Hat tip Sharon Sanders
https://flutrackers.com/forum/forum/...nt-fourth-wave
The Lancet
Clinical severity of COVID-19 patients admitted to hospitals in Gauteng, South Africa
during the Omicron-dominant fourth wave
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The reasons for the lower admission rates and less severe infections in admitted patients during the
Omicron-dominated fourth wave are not known but are likely to be due to a less virulent virus, and high
immunity from prior infection(s) or vaccination, especially the large numbers of vaccinated individuals
who had prior infection and so have “hybrid immunity” (14). A tissue-based study showed that Omicron
infects the cells of the bronchus faster but cells of the lung slower than Delta (15); which may at least
partially account for the less severe infections observed in the Omicron-dominated wave.
Immunity stemming from prior infection has provided protection against symptomatic infection with
previous variants (16) however preliminary data from South Africa (17) suggest that reinfections with
Omicron are high. While prior infection may not prevent symptomatic breakthrough infection, it may
generate T-cell responses that provide protection from severe disease (18), thereby contributing, at
least partially to the observed high infection rate but low severity due to Omicron. The province of
Gauteng experienced a particularly severe wave of Delta infection leading to a large increase in
seroprevalence following the Delta-driven third wave. If prior infection with the Delta variant specifically
provides some T-cell immunity that protects against severe disease from Omicron infection, this could
be a contributor to the less severe Omicron infections observed in the Omicron-driven fourth wave.
While SARS-CoV-2 vaccine effectiveness in preventing symptomatic infection has been impacted by
the emergence of variants (19), vaccination has reduced the risk of severe disease from past variants
(20). Since vaccination coverage in Gauteng is higher in individuals aged above 60 years, it may have
made an important contribution to the lower severity of Omicron infections, especially in the elderly. But
vaccination cannot fully account for the markedly lower numbers of severe infections in 20-39 year-old
individuals, as less than a third of this age group was vaccinated. One of the two vaccines being rolled
out in South Africa is the Ad26.CoV2.S vaccine which generates lower antibody but better T-cell
responses (21). The role of this specific vaccine in reducing disease severity but not clinical infections
needs to be assessed.
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