One of the NEJM studies also showed that many older Americans as well as recipients of the 1976 swine flu vaccine may already be protected against the new virus. In that study, researchers from the U.S. Centers for Disease Control and Prevention (CDC) report that tests of serum taken from 1976 swine flu vaccine recipients showed a strong protective immune response against today's pandemic virus. The findings may help to explain why the virus sickens children and young adults more than older people, the authors wrote. The preexisting immunity may also prime 1976 vaccinees to respond vigorously to the new pandemic vaccine.I got my shot in 1976, as did someone I know, so we won't be getting it again...freeing up at least two doses for some kids with asthma or those with weakened immune systems.
"It would certainly be something very interesting to look at," says Jackie Katz, senior author of the study. "That's why we did these studies originally, to help inform the public health response."
Adults appear protected
Since the new H1N1 virus emerged earlier this year, health officials have noted how it has disproportionately struck children and young adults and conspicuously spared older people worldwide. The disparity is most dramatic in the U.S.: 79 percent of laboratory-confirmed cases have been in people under 30 years old, whereas only two percent of cases have been in adults over 60. The U.S. median age of pandemic infections so far is 12, but somewhat higher in other countries. The median age of confirmed cases in Australia is 21, for example.
Since May, Katz, who is chief of the CDC National Influenza Division's Immunology and Pathogenesis Branch, has been testing stored serum samples to look for existing immunity to the new virus in the U.S. population. Her group's latest report shows that serum from adults born before 1930, including survivors of the 1918 pandemic, possesses antibodies that recognize and respond powerfully to the novel H1N1 virus.
With an antibody concentration of 40 or more considered protective (immunologists describe antibody responses in terms of serum dilution ratios, such as 1:40), the tests showed that 100 percent of subjects born between 1910 and 1929 mounted antibody levels of 80 or more. Only 34 percent of subjects born before 1950 mounted comparable levels, suggesting that exposure to the 1918 pandemic virus or its immediate descendents in the 1920s and 1930s conferred the strongest protection against the new flu.
The original swine flu
The CDC group also started over the summer to test 83 samples of serum drawn in 1976 from adults who received a single dose of the swine flu vaccine as well as a handful of samples from children who got the 1976 vaccine. The study found that the serum from 52 (63 percent) of the adult subjects produced antibody levels of 160 or more when exposed to the novel H1N1 virus. That number was nearly as many (59) of those whose serum demonstrated a strong response when exposed to the 1976 swine flu itself.
The NEJM report notes that a Japanese study recently reported finding protective antibody responses against the novel H1N1 virus in Japanese adults exposed to the 1918 pandemic virus, but not in subjects born after 1920. Serum from older Europeans tested by the CDC also showed lower response levels than the U.S. samples, possibly indicating a greater level of protection among Americans from the 1976 vaccine, which was given only in the U.S.
Given the current shortages of vaccine, I hope the Centers for Disease Control would try to spread the word about health benefits of the 1976 shot more vigorously.