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While the exact reason for the drop is unknown, international experts' recent criticism of the vaccine's efficacy certainly isn't helping.
In October 2006, Health24 reported on the findings of Dr Tom Jefferson, co-ordinator of the Cochrane Vaccines Field in Rome, Italy. His research lead him to conclude that influenza vaccines have little or no effect on many influenza campaign objectives, such as reducing hospital stay, time off work and death from influenza and its complications.
Jefferson looked at all the systematic reviews that he could find on the effects of inactivated influenza vaccines. In other words, he looked at published papers that did not generate new data but analysed existing studies.
His conclusion – as well as that of a few other reviewers – was that there is an exaggerated expectation of what influenza vaccines actually do.
Reviewers made 'serious errors'
But Dr David Fedson, an international authority on adult immunisation and co-ordinator of the Macroepidemiology of Influenza Vaccination (MIV) Study Group, disagrees: "These reviewers and independent investigators have made serious errors in their analysis and interpretation of the findings."
In systematic reviews, such as the one Jefferson did, errors slip in when the results of observational, retrospective studies are dismissed and the focus is placed solely on randomised, prospective studies, Fedson told Health24.com.
A prospective study is designed ahead of time. This means that study participants are selected, randomly assigned to groups, and examined according to the design of the experiment. In a retrospective study, known outcomes are examined in hindsight, using existing records.
In the case of flu vaccination, a prospective study would, for example, look at the development of complications in two groups of individuals: one group that received a flu shot and another group of people that didn't. The different outcomes would then be measured.
On the other hand, a retrospective study could, for example, investigate the number of vaccinated people who were hospitalised due to pneumonia or other flu-related complications during a recent flu season.
Retrospective studies valid
Fedson explains that the retrospective study approach is frequently used by epidemiologists. As an example, he refers to the observational studies done by Charles Darwin and points to the fact that Darwin's theories on evolution are widely accepted and entirely valid.
In the same way, Fedson says, data from retrospective studies on the efficacy of flu vaccines are indeed valuable – and change the picture entirely, showing that the vaccine does indeed reduce influenza-related complications, hospital admissions etc.
"There are many different ways in which to reach the truth," Fedson says. "Unfortunately, reviewers often come to very stark conclusions."
How the flu vaccine works
Experts believe that the influenza vaccine is still the most important way to either avoid influenza altogether, or to reduce its severity.
Vaccines commonly used are produced from a killed virus. Most vaccines are made from highly purified, egg-grown viruses that have been made non-infectious.
The flu vaccine is effective for eight to 12 months. This is one reason why it has to be repeated every year. The other is because of the changing flu strains.
Concern about South Africa
Fedson is concerned about the fact that fewer South Africans are receiving their annual flu shots than before. "There is a considerable amount of wealth in this country that can be channelled towards flu prevention," he says.
One could argue that the country has more important health concerns, such as HIV/Aids. But, Fedson says, flu vaccination can play an important role in the lives of people living with HIV/Aids. Patients who aren't profoundly immuno-compromised respond well to the vaccine.
"As many people with HIV/Aids have a shorter life expectancy, physicians need to ensure that the patients' final years are as good as they can be," Fedson says. "The flu vaccine can help to achieve this." – (Carine van Rooyen, Health24)
