Omicron subtype has apparent transmission advantage
UKHSA said that there was an increased growth
rate of BA.2 compared with BA.1 in all regions of England where there were
enough cases to compare them, and that “the apparent growth advantage is
“We now know that BA.2 has an increased
growth rate which can be seen in all regions in England,” said Dr Susan
Hopkins, Chief Medical Advisor for the UKHSA.
The agency said there was no data on the
severity of BA.2 compared to BA.1, but reiterated that a preliminary assessment
did not find a difference in vaccine effectiveness against symptomatic disease
between the two omicron subtypes.
The rapid spread of BA.1 fuelled an omicron
wave which pushed cases to record highs in Britain in December, displacing the
previously dominant delta variant.
However, hospitalisations did not rise to the
same extent, owing to population immunity through vaccination and previous
infection, as well as omicron’s lower severity.
The UKHSA said that a separate analysis showed
that between Nov 24 and Jan 19, the majority of intensive care admissions from
COVID-19 had delta infections, even as omicron was growing to dominate the
number of cases.
It also found that a rise of cases of omicron
in care homes had not been associated with an increase in hospital admissions.
“Our findings suggest the current wave of
omicron infections is unlikely to lead to a major surge in severe disease in
care home populations with high levels of vaccine coverage and/or natural
immunity,” UKHSA said, noting that the findings were based on BA.1 due to
limited numbers of BA.2 cases in the study.