WASHINGTON – A substantial portion of elderly Americans may have some immunity to the swine-origin H1N1 influenza virus, a finding that may prove useful when and if a vaccine to the new flu strain becomes available.
The questions of whom to target with a swine flu vaccine, and how to stretch the supply if it is limited, are among the most important issues facing public health officials over the next four months.
Scientists at the Centers for Disease Control and Prevention announced Thursday that a study using stored blood samples found that one-third of people over 60 have antibodies that might protect them from infection with the new virus. If further research is able to better define who has partial immunity, those people might need only one dose of vaccine, not two.
“Our working hypothesis is that everyone who gets this vaccine is likely to need two doses,” Anne Schuchat, CDC’s deputy director, said Thursday. She added, however, that the new study suggests “perhaps there will be some people where pre-existing immunity will be there and one dose would lead to a ‘primed’ response. That is definitely … something we’re interested in.”
If a swine flu vaccine is produced, only about 2 billion doses would be ready by next fall, the World Health Organization estimates. Public health authorities presumably would recommend it be given to people at greatest risk for severe illness and death.
As of Thursday, the United States had 5,764 confirmed cases and 9 deaths, in 48 states. Epidemiologists believe, however, that more than 100,000 people have been infected since the new virus came to public attention a month ago.
Worldwide, 41 countries have reported 11,034 cases and 85 deaths – numbers that are almost certainly also an undercount.
The blood study, published Thursday in CDC’s Morbidity and Mortality Weekly Report, gives an immunological explanation for a surprising observation in the swine flu outbreak: very few old people are getting sick.