Health care workers should be first in line when vaccines against the swine flu virus are ready and approved, an expert panel at the World Health Organization concluded in a meeting last week. The Strategic Advisory Group of Experts on immunization (SAGE) also said countries should consider vaccinating various other groups—such as those most at risk of death and disease—but said each country should map out its own strategy, depending on what it hopes to achieve and how much vaccine it has available.
SAGE held a special meeting on 7 July to discuss the evolving pandemic and vaccine development. A summary of its recommendations, endorsed by WHO Director-General Margaret Chan on 11 July, was released in a statement today and discussed during a press briefing (audio file) by Marie-Paule Kieny, head of WHO's Initiative for Vaccine Research.
Protecting doctors, nurses, and other medical staff is the key to keep healthcare systems running, SAGE concluded. If countries have enough vaccine, they can reduce disease and death by vaccinating groups at higher risk, such as pregnant women, those with chronic health conditions, or even all healthy young adults between 15 and 49 years old, the age group that appears most vulnerable. They can also choose to try to slow the transmission of the virus, in which case vaccinating healthy children is an option, Kieny says, because they are an "amplifier of transmission."
Meanwhile, the amount of vaccine available globally could be much lower than hoped due to a problem in the production process. Kieny said that for reasons that aren't fully understood, vaccine companies that use eggs to grow vaccine viruses get yields of only 25% to 50% of those obtained during the production of seasonal vaccine. WHO's network of influenza labs is currently producing a new set of seed viruses that Kieny hopes will result in higher yields. If they succeed, delivery of the vaccine need not be delayed, Kieny said, because regulatory agencies are likely to accept the clinical trials expected to being soon* with the low-yield strains, even if high-yield strains are used to produce vaccine. But if yields remain low, it would take many more months to produce the billions of vaccine doses WHO is hoping for, according to Kieny's presentation at the SAGE meeting.
Total vaccine supply will depend on several other unknowns, including whether 15 micrograms of antigen is enough—as is the case with seasonal vaccine—and whether one or two shots are needed. A key factor is how many companies will use so-called adjuvants, which boost the immune response and thus lower the amount of antigen needed per shot. A recent survey among 36 vaccine producers, also presented by Kieny, showed that only 12 of the 33 proposed vaccine formulations will contain an adjuvant. Many companies have never used adjuvants and adding them now would raise additional safety issues, Kieny said. "It's very difficult to mix antigen from one company with adjuvant from another company when they have never been tested together."
*The trials are not currently under way as previously reported.