Study findings showed that antibodies against the influenza surface protein neuraminidase are associated with a significantly shortened period of viral shedding in children and adults, and with shortened influenza symptom duration in adults, researchers reported in Clinical Infectious Diseases.
The researchers suggested that increasing anti-neuraminidase (anti-NA) immunity should be a priority for next-generation influenza vaccines.
“In our prior publication we looked at correlates of protection against infection and symptomatic infection with influenza in naturally exposed people. We found that while stalk and [hemagglutinin (HA)] head antibodies correlated with protection, NA antibodies did not. In this manuscript we examine the effect of various antibodies on illness and shedding duration,” Aubree Gordon, PhD, MPH, associate professor of epidemiology at University of Michigan’s School of Public Health, explained to Infectious Disease News.
“We found that NA antibodies were associated with shortened duration of both shedding and symptoms, meaning that, although in our study NA antibodies did not protect them from infection, people who were infected got less ill if they had higher levels of NA antibodies. In addition, given that they are sick for a shorter period and shed virus for a shorter period, it is likely higher levels of NA antibodies will impact influenza transmission.”
With an efficacy between 10% and 60%, the current seasonal influenza vaccine is “suboptimal” the researchers said. Unlike the HA head, which is currently targeted by influenza vaccines, NA evolves more slowly, which Gordon and colleagues suggested could “allow NA-based immunity to protect against otherwise drifted strains.”
In Managua, Nicaragua, the researchers conducted a case-ascertained community-based study of influenza virus transmission that included 170 cases of RT-PCR-confirmed influenza A(H1N1)pdm infection and 45 serologically confirmed infections among household members.
They found that pre-existing anti-NA antibody levels of 40 or more were associated with a shortened shedding duration of 69% (95% CI, 34%-85%) among adults with RT-PCR-confirmed infections. Additionally, an NA antibody level of 80 or more was associated with further shortened shedding and shortening of symptom duration by 82% for influenza-like illness (95% CI, 39%-95%).
When Gordon and colleagues assessed RT-PCR-confirmed infections in children, they found that hemagglutination inhibiting titers of 1:20 or more were associated with a 32% shortened shedding duration of (95% CI, 13%-47%).
From the results, the researchers suggested that anti-NA antibodies may play a large role in reducing the duration of influenza and may impact transmission. They noted that this effect appears “most clearly among adults.”
“We hope that the addition of [NA] to the influenza vaccine would improve effectiveness and would be especially important in years when the virus-vaccine ‘match’ is not good,” Gordon said. “That is when the HA included in the vaccine does not match the main HAs that are circulating. Our results support that addition of NA to the vaccine would lessen symptoms in individuals and might also lower transmission.” – by Marley Ghizzone
Disclosures: Gordon reports receiving consultancy fees from the CDC, outside the submitted work. Please see the study for all other authors’ relevant financial disclosures.