Monday, November 8, 2010

Vaccinating Kids Against the Flu Helps Others - More Evidence

2010-2011 and The Elderly
History says 2010-2011 influenza should just be 2009 H1N1. That's not happening. The mix of infecting strains that are 2009 H1N1 (great antigenic matches to vaccine), a new H3N2 type (great match) and influenza B (very good match) isn't clear. The better the match, the more likely the vaccine will work.  That's good for those under 65, bad for those older.
The MMWR study also found that during seasons when influenza A (H3N2) viruses were prominent death rates were more than double what they were during seasons when influenza A (H1N1) or influenza B viruses predominated. In addition, the study confirmed previous findings that about 90% of influenza associated deaths occur among adults 65 years and older.
Typing of strains in the US from the start in October (week 40 to week 43) (information will change week by week) has 83 H3, 30 2009 H1N1 and 90 influenza B.  CDC International Surveillance update as of November 4, 2010 (link is to current information which will change) has Canada reporting predominantly H3N2 strains.  China is also predominantly reporting H3N2 strains.

The elderly were protected last year because they had either vaccine or natural infection protection against 2009 H1N1. They don't have protection against H3N2 that's new this year. So much more so than last year, they need to be vaccinated. In the US, consider Fluzone HD.

Source drying and Herd Immunity
Elsewhere I've plugged a great article from the World Health Organization that explains many of the concepts relevant to vaccines and vaccination.   In particular, the related concepts of source drying and herd immunity  called in the WHO article herd protection. Herd immunity/protection requires vaccinating (getting the vaccine) a high enough percentage so that the percentage actually immunized (prevented from becoming infected) stops the disease from spreading amongst those who are still susceptible.  When there is herd immunity, an outbreak will not occur.
The explanation of source drying from the WHO article is worth quoting in full:

Source drying is a related concept to herd protection. If a particular subgroup is identified as the reservoir of infection, targeted vaccination will decrease disease in the whole population.
In North Queensland, Australia, there was a high incidence of hepatitis A in the indigenous population. Vaccination of indigenous toddlers, with catch-up up to the sixth birthday, had a rapid and dramatic impact in eliminating the disease in the indigenous population and in the much larger non-indigenous population (who were not vaccinated) across the whole of Queensland.35 Similar approaches have been very successfully applied in several other larger settings, including Israel and the USA.36The success of source drying justifies vaccination of special occupational groups, such as food handlers, to control typhoid and hepatitis A.37
Pertussis vaccine boosters for close contacts (such as parents, grandparents, nannies, siblings and baby unit nurses), who are the most common sources of transmission to infants, protect those too young to be given primary vaccination with a surrounding “pertussis-free cocoon”.38
For a vaccine to be effective, it needs a strong response from the immune system.  That's a major problem with protecting the elderly against influenza because they have weaker immune systems that don't respond as well to vaccination.  One answer, being tried in the EU (FluId/Intanza 15mcg) and the United States (Fluzone HD) for the 2010-2011 influenza season is vaccines with higher amounts of virus stuff.  Fluzone HD has 60mcg of each of the 3 strains in the trivalent vaccine as compared to the normal 15 mcg.  FluId/Intanza uses a teeny tiny needle that goes into the skin only.  Regular FluID/Intanza has 9 mcg per strain while the vaccine for the elderly has 15mcg per strain.

What else can be done?  Vaccinate infants and children against influenza not only to protect themselves but  also to protect others.   There is the Japanese experience of mandatory vaccination of school children. It resulted in many fewer deaths from influenza in the elderly.

In 2010, there was the study in JAMA Effect of Influenza Vaccination of Children on Infection Rates in Hutterite Communities  The full article is free.
Immunization of children and adolescents aged 3 to 15 years with the trivalent influenza vaccine formulated for the 2008-2009 influenza season conferred 61% indirect protection against influenza among persons who did not receive the study vaccine. The protection conferred to all study participants was similar. Our data suggest that a significant herd immunity effect can be achieved when the uptake of vaccine is approximately 80% in clusters in which children and adolescents aged 3 to 15 years are immunized...
Conclusion: Immunizing children and adolescents with inactivated influenza vaccine significantly protected unimmunized residents of rural communities against influenza.
Now there's a new study in the Journal of Infectious Diseases that shows vaccinating 50% of school children makes a big difference to others. The editorial comment   A Paradigm for the Control of Influenza and the major article  Direct and Indirect Effectiveness of Influenza Vaccination Delivered to Children at School Preceding an Epidemic Caused by 3 New Influenza Virus Variants are free.
From the editorial comment:
The study by Glezen and colleagues investigates the effectiveness of immunizing 47.5% of elementary‐school children 5–11 years old in 25 public schools and 3 parochial schools in which 1 dose of live attenuated influenza vaccine (LAIV) was administered (intervention group), relative to a comparable community in which vaccine (LAIV or trivalent inactivated vaccine [TIV]) was administered in an off‐protocol manner. A significant degree of herd protection (reduction in the number of medically attended acute respiratory illness [MAARI]) was seen in all age groups except 12–17‐year‐olds, with risk ratios for all age groups >18 years old being lower even than that for the target group of 5–11‐year‐olds. This occurred despite there being an excess of persons >75 years old in the intervention community. Furthermore, LAIV was 1.7 times more effective in the prevention of proven influenza virus infection in the target group than among those who received TIV and was 6 times more effective than among those who did not receive vaccine.
The editorial is worth reading in full.

Cross-protection in the face of new influenza variants
The influenza season studied was 2007-2008 and the infecting viruses found in the study region in Texas were not antigenically similar to those in the vaccine.  So it isn't surprising that the injected inactivated influenza vaccine wasn't very effective.  However, Flumist, the Live attenuated influenza vaccine (LAIV) was effective in protecting both the school children and others in the community. LAIV, as expected, provides much better cross-protection in the face of new influenza variant.

2010-2011
What about this flu season? As usual, there are three strains in the 2010-2011 seasonal flu vaccine.  There's the same vaccine strain used last year for 2009H1N1. There's a new strain of H3N2 for infecting strains of H3N2 that are new this year.  And there's the same influenza B strain as last year.   Since, as expected, there hasn't been much change antigenically in 2009 H1N1 it will be a great match.  Because it is a new type of H3N2, the strains haven't  had time to mutate and will also be a great match to the vaccine.  There is only influenza B vaccine strain and two families of influenza B strains.  So far it looks like most strains of influenza B that are infecting are from the vaccine virus family --- so it is a very good match.

Protecting Others
The Flu Vaccine is very, very safe.  Those concerned with thimerosal (although they shouldn't be) can vaccinated with thimerosal free vaccine.  Flumist, the LAIV vaccine doesn't contain thimerosal.  This is the first year that Flumist has been licensed in Canada.  Because there is an antigenic match between the infecting strains and the vaccine strains, the choice between LAIV and the injected TIV is less important.  But in any case, get vaccinated.  Not just for yourself, but to protect those who aren't protected well by influenza vaccine.

2 comments:

  1. Nice summary of newer evidence. Thanks.

    Some antivax people quote the Cochrane collaboration review studies on flu vaccine as a way of trying to diminish the role of vaccines. Yet in the last few years there have been a number of newer studies showing flu vaccination does help reduce flu infection and mortality.
    In a few more years, there would likely be a change in outcome would the cochrane reviews be repeated.

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  2. Oh' that's great! I agree that "Vaccinating Kids Against the Flu Helps Others " using that idea helps to avoid spreading of flu from other people. Thanks for sharing this post. I learned a lot.

    -mel-

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