It is expected that providers and practices that have signed up to become distributors for Novel H1N1 Vaccine will start getting vaccine soon. It is the hope that vaccination is widespread and can be given to all people who desire it. However, there may be shortage of vaccine in the early weeks, requiring triage of who is most in need of vaccination. As of right now, the CDC recommends that the following people have priority for vaccination:
- Pregnant women because they are at higher risk of complications and can potentially provide protection to infants who cannot be vaccinated;
- Household contacts and caregivers for children younger than 6 months of age because younger infants are at higher risk of influenza-related complications and cannot be vaccinated. Vaccination of those in close contact with infants younger than 6 months old might help protect infants by “cocooning” them from the virus;
- Healthcare and emergency medical services personnel because infections among healthcare workers have been reported and this can be a potential source of infection for vulnerable patients. Also, increased absenteeism in this population could reduce healthcare system capacity;
- All people from 6 months through 24 years of age
- Children from 6 months through 18 years of age because cases of 2009 H1N1 influenza have been seen in children who are in close contact with each other in school and day care settings, which increases the likelihood of disease spread, and
- Young adults 19 through 24 years of age because many cases of 2009 H1N1 influenza have been seen in these healthy young adults and they often live, work, and study in close proximity, and they are a frequently mobile population; and,
- Persons aged 25 through 64 years who have health conditions associated with higher risk of medical complications from influenza.
If initial supplies are inadequate to immunize all the patients in the above group, the following groups should have first access to vaccine:
- pregnant women,
- people who live with or care for children younger than 6 months of age,
- health care and emergency medical services personnel with direct patient contact,
- children 6 months through 4 years of age, and
- children 5 through 18 years of age who have chronic medical conditions.
Once the highest risk people are immunized, recommendations will likely grow to include all people 25 to 64, and finally to people 65+. Unlike seasonal flu, Novel H1N1 (pandemic flu / swine flu) is actually less likely to strike older patients due to their likelihood to having been exposed earlier in their life (last outbreak of a related strain was 1974!)
It should also be noted that while many strains of seasonal flu are resistant to oseltamavir (Tamiflu), Novel H1N1 (Swine Flu) is typically oseltamavir sensitive. Patients or providers exposed to H1N1 patients may benefit from post exposure prophylaxis with Tamiflu. Articles are being published weekly on new resistance in both Novel H1N1 and Seasonal Influenza A H1N1 and H3N2. Check the CDC website for the most up to date information!
New data is being published in the upcoming issue of the New England Journal of Medicine on the immune response associated with the new Novel H1N1 Flu Vaccine, and in the interest of public health it has already been distributed on the web.
Three articles will be published, two on the ability of various dosages of the vaccine to create an immune response, and a third on the presence of immune antibodies in people exposed to previous seasonal flu vaccines, and to past outbreaks of natural H1N1 “swine” flu.
The bottom line:
1) A single 15 microgram dose of the novel H1N1 vaccine creates an adequate immune response in near 100% of people within 14 days of administration. There will be no need to have a second shot. CDC guidelines will likely be changed to reflect this.
2) People who were immunized to the seasonal flu last year in the Northern Hemisphere have no or low chance of having immunity to Novel H1N1 (swine) flu. People who were immunized with the southern hemisphere vaccine last year have some chance of immunity, but still should get the new vaccine this year.
3) People who were exposed to previous pandemic flu strains often have resistance to this pandemic flu. Today’s novel H1N1 pandemic flu strain is likely related to the flu strains that caused outbreaks in 1918 and 1976. Older patients are more likely to have been exposed to one of these outbreaks and be immune today. Still, there are enough people in that age group that are not immune (higher than 50% in many cases) that all people should be immunized if possible.
Response after One Dose of a Monovalent Influenza A (H1N1) 2009 Vaccine — Preliminary Report. Greenberg ME, Lai MH, Hartel GF, Wichems CH, Gittleson C, Bennet J, Dawson G, Hu W, Leggio C, Washington D, Basser RL.N Engl J Med. 2009 Sep 10.
Cross-Reactive Antibody Responses to the 2009 Pandemic H1N1 Influenza Virus. Hancock K, Veguilla V, Lu X, Zhong W, Butler EN, Sun H, Liu F, Dong L, Devos JR, Gargiullo PM, Brammer TL, Cox NJ, Tumpey TM, Katz JM. N Engl J Med. 2009 Sep 10.