1. This year's flu vaccine is the same as last year's vaccine. If you are healthy and got the vaccine last year, you probably still have antibodies against all 3 strains.
2. The antigen used for the 2009 Swine Flu vaccine was an H1N1 hemagglutinin. It was used as a single antigen vaccine in 2009, but was included as one of the three hemagglutinin antigens in 2010 and 2011. In 2009, in some countries, a novel adjuvant was added to the antigen (either MF59 [Novartis] or ASO3 [Glaxo]) to increase the immune response.
In the US, for example, which used no adjuvant, the 2010 and 2011 flu vaccines contain the 2009 swine flu vaccine, plus two more antigens. Therefore, claims that this year the vaccine is entirely different are misleading.
In countries like Ireland and England, which used the ASO3 adjuvant in 2009, the current flu vaccine differs from 2009 because it has no ASO3. But it does have the same hemagglutinin antigen. [I mistakenly wrote adjuvant instead of antigen earlier.]
Narcolepsy cases have occurred after both adjuvanted and unadjuvanted swine flu vaccines were given.
3. How effective is the vaccine? Although 70-90% of recipients develop antibodies, the amount of flu that is prevented is questionable. Remember that studies from Hong Kong and Canada found that if you got flu vaccine in 2008, you were about twice as likely to become ill with a swine flu infection the next year? So the 2008 vaccine had negative efficacy for the 2009 influenza. (Being vaccinated in 2008 made it more likely that recipients would get sick from flu the next year. This is not strange, as some vaccines, in the past, have been found to enhance infection. )
UPDATE: Here is a new article, just published, which supports a causal relationship between getting the 2008 flu vaccine and actually getting sick from swine flu the following flu season.
The effectiveness of the flu vaccine varies from year to year, but it is not very high, and never over 70% for the young and healthy. It is hard to show any efficacy in the aged.
4. The reason narcolepsy was discovered to be a side effect of swine flu vaccine in Finland was because there were 13 times as many cases appearing as usual. That is 1300% more cases than expected, of a very serious condition that can have lethal consequences.
5. Was narcolepsy the only serious adverse reaction to swine flu vaccine? It's unlikely. There is no data on other side effects, except for Guillain Barre Syndrome (GBS). Because GBS was caused by the 1976 swine flu vaccine (see prior posts on this from 2009), CDC and FDA promised to look closely for cases when the 2009 swine flu vaccine program was launched. The same level of scrutiny was not paid to other potential side effects.
You may have seen headlines that swine flu vaccine does not cause Guillain Barre Syndrome; I did, on the same day a report was issued about narcolepsy and the vaccine. However, It seems swine flu vaccine DID cause Guillain Barre Syndrome after all. The full text is here, or you can read the abstract below. CDC calculated it caused 1.77 times as many cases of GBS as expected, or 177%.
MMWR Morb Mortal Wkly Rep. 2010 Jun 4;59(21):657-61.
Centers for Disease Control and Prevention (CDC).
Guillain-Barré syndrome (GBS) is an uncommon peripheral neuropathy causing paralysis and in severe cases respiratory failure and death. GBS often follows an antecedent gastrointestinal or upper respiratory illness but, in rare cases, can follow vaccination. In 1976, vaccination against a novel swine-origin influenza A (H1N1) virus was associated with a statistically significant increased risk for GBS in the 42 days after vaccination (approximately 10 excess cases per 1 million vaccinations), a consideration in halting the vaccination program in the context of limited influenza virus transmission. To monitor influenza A (H1N1) 2009 monovalent vaccine safety, several federal surveillance systems, including CDC's Emerging Infections Program (EIP), are being used. In October 2009, EIP began active surveillance to assess the risk for GBS after 2009 H1N1 vaccination. Preliminary results from an analysis in EIP comparing GBS patients hospitalized through March 31, 2010, who did and did not receive 2009 H1N1 vaccination showed an estimated age-adjusted rate ratio of 1.77 (GBS incidence of 1.92 per 100,000 person-years among vaccinated persons and 1.21 per 100,000 person-years among unvaccinated persons). If end-of-surveillance analysis confirms this finding, this would correspond to 0.8 excess cases of GBS per 1 million vaccinations, similar to that found in seasonal influenza vaccines. No other federal system to date has detected a statistically significant association between GBS and 2009 H1N1 vaccination. Surveillance and further analyses are ongoing. The 2009 H1N1 vaccine safety profile is similar to that for seasonal influenza vaccines, which have an excellent safety record. Vaccination remains the most effective method to prevent serious illness and death from 2009 H1N1 influenza infection; illness from the 2009 H1N1 influenza virus has been associated with a hospitalization rate of 222 per 1 million and a death rate of 9.7 per 1 million population. [This suggests 3,000 people in the US died from swine flu -- a far cry from the 24,000-45,000 said to die each year from influenza.--Nass]