Twice a year, the World Health Organization convenes an expert panel to decide what should go into vaccines for the coming flu season in each hemisphere, based on the highest-circulating strains. It takes six months to decide which strains to include, purify the seed ingredients, mass produce the shots in eggs and get them into vials to go into arms.

The steps add up to a sluggish ability of vaccine makers to adapt to the fast-evolving virus, meaning last year’s vaccine may not protect against this year’s strain. And the respiratory disease is highly contagious, in most cases causing fever, coughing and body aches, but potentially leading to severe complications like pneumonia.

Another part of the problem is that many flu viruses originated in birds, virologists say.

“You’re growing it in embryonated chicken eggs,” said Dr. Lynora Saxinger, an infectious diseases specialist at the University of Alberta in Edmonton. “And so that’s avian cells that are growing the virus for you and the virus actually adapts to grow better in the avian cells.”

That can sometimes result in viruses that look less like what’s causing infections in humans, which can further decrease the effectiveness of influenza vaccines, said Matthew Miller, director of the Degroote Institute for Infectious Disease Research at McMaster University in Hamilton, Ont.

The article then discusses a few other technologies that are in the works, and their respective pros/cons