1976 'swine flu' vaccine may offer pandemic H1N1 protection

Apr 26, 2010 (CIDRAP News) – The long-derided "swine flu" vaccination campaign of 1976, infamous for its association with cases of paralyzing Guillain-Barre syndrome, may have had a benefit that went undetected for more than 30 years. According to work published Apr 23, it may have protected recipients against the 2009 pandemic strain of flu.

Scientists from St Jude Children's Research Hospital in Memphis reported in the online edition of Clinical Infectious Diseases that people who received the 1976 vaccine produced a much more robust immune response against the novel 2009 strain than people of the same age who were not vaccinated back then. They also produced a stronger immune response against the seasonal H1N1 strain that circulated in 2008-09, which was replaced by the 2009 pandemic strain.

Taken together, the authors say, those results suggest that vaccination with a closely related strain of flu may confer some protection when vaccines against a circulating strain do not exist—such as in the early months after a pandemic strain first emerges, before the vaccine-manufacturing system can respond.

The study results arrive against a backdrop of observations and some laboratory reports from last winter that all describe older adults as less likely to have become infected with the novel 2009 flu.

In the study, 116 Memphis residents aged 55 to 73—110 members of the St Jude staff and 6 spouses—donated blood samples to check whether they possessed antibodies that would cross-react with flu strains from the past 2 years. Forty-six of the 116 had been vaccinated in 1976 against the novel swine H1N1 that surfaced that spring at Fort Dix in New Jersey, sickening 200 military recruits and killing 1 of them.

The vaccination campaign that was launched as a result of those cases inoculated 45 million Americans against the perceived threat of a new flu pandemic. The feared pandemic never arrived—the flu did not spread beyond Fort Dix—but more than 500 people, about 1 in 100,000 of those vaccinated, developed Guillain-Barre.

In the current research, the volunteers' blood was collected before the 2009 pandemic reached Tennessee, meaning that they were not likely to have been exposed to the new flu and developed an immune response to it. Under normal circumstances, according to the Centers for Disease Control and Prevention (CDC), about 1 person per 1 million who receives flu vaccine is at higher risk for the temporary but potentially fatal paralyzing syndrome.

When the volunteers' blood was analyzed using two tests, hemagglutination-inhibition assay (HAI) and microneutralization titer (MN), they were found to possess robust immunity against the 2008-09 seasonal strain. Those antibodies, however, were cross-reactive but non-neutralizing—not protective—against the 2009 pandemic strain.

However, those who had taken the 1976 vaccine were different. They also mounted significant neutralizing antibody responses against the 2009 pandemic strain, with some of them demonstrating MN titers of more than 160, four times the number that is the agreed-upon correlate of immunity. But it is not clear, the authors say, whether that antibody response would actually have protected the volunteers against 2009 infection.

The authors are careful to say that the reaction shown by the study subjects is probably not the explanation for the low rates of illness seen during the 2009 pandemic among elderly adults. Not enough vaccine was distributed in 1976 to exert that effect, they said, and the low 2009 infection rate has also been observed in countries that never used the 1976 vaccine. In addition, they caution that, as healthcare workers, the volunteers come from a group that receives frequent flu shots and is probably not representative of the general population.

But because the 1976 strain was only related to, and not identical to, the novel 2009 virus, the results may lend support to a hypothesis that has been periodically advanced during pandemic-preparedness planning: the idea that in time of scarcity, even a related vaccine from a past season may be of some help until a perfectly matched vaccine arrives.

McCullers JA, Van De Velde LA, Allison KJ, et al. Recipients of vaccine against the 1976 "swine flu" have enhanced neutralization responses to the 2009 novel H1N1 influenza virus. Clin Infect Dis 2010 (published online Apr 23) [Abstract]

See also:

CDC, "General questions and answers on Guillain-Barre syndrome (GBS)"

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