The ineffectiveness of this year’s current flu vaccine was evident when Australia, whose flu season runs from May through October, resulted in more than two-and-a-half times the number of laboratory confirmed notifications of influenza reported to the National Notifiable Diseases Surveillance System (NNDSS) this year when compared with the same period last year.
In the Northern Hemisphere, flu season typically begins in October and runs through April and sometimes, even May. Peak months for the flu in the U.S. occur between December and March, according to the Centers for Disease Control and Prevention (CDC).
Why the flu vaccine may not be as effective as we believe
Of course, we know that flu viruses mutate, and we have seen examples of this happening, especially in bird flu viruses. And that is the nature of the beasts.
However, government health officials have been concerned with the degree of the ineffectiveness of flu vaccines manufactured every year for the following year’s flu season. The 2016-2017 vaccine was only 43 percent effective against the predominant influenza A H3N2 strain, and protection has been almost as low in other years.
One difference stood out – Ineffectiveness was not seen in flu vaccines manufactured without the use of chicken eggs in the process. It was suggested that the A H3N2 virus possessed an adaptive mutation that affected egg-grown vaccines. And the adaptive mechanism was found by scientists based at the University of Pennsylvania School of Medicine. It affects a hemagglutinin (HA) protein that occurs in H3N2 viruses.
The research was published in the Proceedings of the National Academy of Sciences on November 6, 2017, and highlighted the challenges associated with producing influenza vaccine antigens in eggs, while offering a possible explanation for why there was such a low degree of effectiveness in last year’s flu vaccine.
“The 2017 vaccine that people are getting now has the same H3N2 strain as the 2016 vaccine,” noted Scott Hensley, Ph.D., an associate professor of microbiology at the Perelman School of Medicine at the University of Pennsylvania. “So, this could be another difficult year if this season is dominated by H3N2 viruses again.”
How are flu vaccines made?
For over 70 years, the flu vaccine has been made by injecting strains of the flu virus into chicken eggs. The eggs are then allowed to incubate, and in turn, this allows the virus to replicate. The fluid in the eggs is then removed and purified to get enough of the virus strain to make the vaccine.
But scientists also have known that when viruses are grown in chicken eggs, they also evolve in these egg hosts. They adopt genetic changes that help them grow in the egg environment. And this is apparently causing problems with the end product.
“During the 2014–2015 influenza season, clade 3C.2a H3N2 viruses possessing a new predicted glycosylation site in antigenic site B of HA emerged, and these viruses remain prevalent today,” wrote the article’s authors.
The 2016-2017 vaccine included a clade 3C.2a H3N2 strain, but the egg-adapted version of the viral strain lacked the new site. “Here, we biochemically demonstrate that the HA antigenic site B of circulating clade 3C.2a viruses is glycosylated,” say the authors.
Scientific American explains all the medical details very simply – In 2014, the H3N2 virus began wearing a new molecule on one of its surface proteins. The molecule is a type of sugar, hence the reason it’s being called a glycosylation site. The fact that the sugar molecule is chemically glued to a site on the virus’s surface close to where human antibodies, our immune system watchdogs attach is important.
That sugar makes its hard for our antibodies to attach to the virus and kill it, and protect the virus from destruction. Interestingly, the sugar-adorned viruses are not found in vaccines made using other methods. There are currently two non-chicken egg flu vaccines made in the U.S. One is FLUCELVAX, and is grown in canine kidney cells, and the second, Flublok, is grown in insect cells.
“Current H3N2 viruses do not grow well in chicken eggs, and it is impossible to grow these viruses in eggs without adaptive mutations,” Dr. Hensley explained. “Our data suggest that we should invest in new technologies that allow us to ramp up production of influenza vaccines that are not reliant on eggs.”
The research paper cited in this story is titled: Contemporary H3N2 influenza viruses have a glycosylation site that alters binding of antibodies elicited by egg-adapted vaccine strains, and was published in the Proceedings of the National Academy of Sciences.
