These Omicron sub-lineages — which have been designated BA.4 and BA.5 — were first detected in January and February in South Africa, where they have since become the dominant variants. The ECDC warned yesterday that “the presence of these variants could cause a significant overall increase in COVID-19 cases in the EU/EEA in the coming weeks and months. “The overall proportion of BA.4 and BA.5 in the EU/EEA is currently low but the high growth advantages reported suggest that these variants will become dominant.”
BA.5 infections would already seem to have begun surging in Portugal in recent weeks, accompanied by an increase in overall COVID-19 cases and test positivity rates.
In fact, as of May 8, the Portuguese National Institute of Health estimated that BA.5 already accounted for some 37 percent of all positive coronavirus cases in the country.
According to the ECDC, the estimated daily growth advantage of BA.4 over BA.2 in Portugal is 13 percent — similar to the 12 percent advantage previously recorded in South Africa.
Given this, it is estimated that BA.5 will become the dominant Omicron variant in Portugal by May 22 this year.
While data is presently somewhat limited, the ECDC noted that the two relatively new strains do not appear to result in significantly more severe infections in comparison to the BA.1 and BA.2 Omicron strains that are circulating at present.
However, they cautioned, “as in previous waves, if COVID-19 case numbers increase substantially, some level of increased hospital and ICU admissions is likely to follow”.
Given this, the ECDC is recommending that countries continue to remain vigilant for the signs of local BA.4 and BA.5 emergence.
The detection of new variants, they said, relies on sensitive and representative testing and genomic surveillance, with timely sequence reporting.
Such analyses help with the reliable estimation of the contribution of different variants to ongoing viral circulation and the impact such may have on public health outcomes.
The ECDC said: “Continued close epidemiological and vaccine effectiveness monitoring is essential in order to rapidly detect signals of increased SARS-CoV-2 circulation or risk of severe disease among vaccinated individuals.”
If such signals emerge, a second booster may be considered for some, or all, adults 60 years and older and for other vulnerable groups.
“Countries should have plans in place for the rapid deployment of booster doses in these population groups.”
A recent assessment by the ECDC found that the delivery of a second mRNA COVID-19 vaccine booster saw the clearest public health benefit when administered to those aged 80 and above — especially in situations of continuing high or increasing viral circulation.
They added: “For all age groups, it remains a priority to improve COVID-19 vaccine uptake of the primary course and first booster dose in populations who have yet to receive them.”
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According to the ECDC, the growth advantage for BA.4 and BA.5 over their predecessors that has been observed in both South Africa and Portugal stems from their ability to evade the immune protection induced by both prior Omicron infection and vaccination.
This is particularly the case where immune protection has had the opportunity to wane over time.
In fact, the experts said, preliminary studies have suggested that unvaccinated individuals who had previously been infected with BA.1 are unlikely to be protected against a symptomatic infection with both BA.4 and BA.5.
They added: “Whilst sera from vaccinated individuals performed better in invitro studies done thus far, protection derived from currently available vaccines does wane over time against the Omicron variant.”