Seasonal Influenza Vaccines: maybe a reason not to get one
I’ve been pretty vocal recently about the need for vaccination; it is without doubt one of the single greatest advances in medicine, and has saved millions of lives due to prevention of infectious disease. A news report in Science Daily summarizes a research paper from the Journal of Virology, and suggests that some influenza exposure is beneficial in the long run.
As we found earlier in this forum, seasonal influenza vaccines are necessary due to the rapid change that we observe with wild populations of the virus. Immunity to influenza does not give complete protection to the next year’s influenza, and it is therefore critical that we protect the most susceptible of our population (mainly the elderly, and otherwise immunocompromised) from catching the flu in the first place. Now as we found out in the epidemiology story from a few weeks ago, the dynamics of the virus in human populations is complex, and is influenced by other similar viruses that can trigger cross-reactive antibodies that can quickly eliminate one virus from the population. This would suggest that bona fide exposure to influenza by catching the disease can offer some advantages in the long run that someone who has only been exposed via vaccination doesn’t have.
This report examines a population of vaccinated versus non-vaccinated Dutch children. When the researchers compared these two groups, they found that the number of T-cytotoxic cells reactive with influenza antigens rose with age in the non-vaccinated children, and these cells did not in the vaccinated group. The lack of increase in the vaccinated group is not surprising, because the antigens given in the vaccine typically trigger a significant antibody response (B cells and T-helper cells) and not a T-cytotoxic response that requires viral infection to initiate. The antibody response is of course protective; antibodies against the virus prevent viral attachment and infection in the first place. The antibody response is specific to those antigens, and do not offer significant protection for the subsequent year’s influenza virus.
What the researchers found though was that the T-cytotoxic cells in the non-vaccinated group recognized a number of cross-reactive antigens, and did offer some protection against other influenza subtypes. This offers the intriguing possibility that exposure in young children to these antigens by infection with seasonal influenza might be important in long term survival to pandemic influenza. Rogier Bodewes, the corresponding author of the stud,y does not propose that it would be useful to reduce the level of seasonal influenza vaccination, but instead suggests that it would be more useful to develop a “universal” influenza vaccine that might offer more a more useful level of cross-reaction against influenza subtypes.
This is a very interesting study, carried out using properly controlled patient populations, and it has suggested a significant difference in an immunologic marker that might offer protection in the long term. However, the patients would have to be followed for many generations to see if their cellular-mediated immunity offers any real protection to influenza subtypes. It’s important to remember that the people born between 1880 and 1910 had plenty of exposure to seasonal influenza subtypes, and presumably developed a good robust cell-mediated response to a variety of influenza antigens, in the absence of any vaccination. However, that response was pretty ineffective at preventing them from dying in the great Influenza pandemic of 1918.