaccine uptake of the primary course and first booster dose in populations who are yet to receive them remains a priority. It is expected that additional booster doses will be needed for those groups most at risk of severe disease, in anticipation of future waves.
Event background
The SARS-CoV-2 variants BA.4 and BA.5 were first detected in South Africa in January and February 2022, respectively. They became the dominant variants in that country in May 2022 and a parallel increasing trend in epidemiological indicators, such as case notification rates and test positivity rates, suggested that these two variants were responsible for the surge in cases observed in South Africa in April−May 2022. As of 12 May 2022, ECDC reclassified Omicron sub-lineages BA.4 and BA.5 from variants of interest to variants of concern.
BA.4 and BA.5 are two sub-lineages of the Omicron clade (B.1.1.529). They share the same mutation profile in the spike gene, while they have different sets of mutations in their remaining genome. The defining mutations in the spike protein of BA.4 and BA.5 compared to BA.2 include Δ69-70, L452R, F486V and R493Q (reversion). Given the current epidemiological background where BA.2 is the dominant variant in the EU/EEA, laboratories can use the presence of the spike changes L452R or F486V or S-gene target failure as a pre-screening for the variants. To be able to differentiate between BA.4 and BA.5, assays targeting discordant parts outside of the spike gene or whole genome sequencing (WGS) are required. Since BA.4 and BA.5 only emerged recently, it has not yet been possible to include the variants in a rapid antigen detection test (RADT) evaluation study.
There is currently no indication of any change in severity for BA.4 or BA.5 compared to previous Omicron lineages. Severity indicators in Portugal (hospitalization, ICU admissions and deaths) as of June 1 are below the levels reached in the previous Omicron peak, however, week-on-week increases continue to be observed. Over the past six weeks, both hospitalizations and ICU admission increases have mainly been among those aged 60 years and above.
