The vaccine, invented in the 1930s, is highly effective — one dose normally provides lifetime protection. But it is not harmless. It cannot be given to newborns or anyone with a compromised immune system. It is given to people older than 60, pregnant women, or children younger than 8 months only when the risk of infection is high.
About one recipient in 100,00 suffers a dangerous reaction like jaundice, hepatitis or encephalitis, Dr. Marques said, and about one in a million dies. “If you vaccinate 30 million people, you’ll get about 30 deaths,” he said.
But if yellow fever infected 30 million people, two million could die.
So, with the disease moving rapidly forward, health authorities announced that they hoped to inoculate 95 percent of the population in 77 cities and towns in the virus’s path — a total of 23 million people, including 12 million in this city alone.
But “they didn’t have 12 million shots to give us,” said Dr. Wilson M. Pollara, São Paulo’s health secretary. “So we’re doing it in phases — two million at a time.”
The global vaccine stockpile, overseen by the World Health Organization, normally contains only six million doses, made by only four manufacturers, including the Cruz foundation.
But Brazil has scaled up its production to about 5 million doses per month and will soon be able to double that, said Dr. William Perea, the W.H.O.’s epidemic control coordinator.
That should easily cover Brazil’s needs for now, he said, so the global stockpile will not be drawn down. If necessary, it can be replenished; the four makers together can turn out 100 million doses a year in an emergency, he said.
Meanwhile, to stretch the vaccine it initially had on hand, Brazil gave out one-fifth doses. That provides protection for at least a year and can be used in emergencies, the W.H.O. says.