On April 25, 2009, the World Health Organization (WHO) warned of an outbreak in Mexico of what was then called swine flu and called for measures to prevent its international expansion.
What the health authorities did not know then is that the virus ( influenza A H1N1 ) had already reached Auckland, in New Zealand, on board a plane. Now, a study has modeled the risk that an infectious disease will spread during a flight. Although it is low, the probability of infection increases the closer to the first infected or if this is a member of the crew.
Hours before the WHO launched its alert on the new flu, a Boeing 747 from San Diego (USA) had landed at the Auckland airport. Among its nearly 400 passengers, a score of students who had been in northern Mexico returned. nine of them got on the plane and sick. 13 hours later, another five people, maybe eight, got sick from the plane.
In the following weeks, more than 1,000 people had to be hospitalised and during the entire pandemic, 49 New Zealanders died. By the end of 2009, 18% of the population of New Zealand had been exposed to the virus, that is, they carried antibodies against that strain of H1N1.
There is no way to know if, in those days, only those students brought the new flu to New Zealand, but “they were the first cases of pandemic flu known in New Zealand,” the epidemiologist from the University of Otago tells in an email ( New Zealand), Michael Baker. “They were detected on April 25, 2009, the same day that the WHO declared that the outbreak of the new A / H1N1 pandemic was a public health emergency of international importance,” he adds.
Baker was able to follow the boys and a hundred people who sat with them in the back of the plane. That monitoring allowed to verify that the passengers who became infected during the flight were no more than two rows away from any of the sick students, either forward, backward or lateral.
“The pandemic offered us a unique opportunity to investigate the risk of transmitting the flu during a flight, since it was a completely new virus in New Zealand, we knew that the only point it could come from was other passengers on that flight.” Then the New Zealand epidemiologist wrote. “It is reassuring to know that there were few infections and they only occurred among passengers who were close to the infected persons, suggesting that the transmission was caused more by droplets expelled when coughing or sneezing than by tiny aerosols dispersed through the air conditioning system. air-plane, “he adds.
“Respiratory diseases are often spread in populations through close contact,” recalls the professor in the nursing school at Emory University (USA) and the study’s lead author, Vicky Hertzberg.
“We wanted to determine the number and duration of social contacts between passengers and crew,” he adds.