Researchers found that individuals who reported receiving the 1976 vaccine mounted an enhanced immune response against both the 2009 pandemic H1N1 virus and a different H1N1 flu strain that circulated during the 2008-09 flu season.
It is unclear if the response was enough to protect against the 2009 H1N1 virus, but the study points to a lingering benefit. The findings also raise hope that those vaccinated against the 2009 H1N1 pandemic strain might also enjoy a similar long-term advantage.
"Our research shows that while immunity among those vaccinated in 1976 has waned somewhat, they mounted a much stronger immune response against the current pandemic H1N1 strain than others who did not receive the 1976 vaccine," said Jonathan A. McCullers, M.D., an associate member of the St. Jude Infectious Diseases Department and the study's lead author.
The study was conducted in August 2009 before a vaccine was available against the pandemic H1N1 flu strain and before the virus was circulating widely in the Memphis, Tenn., metropolitan area, where study volunteers lived.
116 St. Jude Hospital employees and spouses age 55 and older participated in the study. The group included 46 vaccinated in 1976 against the H1N1 flu virus, known as A/New Jersey/76, which sickened more than 200 military recruits in New Jersey. That outbreak triggered fears of a flu pandemic and led to a massive government effort to quickly produce and distribute a vaccine.
Researchers reported that nearly 90 percent of volunteers made antibodies able to recognize a key protein on the surface of both the 2009 pandemic and the 2008-09 H1N1 flu strains. Those antibodies were present in numbers large enough to meet one federal gauge of vaccine effectiveness.
Nineteen percent of volunteers also produced antibodies that neutralized the 2009 pandemic strain and blocked it from infecting cells. In comparison, more than 67 percent of volunteers had antibodies that neutralized the 2008-09 seasonal H1N1 strain.
Those vaccinated in 1976 were more likely to make neutralizing antibodies against the new pandemic strain. More than 17 percent of the 1976-vaccine group made such antibodies in large quantities. Only about 4 percent of those who had not received the 1976 shot had comparable levels of antibody production. The difference between the two groups was statistically significant, meaning it was unlikely chance alone explained the result.
The unexpectedly robust immune response mounted by all the participants suggests that routine vaccination against seasonal flu might confer a broader-than- realized protection, McCullers said. The St. Jude volunteers included many health care workers who are vaccinated annually against flu.
Citation: McCullers et al., 'Recipients of Vaccine against the 1976 “Swine Flu” Have Enhanced Neutralization Responses to the 2009 Novel H1N1 Influenza Virus', Clinical Infectious Disease, April 2010; doi:10.1086/652441