Flu Scan for Apr 20, 2016

Influenza A, then B
;
Flu vaccine protection surprise
;
Global flu update

Study notes single-season influenza A infections followed by influenza B in kids

Austrian researchers who studied samples from 533 children with lab-confirmed flu during the 2014-15 season found that 13 of them (2.4%) were infected by influenza A, then subsequently infected with influenza B after they had recovered.

Writing yesterday in the Journal of Infectious Diseases, the investigators performed polymerase chain reaction (PCR) testing on 1,765 samples obtained from pediatricians and other primary care physicians. They confirmed flu virus in 647 samples, of which 533 were from children younger than 14 years.

Among this sampling was a subset of 33 pediatric patients who had previously been diagnosed as having influenza A but visited their pediatrician later with typical flu-like symptoms. Real-time PCR on samples from these children revealed that 13 of them had contracted influenza B.

The mean interval between the diagnosis of influenza A and B infection was 50 days (range, 24-70), and flu B infection in these children coincided with the peak prevalence of influenza B in the community.

The authors conclude, "It is striking that no observations similar to ours have been reported previously. One explanation can be that the 2014-2015 influenza season was quite unique as compared to previous seasons." They note that 2014-15 saw a high number of influenza B infections, and that the peaks of flu A and flu B were well separated.
Apr 19 J Infect Dis study

 

Study suggests assessing neuraminidase antibodies to predict flu vaccine performance

Raising questions about some of the conventional wisdom on flu vaccines, results from a small human-challenge trial suggest that measuring antibodies that target neuraminidase (NA) rather than those that target hemagglutinin (HA) might offer advantages) for predicting how well a vaccine might work.

A research team led by the National Institute of Allergy and Infectious Diseases (NIAID) published the findings yesterday in mBio. HA and NA are flu virus surface proteins.

Studies establishing hemagglutination inhibition (HAI) titers of greater than or equal to 1:40 as a correlate of protection were done in the late 1970s, but studies from recent flu seasons using the performance marker have suggested that vaccines are underperforming. Along with calls for better vaccines, experts have said more work is needed to understand correlates of protection.

To investigate the issue, scientists enrolled 65 healthy adult volunteers ages 18 to 50 years old, tested their blood to measure HA and NA antibodies, and grouped them by HA antibody level (25 in high and 40 in low). Each participant received a nasal inoculation of the 2009 H1N1 virus, and researchers then monitored their health and examined their blood samples in the Clinical Studies Unit at the National Institutes of Health Clinical Center in Bethesda, Md.

Not surprisingly, those with high levels of HA antibodies had significantly lower levels of mild-to-moderate flu with a somewhat shorter illness, compared with participants who had lower HA antibody levels. However, the two groups didn't differ much in terms of general flu symptoms.

The striking finding was that the baseline neuraminidase inhibition (NAI) titer correlated more significantly with all markers of disease severity and had a stronger independent effect on outcome, the authors said. Subjects who had high NA antibody levels had less severe disease and a shorter duration of viral shedding and symptoms.

The researchers concluded that HA and NA antibodies considered together might better predict mild-to-moderate disease or symptom severity than either measure alone, but NA antibody measures could be a stronger measure for gauging disease severity. They suggested that NA immunity should be considered when looking at flu susceptibility and that NA antigens should be considered in the development of new flu vaccine platforms.
Apr 19 mBio study
Apr 19 NIAID press release

 

Northern Hemisphere flu starting to taper, with spots of increased flu B

Flu activity in the Northern Hemisphere is sustained but continues to decrease, with several regions detecting increases in flu B, while areas of the Southern Hemisphere reported rising 2009 H1N1 and flu B detections, the World Health Organization (WHO) said in an Apr 18 update.

Sustained flu activity in North America is mostly attributable to circulating H1N1, though detections continue to decrease.

Flu levels in Europe are falling, with an ongoing shift toward detections of circulating flu B, especially in northern countries, the WHO said.

Activity remains elevated in northern temperate Asia, with increasing flu B detections, especially in Mongolia and South Korea. Flu levels remained low elsewhere in Asia, with the exception of elevated flu B in south China and Hong Kong.

Levels in the Southern Hemisphere remain low, with increasing H1N1 detections in tropical South America and elevated severe infections due to H1N1 in Central America and the Caribbean. Brazil reported higher-than-expected H1N1 activity, the WHO said. Increases in severe infections were detected in Argentina, Chile, and Paraguay. Colombia experienced high respiratory syncytial virus (RSV) detections.

In Africa, Tunisia reported elevated H1N1 activity, and Kenya saw rising flu B, the WHO said.

Globally, influenza A made up 54.5% of 23,402 flu detections in recent weeks, and of the 13,251 subtyped samples, 85.8% were the 2009 H1N1 virus, and 14.2% were H3N2. Of the 11,051 subtyped flu B samples, only 19.6% were from the Yamagata lineage, the B strain used in this season's trivalent Northern Hemisphere vaccines.
Apr 18 WHO update

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