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Enhanced flu vaccines for people aged 65 years and over

In response to the severe 2017 influenza season, the Australian Government has funded two new enhanced influenza vaccines for people aged 65 years and over. The vaccines could boost the effectiveness of protection by about 25% compared to standard influenza vaccines, according to the authors of a Perspective published online by the Medical Journal of Australia.

Influenza is the leading vaccine-preventable cause of morbidity and mortality each year in Australia. Older people are particularly at risk of severe outcomes, such as hospitalisation, pneumonia, acute myocardial infarction and death. In 2017, 22% of all 249 932 notified influenza cases occurred in people aged 65 years and over.

The National Immunisation Program funds annual influenza vaccines for older Australians, with quadrivalent influenza vaccines (QIVs) replacing trivalent inactivated influenza vaccines (TIVs) in 2016.

However, according to the Perspective authors, led by Dr Sarah Sheridan, a public health physician at the National Centre for Immunisation Research and Surveillance, and a Research Fellow at the University of New South Wales, “the effectiveness of both the standard dose TIVs and QIVs in older people has been relatively poor, particularly against influenza A/H3N2, which consistently causes a higher proportion of disease among [people] 65 years and over as compared with other age groups”.

“Immunosenescence — broadly defined as decreased immune responses in older people — likely contributes to lower vaccine effectiveness, meaning that those most affected by influenza are also least likely to gain protection from vaccination,” Sheridan and colleagues wrote.

The two new enhanced TIVs are only registered and funded for people aged 65 years and over. They improve protection against influenza by eliciting “greater antibody responses” compared with standard TIVs. One vaccine does this by including a higher dose for each strain, whereas the other vaccine contains an adjuvant that helps boost the immune response.

“One clinical trial, in which about 16 000 participants received high dose TIV, found the relative vaccine efficacy of high dose TIV across two influenza seasons, compared with standard TIV, to be 24% against laboratory-confirmed influenza overall, including 23% better against influenza A/H3N2,” Sheridan and colleagues wrote.

“Protection against influenza-related pneumonia was enhanced by 40%.”

Although there have been no significant safety issues with the two enhanced TIVs, mild side-effects are more common for both compared with standard TIV, the authors wrote.

“Pain is the most common local reaction, occurring in 36% of high dose compared with 24% of standard TIV recipients, and 32% of adjuvanted compared with 17% of standard TIV recipients. Systemic reactions occurred in about a third of high dose and adjuvanted TIV recipients. Severe local or systemic reactions were rare (under 1%).”

They concluded that the new TIVs are likely to provide “modest additional protection against influenza which may vary from season to season”. On average, standard vaccines reduce the risk of influenza by around 40–50%.

"Theoretically, applying the relative increase in protection provided by the new TIVs, would see these enhanced TIVs have an effectiveness of around 55-63%."

Read more in Under the microscope: enhanced flu vax for elders - MJA InSight 27, 16 July 2018

The Medical Journal of Australia is a publication of the Australian Medical Association.