Available data from individuals who have experienced prior BA.1 infection show that both BA.4 and BA.5 are able to escape immune protection induced by infection with BA.1. As such, individuals who are vaccinated (or who are unvaccinated) are unlikely to be protected against symptomatic infection with BA.4 or BA.5. In general, BA.4 and BA.5 lineages have the ability to evade immune responses, but vaccination is still effective against severe disease in most cases. Moreover, although sera from vaccinated individuals performed better in in vitro studies to date, protection derived from currently available vaccines does wane over time against Omicron variants, per the ECDC.
As of May 12, 2022, the ECDC has reclassified Omicron variants BA.4 and BA.5 from variants of interest to variants of concern.
Although data are still emerging, preliminary studies suggest a significant change in antigenic properties of BA.4 and BA.5 compared with BA.1 and BA.2. Serum from those who had received three doses of either the AstraZeneca or the Pfizer vaccines showed reduced neutralization of BA.4 and BA.5 compared with BA.1 and BA.2. In those with breakthrough BA.1 infections, sera revealed significant reductions in the neutralization of BA.4 or BA.5, suggesting that repeat infections are possible in vaccinated individuals. According to current data, persons with one dose of vaccination had the highest reinfection rate, at 642.2 per 100,000, followed by unvaccinated persons (536.2 per 100,000) and two-dose vaccinated persons (406.3 per 100,000).
Learn more about BA.4 and BA.5.
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Cite this: Glenn Wortmann. Fast Five Quiz: COVID-19 Variants - Medscape - Aug 03, 2022.