Over nine thousand doses of flu vaccine - varying between three different brand names - were distributed at Altnagelvin over the past three years, the Sentinel can reveal.
And whilst 500 doses of the swine flu vaccine Pandemrix - linked to an unexpected spike in juvenile narcolepsy cases in Europe - were purchased in 2011, when the Chief Medical Officer said there had been no plans to use it, they were never dispensed.
The Western Trust has provided the Sentinel with details of vaccine dispensation from 2011 onwards.
The Sentinel previously revealed how 8,690 doses of Pandemrix were dispensed at the Londonderry Hospital whilst a total of 12,780 doses were dispensed across Altnagelvin, the Erne Hospital and the Tyrone County Hospital over 2009 and 2010.
New figures show that between 2011 and 2013, 9,527 flu vaccines were issued at Altnagelvin, whilst 14,080 were dispensed across the three hospitals together over the same period.
The favoured brands at Altnagelvin over the period included Enzira, Sanofi Pasteur and Fluenz.
And although the Public Health Agency (PHA) told the Sentinel in 2011, there were no plans to use Pandemrix that year, 50 10 dose vials of the drug were purchased. None of these were used, however.
In 2011, 3,667 doses of Enzira were issued at Altnagelvin; in 2012, 2,010 doses of Sanofi Pasteur were issued at the hospital; and in 2013, 1,990 doses of Sanofi Pasteur and 1,860 doses of Fluenz were preferred.
The Pandemrix vaccine was produced specifically to protect against swine flu in the year of the 2009 H1N1 swine flu pandemic. Concerns over the drug were first raised back in August 2010 when Sweden reported an unexpected increase of cases of juvenile narcolepsy following immunisation with Pandemrix. Finland subsequently suspended the use of the vaccine as a similar spike was seen in that country.
Last month the Sentinel reported how the H1N1 flu, which circulated amongst humans for the first time in 2009, is now the main virus affecting people here.