The flu vaccine is effective

According to a recent article in Eurosurveillance, this season’s influenza vaccine is only 10% effective. News of this potentially life-threatening vaccine failure predictably went viral, undoubtedly discouraging many from getting the vaccine at all. The problem is that this type of vaccine-based fear-mongering is both dangerous and misrepresents the science. It’s dangerous because influenza remains one of the leading causes of morbidity and mortality each year, and misrepresentative because there are multiple influenza vaccines on the market, all of which are designed to protect against multiple strains of flu.

Vaccination is enduringly the best way to protect yourself, your family, and society from influenza. Full stop.

So where did these vaccine effectiveness estimates that I’m calling inaccurate and dangerous come from? While the influenza season in the US is just starting to come on strong, the flu season is nearly over in Australia — where influenza outbreaks occur during our summer. And in Australia, the most commonly used vaccine — the same one primarily being used in the US now — did not work well against a specific genetic lineage of H3N2 influenza. (For a primer on influenza subtypes, see this excellent NPR article, and for information on the genetic lineages of influenza, see

The phylogenetic — or evolutionary — relationship between H3N2 viruses. The colors represent different antigenic types, i.e. they might respond differently to vaccination. This image was taken from The author of this essay had no part in the generation, analysis, nor visualization of these data. See Neher & Bedford 2015 for details.

However, the influenza vaccine in question is designed to protect against four different flavors of influenza, and the research that is cited for demonstrating 10% effectiveness against specific forms of H3N2 also shows that the vaccine was 50% effective at preventing infection by H1N1 and almost 60% effective against two subtypes of influenza B. These estimated levels of protection are comparable to seasons where the vaccine was deemed highly effective by the CDC and the World Health Organization.

Unfortunately, so far this year, the most prevalent strain of influenza currently spreading in the US is the H3N2 virus, the same genetic linneage that caused problems in Australia. There, the vaccine was somewhere between 0 and 40% effective against this virus (the average was 10%, as reported in Eurosurveillance).

But here’s where things get interesting: it turns out that a newly licensed vaccine, Flucelvax, which is now available in the US but wasn’t available during the flu season in Australia, appears to be highly effective against the currently circulating H3N2.

Both the CDC and the Eurosurveillance paper report that the Flucelvax vaccine should protect against infection from H3N2, including the genetic lineages 3C.2, 3C.2a, and 3C.3. The difference lies in how each vaccine is manufactured. The vaccines used in Australia (the same vaccines used in the US except for Flucelvax) are developed by growing the virus in eggs. As a result of this process, the vaccine strain accumulates genetic mutations, which renders it less effective. The Flucelvax vaccine, on the other hand, is manufactured using cell culture, which is how most of our other viral vaccines are made. In this process, the virus doesn’t pick up as many mutations, and the mutations it does accumulate are less likely to affect vaccine efficacy.

Each week during the influenza season, the CDC releases a detailed surveillance report on the current state of the outbreak. This report includes laboratory-based estimates of whether the influenza vaccine is protecting against currently circulating strains. According to this week’s report, “A (H3N2): Phylogenetic analysis of the HA [hemagglutinin] genes from 256 A(H3N2) viruses revealed extensive genetic diversity with multiple clades/subclades co-circulating. The HA genes of circulating viruses belonged to clade 3C.2a (n=198), subclade 3C.2a1 (n=56) or clade 3C.3a (n=2). 68 influenza A(H3N2) viruses were antigenically characterized, and 67 (98.5%) A(H3N2) viruses tested were well-inhibited (reacting at titers that were within fourfold of the homologous virus titer) by ferret antisera raised against A/Michigan/15/2014 (3C.2a), a cell propagated A/Hong Kong/4801/2014-like reference virus representing the A(H3N2) component of 2017–18 Northern Hemisphere influenza vaccines.”

In plainer speak, the CDC results suggest that the cell-based influenza vaccine Flucelvax should be highly effective against H3N2 viruses. The Eurosurveillance paper found similarly high effectiveness for the cell-based Flucelvax (in addition to the infamously low predicted effectiveness for the egg-based vaccine). The agreement between the Eurosurveillance results and the CDC surveillance report strengthens the evidence that Flucelvax could protect against the circulating H3N2 viruses.

It is true that the vast majority of individuals in the US will be vaccinated with the older, egg-based vaccine this season, and thus won’t be highly protected against the currently circulating H3N2 viruses. But it is not true that this means the influenza vaccine this year is ineffective — even the egg-based versions. Those who receive the vaccine will be highly protected against H1N1 and influenza B, other common strains appearing in the US this season. These vaccinated individuals will also contribute to herd-immunity and can protect those most likely to have severe complications from influenza infection. A vaccine with less-than-perfect effectiveness still protects its recipients and their social contacts.

So in light of this more complete understanding about the effectiveness of influenza vaccination, what should you do? First, get vaccinated (and if you have the option, ask for the Flucelvax vaccine). Second, take someone with you to get vaccinated because they’re more likely to spread infection than you are. Finally, stop the vaccine fear-mongering. When we spread rumors based on partial truths, we discourage individuals from taking responsible, proactive health measures. Like all currently licensed vaccines, the influenza vaccine, in all its forms, is effective. Vaccines have saved millions of lives and improved the quality of life for billions. They are our most effective measure against infectious diseases and one of the marvels of humanity.


Feld, Scott L. “Why your friends have more friends than you do.” American Journal of Sociology 96.6 (1991): 1464–1477.

Neher RA, Bedford T. 2015. nextflu: real-time tracking of seasonal influenza virus evolution in humans. Bioinformatics 10.1093/bioinformatics/btv381.

Paules, Catharine I., et al. “Chasing Seasonal Influenza — The Need for a Universal Influenza Vaccine.” New England Journal of Medicine(2017).

Sullivan, Sheena G., et al. “Low interim influenza vaccine effectiveness, Australia, 1 May to 24 September 2017.” Eurosurveillance 22.43 (2017): 17–00707.

Acknowledgments, Caveats, and Miscellany

I received invaluable editorial advice from Laura Beerits.

The reality of influenza vaccination is far more complicated than I had time to discuss and I am also not a medical doctor.

Lastly, and despite what you may be thinking, I am not on the board of Flucelvax nor do I have any financial or intellectual conflicts of interest related to influenza vaccines.