influenza vaccine
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A recent study described the ability of low-efficacy flu vaccines to prevent infection and determine who should be vaccinated to decrease hospitalizations.

Influenza, more commonly known as the flu, is a disease caused by the influenza virus. As a highly prevalent virus, flu infections greatly impact the health of many individuals across the world. Infections can result in moderate symptoms such as fevers and coughs but can progress to life-threatening conditions, especially in young children and the elderly. These populations are at the most risk because their immune systems are not as robust as those in youth and younger adults.

Influenza viruses constantly change

Influenza viruses rapidly evolve, which is why scientists have not been able to use just one vaccine to combat the flu. Each season, scientists are required to make a new formula of the vaccine.

Since the mass production of influenza vaccines takes time and influenza viruses are constantly evolving, there is the potential for vaccines to be less effective than normal, resulting in higher infection rates. Moreover, media coverage of the reduced vaccine efficacy may further depress uptake.

Although flu vaccines may not always be the most effective, public health experts still recommend people to get the vaccine. A group at the Yale School of Public Health sought to investigate the extent that low-efficacy influenza vaccines can help prevent infections on a population scale and recently published their findings in the Proceedings of the National Academy of Sciences.

Mathematical modelling of influenza infections

The researchers used mathematical modelling to study the dynamics of influenza transmission and to determine the effectiveness of vaccination programs. The researchers used optimization algorithms to investigate the best uptake of low-efficacy flu vaccines in the American population among different age groups. The outcomes of the study focused on minimizing incidence, hospitalizations, deaths, and overall burden of the disease.

Flu vaccines prevent infections and death

Over the past five years, the average flu vaccine uptake rate is at 43%, which does not cover half the population. However, the predicted effect of this coverage still prevents 77 million infections and 130,000 deaths each season in the United States. With a 43% uptake rate of a low-efficacy flu vaccine that only protects 20% of vaccinated individuals, the mathematical model predicted that 21 million infections and 62,000 deaths would be avoided, compared to no vaccinations.

Of note, this group determined that increasing the vaccination coverage by 7% to 50% could prevent another 8,500 deaths. The prediction model also highlights the fact that vaccine coverage plays a more important role than vaccine efficacy in positive health outcomes.

Optimizing the distribution of influenza vaccinations

The study looked at optimizing the distribution of low-efficacy influenza vaccinations using complex algorithms, which predicted the prevention of almost twice the number of influenza infections if optimized.

Prioritizing vaccination of children or youth (5 to 19 years of age) and young adults (30 to 39 years of age) would prevent the most infections since these groups are the primary contributors to transmission of influenza. The mathematical models in this study also predicted that as the efficacy of flu vaccines decreases, it becomes more important to vaccinate the elderly over young adults.

Study outlines clear strategies for administering flu vaccines depending on the flu season

The data presented in this study is extremely novel and relevant to an important and recurring public health issue. As described above, this study outlines clear strategies that shift depending on the efficacy of the annual influenza vaccine. Their prediction model can therefore be applied after determining the efficacy of the seasonal flu vaccine, guiding crucial health policy and outreach efforts to maximize vaccination coverage and decrease influenza burden over one flu season.

As a universal flu vaccine is still out of reach and under development, it remains of utmost importance that public health institutions find the best way to administer annual vaccines, which vary in efficacy, in order to minimize influenza burden in a population.

Written by Branson Chen, BHSc

Reference: Sah P, Medlock J, Fitzpatrick MC, Singer BH, Galvani AP. Optimizing the impact of low-efficacy influenza vaccines. Proceedings of the National Academy of Sciences. 2018 Apr 25:201802479.

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