By Alexander Winning
JOHANNESBURG, Dec 9 (Reuters) - Efficacy results may not be
ready for months from a trial of AstraZeneca and Oxford
University's coronavirus vaccine in South Africa, the principal
investigator of the South African study told Reuters.
AstraZeneca published findings this week from trials
in Brazil and Britain showing its vaccine was on average about
70% effective in preventing coronavirus infection. It is seeking
regulatory approval in several countries for its shot.
However, the company has faced calls to provide more data,
after it found that the efficacy was higher in a small sub-group
of participants given a smaller initial dose.
A larger U.S. trial has been delayed, potentially slowing
down approval there of what has long been seen as one of the
leading vaccine candidates. The published findings also did not
include efficacy data from South Africa, where around 2,000
people are participating in a trial.
Shabir Madhi, professor of vaccinology at the University of
the Witwatersrand, said too few participants in South Africa had
contracted the coronavirus at the right time -- at least two
weeks after receiving two doses of either the vaccine or a
placebo control -- to analyse the data.
In order to demonstrate 60% efficacy, about 46 trial
participants needed to test positive, he said. As of early last
month fewer than five had tested positive more than two weeks
after the second dose, known as an "endpoint case".
"Right now we are still somewhat thin in terms of the number
of endpoint cases to do an analysis for an efficacy readout. In
all likelihood we would require another resurgence, which is
currently in the making in South Africa, before we would accrue
an adequate number of endpoint cases," Madhi said.
Coronavirus cases had been surging in South Africa rapidly
when the study was launched in June, and a number of
participants ended up testing positive too early to say whether
the vaccine might have protected them. Cases then dropped off at
the time when they would have produced helpful data.
Moderna and Pfizer were able to analyse
their rival vaccine candidates so quickly because most of the
vaccination took place before infections surged, so when the
surge happened endpoint cases accrued swiftly, Madhi added.
"The time to be enrolling to these studies is not when the
peak is upon you, but a good few months before that," he said.
AstraZeneca-Oxford's interim analysis of its British and
Brazilian trial data was based on a total of 131 COVID-19 cases.
Pfizer and Moderna analysed their data after just over 90
infections.
Madhi estimated his study could reach the required number of
endpoint cases around February or March next year. In July he
had expressed hope that researchers would be able to analyse
efficacy by the end of November.
(Reporting by Alexander Winning
Additional reporting by Kate Kelland
Editing by Josephine Mason and Peter Graff)