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Computer Prediction: Only Vaccine Can Stop Flu Pandemic -- but Strategies May Buy Time


Pandemic Flu Vaccine: Best Hope Not Yet Here

"A vaccine certainly could blunt the impact so that less than 50% of the population gets infected if a substantial proportion is immunized," Burke says.

There's only one problem here: such a vaccine doesn't yet exist. It may be years away. But so may the next flu pandemic. Even if the H5N1 bird flu -- now quickly spreading in Asian, Middle Eastern, and European birds -- learns to spread among humans, there's no way of knowing when it will happen or how bad it really will be.

When there's a vaccine against a pandemic form of flu, it won't have to be perfectly effective to save millions of lives. But it will have to work quickly. The vaccine currently being tested takes two immunizations several weeks apart. That won't be fast enough to stop a flu pandemic, the computer model predicts.

That's also the prediction of biostatistician Hulin Wu, PhD, chief of the division of biomedical modeling and informatics and director of the center for biodefense immune modeling at the University of Rochester in New York.

"Once you discover this kind of new strain of virus, it is already too late to develop a new vaccine," Wu tells WebMD. "People have to manufacture the vaccine the year before for it to be effective. And then you have to vaccinate people."

Flu Drugs Not Likely to Stop Pandemic

Antiviral drugs get a lot of press -- and many people have stockpiled their own personal stash of Tamiflu. But the computer model shows that there aren't enough antiviral drugs in the world to stop a flu pandemic.

"Antivirals require a huge amount for prevention," Burke says. "They certainly can work, but they are only useful for the 10 days you are using them to prevent infection. The total amount needed to impact the epidemic would be a huge amount, well beyond what is available."

Fortunately, there is a third strategy. Scientists call it "social distancing." Social-distancing techniques include quarantine of ill people and their families, closing schools and workplaces, and restricting travel.

Time-Honored Methods Buy Time

"Social distancing strategies can slow the epidemic to give us time for vaccinations and such, but are unlikely to completely shut off the transmission," Burke says. "After vaccination, the second most effective scenario is to target interventions to lessen person-to-person contact, whether this means isolation to homes or closing schools and workplaces. This can lower the peak number of people infected, but it doesn't mean fewer infections -- it just spreads them out a little more over time."

Even so, that would be an important thing to do. Slowing how quickly the infection spreads over time would reduce the peak surge in people desperately needing health care. It might just keep public health efforts from being overwhelmed. And it might buy precious time.

"If we are lucky, we may be able to take advantage of flu's seasonality," Burke says. "Flu is a seasonal disease. It occurs in winter everywhere. If there are some weather and climate factors that influence transmission, even if you did nothing and summer came along, the epidemic might go away for awhile. So if can we can string the epidemic along so not everyone is infected in that first winter, then summer starts to work to your advantage and you get another four to six months to get people vaccinated."

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