The CDC has found that about 8% of the Type B influenza viruses that have been collected and characterized in the United States this year are from the Yamagata lineage. Protection against this strain of influenza is not included in the seasonal vaccine. As a result, even those who have been given the influenza vaccine may contract this Type B strain. Luckily, Type B influenza makes up only about a third of the influenza viruses collected so a very small percentage of the flu viruses in the population will not be covered by the vaccine. A few cases slipping through the cracks is normal because the vaccine only protects against three strains of the flu each year as recommended by the WHO. My personal takeaway is that it is still important to wash you hands whether you get the flu vaccine or not.