Just how effective is the Oxford coronavirus
vaccine for the over-65s?
David
Spiegelhalter and Anthony Masters
Behind the numbers: why some European countries have
called into question the AstraZeneca jab
Sat 6 Feb
2021 19.30 GMT
While the
Medicines and Healthcare products Regulatory Agency (MHRA) and the European
Medicines Agency have both approved the Oxford-AstraZeneca vaccine for all
adults, Germany, France and six other European nations have recommended it only
for those under 65, Belgium and Italy for people under 55 and Switzerland for
nobody at all. Why are different regulators making different decisions?
The problem
is the relevant trials recruited only 660 subjects aged 65 or over: 6% of
participants. It is inevitable some groups are under-represented in studies;
the Pfizer trials included only 4% with Asian ethnicity; nobody over 89 took
part. But to have so few from those at highest risk from Covid-19 is
unfortunate, to put it mildly.
Only two
cases in this age range developed Covid-19: one among vaccinated subjects, the
other in the group who had the dummy injection. We cannot estimate efficacy
from this data alone. Many regulatory agencies concluded there was insufficient
evidence on older people, but they certainly did not suggest the vaccine was
“quasi-ineffective”, as President Emmanuel Macronthe French president asserted.
It is vital to distinguish between absence of evidence and evidence of absence.
In contrast
to saying there is no evidence for protection, the MHRA stated: “There is
nothing to suggest lack of protection.” Scientific knowledge and indirect
evidence lie behind this. First, other approved Covid-19 vaccines do not show
efficacy dropping with age. Although AstraZeneca is a viral vector vaccine,
rather than mRNA. Second, rather than repeating whole trials on groups who did
not take part in clinical trials, say of different ethnicities, researchers use
“bridging studies” that compare biological responses. For the AstraZeneca
vaccine, there were similar levels of neutralising antibodies across age. It is
reasonable to assume protection in older people will be like that in younger
adults.
These are
not normal circumstances, so the calculus of caution changes. There are nearly
2,500 reported Covid-19 daily deaths across the European countries that have
restricted the vaccine. Direct evidence on older people will be coming from a
US study, which could change future decisions. But in the meantime, unless
there are ample alternatives, regulatory choices may delay protecting the most
vulnerable and so cost lives.
• David
Spiegelhalter is chair of the Winton Centre for Risk and Evidence Communication
at Cambridge. Anthony Masters is statistical ambassador for the Royal
Statistical Society
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