The question of vaccination for Influenza (H1N1) in pregnancy is frequently asked. A small study published by NIH does provide some answers around this.
Why all the concern about pregnancy?
To date there have been 100 pregnant women hospitalized with H1N1 in the US this season. 28 deaths have occurred in this group. This is an alarmingly high proportion for this healthy group (28% of admissions!). Though the total numbers seem very small it is the proportion of deaths in this important group that is high. Why is this group more important than other? To say the obvious; too many other lives depend on these women. A pregnant women is likely to have other children at home, those children are not only at risk for illness from mother but if mother is incapacitated or worse dies can changes the social structure of the home and future lives of her young children. Loss of life in other groups of people as traumatic as it may be does not carry as great a social burden as losses in this group can. This group is therefore at highest priority to be vaccinated.
Do pregnant women have adequate response to vaccination?
The study does show that pregnant women do mount an adequate response to a single dose of inactivated injectable vaccine and it is well tolerated. The 15mcgm dose appears to provide adequate response in 92% of recipients and 30mcgm in 96% of recipients. the pool sizes were very small at 25 women in each group.
The H1N1 2009 vaccine is made in an identical process to the existing seasonal influenza vaccine. It is a killed vaccine, therefore cannot cause H1N1. It is also thiomersal free.
In this day of rising health care costs it is reasonable to ask the question if mass immunization costs are worth it? It may be worth it if it only decreases the number of deaths and hospitalizations from influenza related illnesses. Some benefit appears to be from vaccinating on a community level to create herd immunity.
So what is herd immunity? Think of a group of persons in a large room. If a virus is introduced into the room it can infect the first person, multiply, infect say 3 more, multiply these 3 will infect 9 more, and so on. However if some of the persons in the room are immune to the virus then it cannot multiply in that immune individual. If more and more persons are immune in that room then it becomes very difficult for viruses to spread as it runs out of susceptible persons. If enough persons in a group are immune then the few persons with less immunity like the elderly really start to benefit from the immunity of the herd.
An estimate of this was made by Weycker et al they estimated that a 20% vaccination rate among children would decrease the number of influenza cases by 46% and an 80% coverage would be needed to decrease the disease by 91%. This is a significant finding. This can be done, as has been proven in the case of small pox where high levels of vaccination literally cornered the virus until it had no one to infect. As of december 1979 there are no human cases of small pox.
In Ontario Canada Jeffery Kwong et al did show improvement in hospitalization, emergency room visits for pneumonia and influenza like illnesses. This study was undertaken after Ontario decided to provide free influenza vaccination to all of its citizens in 2000. The study was conducted on data collected from all hospitalizations and ER visit for pneumonia and influenza like illnesses between the years 1997 and 2004. Vaccination rates increased to 38% of population from the pre 2000 rates of about 18% coverage. The data was compared to other Canadian provinces with similar population sized in the same year which had 24% vaccination coverage rates. During this time hospitalizations and deaths from influenza related illnesses decreased throughout Canada but the decrease was more pronounced in Ontario. Ontario saw 74% reduction in influenza related deaths compared with a 57% reduction in other provinces. In this study the rate of hospitalizations and ER visits was 40% less in Ontario than in other provinces. The group that saw the greatest benefit from vaccination with reference to ER visits, hospitalization and physician ER visits were the 50-64 yr age group they saw up to 80% less healthcare visits. The difference becomes much less obvious as we look at older groups that probably have other medical problems and respond less favorably to vaccination. Notably no significant increase in side effects or Guillian barre were seen in Ontario.
The societal cost savings can also be measured in terms of days lost at work, child care etc. This was shown in a study done by Bridges et al. That showed that even in years where there is a poor match between circulating virus and vaccine a net societal cost of $65.59 per person was seen in terms of lost wages compared with no vaccination. Whereas in years that a close match is seen a net societal cost of $11.17 per person is seen. These are very small prices to pay for improvement in healthcare cost.
In conclusion, there are reductions in healthcare costs with adequate vaccination though this is not seen at the individual level especially when community vaccination rates are low.
Both vaccines are effective. They are manufactured with similar ingredients and both have chicken eggs in them.
Live intranasal vaccine
1. At least in children appears to provide 30-50% greater immune response.
2. Easy to administer- no needles
3. No evidence that transmission of live virus to contacts occurs. Still would recommend precautions if taking care of patient with recent bone marrow transplant.
4. Not approved for 49 years or pregnancy
5. Should be avoided if taking other live vaccines such as MMR, shingles vaccine at the same time
6. Inactivated vaccines can be given with it, such as seasonal influenza
7. Should avoid Tamiflu for 48 hours before and 2 weeks after vaccine
Inactivated injectable vaccine
1. Lower response rate
2. Needs injections
3. Better safety data in the over 49yrs and in pregnancy
4. Can be given ages 6 months and up
5. Can be given with other vaccines
6. Can be given to very immunocompromised patients
7. Tamiflu does not interfere with it
The basic make up of the H1N1 vaccine is no different from the influenza vaccine we receive every year. Same parts, same process, same packaging and the same delivery.
What is different is that combination of antigens that are present in H1N1 are novel, new and unique.
H1N1 appeared on the scene too late after the seasonal influenza constituents were agreed upon in this years vaccine. Plus it was too late to include it in the seasonal vaccine process, therefore a separate vaccine was added.
What makes the vaccine different is its antigenic structure. An analogy for this may be to think of the virus as having a lock on it. The vaccine gives us the right key to unlock the virus and hence kill it. H1N1 was sneaky this time around and changed to tumblers (the antigens) in the lock to something we never had to encounter before. Same virus with same basic biological structure, same inner workings, infecting the same cells, multiplying in the same way and killing in the same way, just using a different code. So rather than use one of the known “keys” we already have on our keychain that worked for the influenza “lock” in the past, we had to come up with a new key (vaccine antigens) to work with the H1N1 lock combination. Remember same kind of lock (virus target), same material for the key (vaccine), same keyhole (targets of the vaccine), just different key pins (the antigens).
Therefore the side effect profile, route of administration, efficacy and safety should be about the same as traditional influenza vaccination.
Shame on you H1N1 for trying to pull a fast one on us this time. Fool me once (in 1918) shame on you, fool me twice shame on me.
For more information on the new H1N1 vaccine see the CDC website.
There are two basic kinds of viruses, those that are made of DNA, the stuff we are made of and RNA viruses. These are viruses that contain a more primitive form of genes.
DNA tends to more stable and reliable from generation to generation. Hepatitis B and Small Pox are examples of DNA viruses.
Influenza on the other hand is an RNA virus and a very unstable RNA virus when compared to other RNA viruses. When it invades a host cell it creates million of copies of itself. In the process it kills the host cell. But because RNA virus have poor error checking due to the lack of a proofreading enzyme called DNA polymerase the copies of itself are very sloppy. Over 80% of these copies are unusable and are not infectious. The remaining ones are infectious to other cells but are still not exact copies of the mother virus. They are therefore “quasi-species” that is; they are very similar but not exact. Over time the virus gradually changes in its genetic makeup.
Our immune system recognizes an invader as alien by its genetics. The specific site on the virus that our antibodies recognize is called the “epitope”. If the genetics of the virus change too much i.e. change the epitope then our immune system takes longer to get into action, sometimes too late. If our immune system has been primed to recognize the viruses epitope from recent experience like a vaccination which is exposing that epitope to our antibody factory. This is akin to getting the floor plans. Then our immune system will shift into high gear much quicker because of the headstart. Hence the need for revaccination every year with a virus that is as close to the current strain as possible.
Plus the antibodies that we do make do not stay around in ample supply forever. In the case on Influenza the antibodies last about 4-5 months. This is also why the sickest people should not get vaccinated too soon before the season. After october 1st is generally a good time to get vaccinated that way we can face the influenza season with the optimal quality and quantity of antibodies.