WHO: Many nations report brisk flu activity, with influenza B rising

Most countries with flu seasons under way are reporting moderate levels compared with past seasons, with some reporting hospitalization and intensive care unit admission levels at or above earlier seasons, the World Health Organization (WHO) said yesterday in its latest global flu update.

And while H3N2 is still the predominant strain, the proportion of influenza B is gaining, a pattern seen in the latter part of flu seasons, though several Northern Hemisphere countries have reported early, brisk influenza B activity.

Nations urged to strengthen flu steps

The WHO urged countries reporting flu cases or entering their flu seasons to take steps to shore up case management, compliance with infection control measures, and vaccination of high-risk groups against the disease. The agency also posted an updated fact sheet on seasonal flu, which covers vaccination and the use of antivirals to prevent or treat the disease.

In its activity update, the WHO said though flu vaccines might not provide full protection, "they remain the best line of prevention and should be offered as long as influenza is circulating." It added that the agency expects currently circulating seasonal flu strains to be susceptible to oseltamivir and zanamivir, two neuraminidase inhibitors that are the gold standard for treating flu.

Mixed picture of predominant strains

In North America, Canada and the United States are reporting that seniors account for most cases and hospitalizations. In Canada, the proportion of influenza B detections are on the rise, and in the United States and Mexico, H3N2 is predominant.

In Europe, flu levels are well above baselines in most regions, except for eastern Europe. Influenza B is the most common strain, though some countries and surveillance systems are reporting different influenza A patterns. For flu hospitalizations, UK indicators are at high levels, mostly from H3N2 and influenza B Yamagata lineage, and France is reporting its highest level over the past five seasons, mostly from 2009 H1N1 and influenza B.

Some parts of the world are reporting notable increases in 2009 H1N1 activity or a mix of that strain and influenza B, including Algeria, Tunisia, Egypt, Iraq, and Israel. In Iran, flu levels are rising, with all subtypes detected.

In eastern Asia, China is reporting high levels of flu activity—outstripping the past three seasons—in both the northern and southern parts of the country. Illnesses have mostly been caused by influenza B, followed by H3N2, according to the WHO. Hong Kong's percentage of respiratory specimens testing positive for flu has passed its threshold, with influenza B most common. Meanwhile, Southeast Asia continued to report low flu activity.

In tropical locations of the Americas, flu levels mostly remained low except in Ecuador, which reported a recent rise in 2009 H1N1 activity.

Southern Hemisphere temperate-zone countries continued to report flu at interseasonal levels.

At the global level through the first week of January, influenza A was detected in 62.3% of flu-positive samples, and, of subtyped strains, 58.9% were H3N2 and 41.1% were 2009 H1N1.

Of the characterized influenza B viruses, 89.2% belonged to the Yamagata lineage, which isn't included in trivalent versions of the Northern Hemisphere's seasonal flu vaccine.

See also:

Jan 22 WHO global flu update

WHO flu fact sheet

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