But matching strains in the vaccine with those circulating among humans during a flu season is a notoriously unpredictable exercise.

What made it troubling, Dr. Aylward said, was that his family had lived for several years in an illegal encampment on the outskirts of Mecca, so he must have caught a strain circulating in Saudi Arabia.

The strains circulating in Latvia appear to have originated from both Russia and Western Europe while those in Estonia appear to have originated in Russia.

In contrast to strains circulating in Southeast Asia, EMA viruses are derived from a progenitor that has the PB2 627K mutation.

Bacterial strains circulating in hospitalized populations may be genetically distinct from those circulating in the general human population [13,17,49].

Health authorities are using a new monovalent oral vaccine that needs fewer doses to create immunity to type 1 polio, the strain circulating in Yemen.

The researchers say that all current strains circulating in the world are directly related to the medieval bacterium.

Avian flu (H5N1) strains in China and southeast Asia are now resistant to amantadine, although strains circulating elsewhere still seem to be sensitive.

Dr. Castro cited two recent outbreaks of such tuberculosis in high schools in Georgia and California, each from strains circulating abroad.

It is different from strains circulating among poultry in Southeast Asia and Indonesia.