High-Dose Vaccine May Reduce Deaths During Severe Flu Season

Nicola M. Parry, DVM

March 03, 2017

Among older adults, the high-dose influenza vaccine appears to be more effective than the standard-dose vaccine at preventing influenza-related deaths in seniors during a more severe influenza season, a new study shows.

David K. Shay, MD, from the Centers for Disease Control and Prevention, Atlanta, Georgia, and colleagues published the results of their study online March 2 in the Journal of Infectious Diseases.

"[W]e found a significant reduction of approximately 35% in post-influenza deaths associated with receipt of high-dose vs standard-dose vaccines in 2012–2013, but not in 2013–2014," the authors write.

Seniors who receive high-dose influenza vaccines have fewer influenza-related outcomes, including office visits and hospitalizations. However, whether these vaccines reduce the risk for influenza-related death has been unclear, especially because the low risk for death among these patients makes trials to assess this endpoint unfeasible.

Dr Shay and colleagues therefore performed an observational study to compare the effectiveness of high-dose vs standard-dose influenza vaccine in preventing influenza-related deaths during the 2012 to 2013 and 2013 to 2014 influenza seasons, when influenza viruses and vaccines were similar.

Using the Centers for Medicare & Medicaid Services databases, the researchers analyzed data on Medicare beneficiaries aged 65 years or older who received either the high-dose or standard-dose influenza vaccine during the 2012 to 2013 and 2013 to 2014 influenza seasons from community-located pharmacies. They studied 1,039,645 recipients of high-dose and 1,683,264 recipients of standard-dose influenza vaccines during the 2012 to 2013 season, and 1,508,176 high-dose and 1,877,327 standard-dose recipients during the 2013 to 2014 season.

The authors note that during the 2012 to 2013 season, H3N2 influenza viruses (known to cause higher mortality in seniors) predominated, but during the 2014 to 2014 season, H1N1 influenza viruses predominated.

Comparative vaccine effectiveness (VE) was 24.0% (95% confidence interval [CI], 0.6% - 42%; P = .12), the authors write.

They found that, during the 2012 to 2013 season, when H3N2 viruses predominated, people who received a high-dose vaccine were 36.4% (95% CI, 9.0% - 55.6%) less likely to die within 30 days of either an influenza hospitalization or emergency department visit than people who received the standard-dose vaccine.

This reduction in mortality was also "accompanied by significant decreases of approximately 20% in influenza-related visits and hospital-based influenza diagnoses," the authors add.

However, during the 2013 to 2014 season, when H1N1 viruses predominated, the high-dose vaccine was not significantly better than the standard-dose vaccine at preventing deaths among the patients (2.5%; 95% CI, −46.8% to 35.3%). This reduced effectiveness compared with 2012 to 2013 could be because of several reasons, the authors note. These include differences in the people who received high-dose vaccine, in the circulation patterns of specific influenza viruses, and in the antigenic relatedness of vaccine and wild-type viruses.

Overall, these findings suggest high-dose influenza vaccines may be most beneficial during seasons when H3N2 influenza viruses circulate most commonly, stressing the need for influenza vaccines that offer better protection against these viruses.

"The availability of A(H3N2) vaccines offering substantially better protection for older adults and their widespread use in this population could lead to meaningful reductions in influenza-associated morbidity and mortality," Dr Shay and colleagues conclude.

In an accompanying editorial Arnold S. Monto, MD, from the University of Michigan School of Public Health, Ann Arbor, highlights data from another study in which vaccine efficiency of standard vaccine in all age groups in the 2013 to 2014 season was approximately 54% compared with only 39% in 2012 to 2013.

Dr Monto also notes that the findings of the study by Dr Shay and colleagues are consistent with those from previous studies showing that the high-dose influenza vaccine more effectively protects people against uncomplicated illness, and probably hospitalizations.

"This indicates that improvement in our 70-year-old influenza vaccines is possible, and to get there more quickly we should not ignore older technologies while working on more dramatic advances," writes Dr Monto.

Although advances in influenza vaccine development, including the high-dose vaccine and adjuvanted vaccines, provide effective countermeasures against infection, Dr Monto says these should be considered just the beginning of programs that aim to further improve influenza vaccine technologies.

"The biggest payoff of better vaccines in terms of reduced mortality will be in the elderly, but much of the vaccine in the United States is used at younger ages, and improvement, especially of A(H3N2) vaccines, is needed for all age groups," he concludes.

This study was funded by the Centers for Disease Control and Prevention and the US Food and Drug Administration, and was performed as a joint initiative of the Centers for Medicare & Medicaid Services, the US Food and Drug Administration, and the Centers for Disease Control and Prevention. One author has reported receiving limited travel support to meetings unrelated to this study from Sanofi Pasteur. The remaining authors have disclosed no relevant financial relationships. Dr Monto has reported receiving grants and personal fees from Sanofi Pasteur, and personal fees from Novartis, all of which are unrelated to this study.

J Infect Dis. Published online March 2, 2017. Article full text, Editorial full text

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