To date there have been 135 confirmed infections, 44 of which have been fatal. There have only been two cases over the summer, but experts worry the infections will pick up speed when temperatures start to drop in the fall.
When H7N9 cases proliferated at an alarming rate in early April, many flu experts worried whether a usable H7N9 vaccine could be made. The few previous studies of vaccines against flu strains carrying an H7 hemagglutinin — the protein on the virus's shell that gives it the H portion of its name — were dismal.
Even with massive doses — 12 times as much vaccine as used to protect against strains of seasonal flu — the vaccines didn't trigger much of an immune system response. Needing huge doses per person would severely limit the amount of vaccine available globally if a pandemic with H7N9 were to occur.
"This was always one of the real gaps we've had," Robinson says.
"We've been successful with (vaccines against) H9s, H5s, H1s, H2s, H3s and so forth. But H7s — we had tried before and we've just not had very good luck.''
But in the past few months there have been glimmers of hope. Animal studies have shown that when H7N9 vaccine is mixed with an adjuvant results were better. Just last week the Chinese flu vaccine maker Sinovac announced its trial H7N9 vaccine had been effective in animal studies and human testing would soon begin.
Robinson acknowledges he is more optimistic at this point that an H7N9 vaccine that has a practical dosing regimen could be made.
"If I had not seen some of those data, I would probably be as pessimistic as I would have been last year. But some of the animal data is promising and gives a little bit of hope there," he says.
Doses as small as 3.75 micrograms — one quarter of the dose used per strain in seasonal flu vaccine — and as large as 30 mcg will be tested, in a two-dose regimen. Because the virus is new to the human immune system, it is expected two doses will be needed.