“What happened is, in the development of the vaccine, as we grow it in eggs, the virus itself mutated a bit, so that there was almost an accidental mismatch purely on the basis of the virus trying to adapt itself to growing in eggs,” Dr. Anthony Fauci told WTOP. “That’s what happened in Australia and it is likely that that’s what we’re going to see here.”

The doctors added that the ineffective shots had the lowest rate of success in preventing influenza A. The flu strain – also known as H3N2 – “historically is always the worse influenza,” according to Dr. Fauci and can result in severe illness and possibly death in at-risk patients. Among the most at risk for complications from the flu include seniors over 65 years old, children under age five, and pregnant women.