Influenza Vaccine Safety & Effectiveness
Recent analysis of pooled research showed that the chance of benefiting from influenza vaccination is not as great as might be expected for healthy adults: at least 40 people would need vaccination to avoid one case of an “influenza like illness”, and 71 people would need vaccination to prevent an actual case of influenza. Vaccinated adults did no better when measured in terms of sick days taken or more seriously, in the need for hospitalisation. The full article is available at the Cochrane Library website (if logging in from an Australian location); refer to the ‘Plain Language Statement’ if seeking a simplified summary.
The term “influenza like illness” refers to an illness with similar symptoms to actual influenza but which may or may not be caused be the influenza virus. From a symptomatic viewpoint, without laboratory testing it is often difficult to distinguish between the two. The emphasis here however is on the effect of the influenza vaccine on healthy adults, who arguably are the predominant group in receipt of the influenza vaccine. Explaining these figures, the research indicates that 1 in 40 of healthy adults who are vaccinated will escape the symptoms of an ‘influenza like illness’. To use an example, consider two groups each of 80 people, both randomly sampled at the end of the flu season from the general population, and separated into those that have and those that have not, had the influenza vaccine. If at the end of the flu season 5 people had experienced an ‘influenza like illness’ in the unvaccinated group, one would expect 2 less cases of an ‘influenza like illness’ (ie 80 divided by 40) in the vaccinated group. Similarly, if there were 5 case of actual influenza in the unvaccinated group, one would expect 4 cases (approximately) in the vaccinated group. In closed groups, such as workplace situations, the protection rate could be much higher as we are not referring to randomly sampled situations.
Obviously, statistics alone should not be the sole reason in deciding whether to vaccinate or not. Certain groups of adults and children have been identified as being at increased risk, to the extent that the vaccine is provided free to GP clinics for those in such groups. The list is at available at the Dept. of Health, Victorian Government, viz:
- People who are 65 years of age and over
- Pregnant women at any time during their pregnancy
- Aboriginal and Torres Strait Islander people aged 15 years and older
- Residents of nursing homes and other long-term care facilities
- Any person 6 months of age and older with a chronic condition predisposing to severe influenza illness that requires regular medical follow-up or hospitalisation, including children aged 6 months to 10 years undergoing long-term aspirin therapy, and people with:
- cardiac disease
- chronic respiratory conditions
- immunocompromising conditions
- renal disease
- diabetes and other metabolic disorders
- chronic neurological conditions
- haematological disorders
- Down syndrome and fall under one of the above categories
- obesity (BMI greater than or equal to 30 kg/m2) and fall under one of the above categories
- alcoholism requiring regular medical follow-up or hospitalisation in the preceding year and fall under one of the above categories.
Note that healthy children are not included in the above, although the benefit of influenza vaccine seems greater for children, as reported in a separate Cochrane review, with one in eight being protected from ‘influenza like illness’ and one in twenty eight protected from actual influenza. However, the researchers found no evidence that immunisation decreased the rate of secondary cases (ie as spread to contacts), lower respiratory tract disease (such as influenza pneumonia), the need for prescribed medication, middle ear infection and impact of a socioeconomic nature.
However the research reports no benefit in children under six with the ‘inactivated’ vaccines in use in Australia and raises concerns about the lack of good research into flu vaccine safety. This is particularly relevant given the reporting of over 1700 reactions to influenza vaccine in 2010 over in Western Australia. This resulted in the authorities withdrawing approval for a particular brand of the vaccine to children under 5 years of age (the CSL based ‘Fluvax’ brand). This withdrawal remains in place as at 2014. Refer to the TGA report Investigation into febrile reactions in young children for more information.
Another concern raised by the authors related to the sources of studies included in their review. Although not confirmed in their current review, reference was made to studies provided by the pharmaceutical industry for a previous review in 2007. The authors reported the industry studies seemed to have more favourable outcomes, and appeared in the more prestigious journals with more citations, than those provided by independent or Government sources, irrespective of their quality or size. Somewhat damningly, the authors concluded that “reliable evidence on influenza vaccines is thin but there is evidence of widespread manipulation of conclusions and spurious notoriety of the studies. The content and conclusions of this review should be interpreted in the light of this finding”.