Antibodies Predict Effectiveness of Flu Vaccine

The titers of 2 antibodies that protect against hemagglutination and neuraminidase can predict the effectiveness of the flu vaccine, new research suggests.

In an effort to improve the effectiveness of the flu vaccine worldwide, the researchers aimed to determine whether hemagglutination inhibition (HAI) titers affect the likelihood of developing mild to moderate influenza disease.
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To conduct their study, the researchers recruited 65 healthy volunteers aged 18 to 50 years to receive a wild-type A 2009 A (H1N1) influenza A challenge virus at the National Institutes of Health Clinical Center in Bethesda, Maryland.

At baseline, the researchers measured volunteers’ HAI and neuraminidase inhibition (NAI) titers and separated them into 2 groups: those with HAI titers of 1:40 or lower and those with HAI titers of more than 1:40. They then introduced the flu virus via intranasal dose.

After 9 days of quarantine in the clinic and constant monitoring, volunteers were discharged if they had not contracted the flu. They were also required to follow up with the researchers 4 times over the following 2 months.

Results showed that volunteers with high HAI titers at baseline were less likely to get mild to moderate influenza disease and had some reduction in duration compared with those with low HAI titers. However, they were just as likely to report flu symptoms as those with low HAI titers.

More significantly, volunteers with high NAI titers at baseline were better protected by the vaccine than those with high HAI titers: the disease was less severe, the duration of viral shedding and symptoms was shorter, and fewer and less severe symptoms were reported.

“This challenge study confirms the importance of NAI titer as a correlate and for the first time establishes that it can be an independent predictor of reduction of all aspects of influenza disease,” the researchers concluded. “This suggests that NAI titer may play a more significant role than previously thought and that neuraminidase immunity should be considered when studying susceptibility after vaccination and as a critical target in future influenza vaccine platforms.”

—Amanda Balbi

Reference:

Memoli MJ, Shaw PA, Han A, et al. Evaluation of antihemagglutinin and antineuraminidase antibodies as correlates of protection in an influenza A/H1N1 virus healthy human challenge model [published online April 19, 2016]. mBio. doi:10.1128/mBio.00417-16.