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Flu Vaccine Benefits Go Beyond Effectiveness of One Strain

December 11, 2017 2 comments
LJ TanGuest post by Litjen (LJ) Tan, MS, PhD; co-chair and co-founder of the National Adult and Influenza Immunization Summit.

 

There seems to be a lot of speculation recently about how effective the influenza (flu) vaccine will be at preventing cases of influenza this season.

We have heard suggestions that the vaccine may only be 10% effective against flu this year, that there may be mismatches in the vaccine compared to the influenza strains that are circulating, and thus, that the vaccine is not worth getting.

To address these concerns I will start with a basic explanation of flu and flu vaccines, and then discuss the factors that play into vaccine effectiveness.

First, let me say that influenza is a serious respiratory infection that is responsible for about 30% of all the respiratory infections during the winter season. When I say serious, I mean that flu can keep you down for a week or more, and you will feel completely miserable. Additionally, each year thousands of people of all ages die from flu in the U.S.; it can be very dangerous. So, that office colleague who said that he was out with the flu yesterday very likely did not have influenza. Not fully understanding the dangers of flu is why some people fail to see the value of flu prevention.  

Flu is caused by multiple strains of influenza viruses that circulate during the winter season; specifically, we have influenza type A (with the H3N2 and H1N1 strains) and influenza type B (there are two type B strains that can circulate and currently 90% appear to be the Yamagata lineage, but since it is still so early in the season and sample sizes are small, this data point may not be statistically significant). Because these strains of flu viruses can switch every season in terms of dominance, and can also mutate, manufacturers need to develop a new influenza vaccine every year and people need to be re-vaccinated each year.

To be clear, the vaccine development process is the same every year, it is just that the starting, or “seed”, vaccine virus that we immunize against has to be identified before it can be used to develop our country’s annual vaccines.

When that seed virus is identified, it is then amplified (or passaged) to develop more seed virus. Then that seed virus is further amplified to create the large quantities of vaccine virus that we ultimately need to prepare an adequate supply of vaccines to protect our population. That amplification of the seed virus, and the making of large amounts of vaccine virus, can occur in eggs, which is the more traditional way, or it can also occur in cell cultures. So there needs to be four seed viruses developed and amplified to create influenza vaccines – an H3N2 seed, an H1N1 seed, and the two B seed viruses.

So why do we keep hearing people say that this year’s flu vaccine may only be 10% effective? Where did that suggestion come from?

When we say that a flu vaccine is 10% effective, what we usually mean is that it was effective in preventing 10% of cases of influenza in those who were vaccinated. This 10% number that you may have heard is actually a data point from Australia, and it’s not against all strains of flu, but specifically against the H3N2 strain that dominated the southern hemisphere this past flu season. If you look at the Australian data for all influenza, the vaccine effectiveness goes up to 33%. Agreed, that’s not great for Australians (although, it’s still better than no protection), but is looking at the Australian data truly reflective of what might happen in the US?

It’s unlikely, and here’s why. Read more…