Flu Vaccines Are Less Effective

The effectiveness of flu vaccines has long been questioned, but a recent study suggested their drop in success is because they’re made inside chicken eggs.

According to the study, vaccine strains grown in eggs typically have mutations that increase the virus’s attachment to chicken cells.

Flu Vaccines Are Less Effective Because They’re Grown Inside Eggs, Study Says

By Ada Carr weather.com

The effectiveness of flu vaccines has long been questioned, but a recent study suggested their drop in success is because they’re made inside chicken eggs.

According to the study, vaccine strains grown in eggs typically have mutations that increase the virus’s attachment to chicken cells.

“How you prepare the vaccine can have profound effects on how humans respond to it,” study leader and University of Pennsylvania scientist Scott Hensley told NBC News.

Hemagglutinin is one of the reasons the flu itself is so effective, as it is what helps the virus bind to cells and infect them.

Most vaccines target this substance, but an oddly mutated virus seen by the researchers when creating vaccines inside of eggs caused the flu to develop a large sugar compound on top of the hemagglutinin, according to the study. This stops the body from responding to the vaccine.

“This is a mutation that has never been seen before,” Hensley told NBC News.

For years, medical professionals have been aware that the way vaccines are made is slow and error-prone. Additionally, it can be difficult to keep up with the virus, as they mutate every year.

“Any influenza viruses produced in eggs have to adapt to growing in that environment and, hence, generate mutations to grow better,” Scripps Research Institute scientist Ian Wilson told NBC News.

According to Hensley, the viruses won’t grow at all until they have mutated.

“This has been a big problem for a while, but it becomes a particular problem over the past few years,” he said. “H3N2 grows very poorly in eggs.”

Researchers have been developing flu vaccines inside eggs for over 70 years, according to the Centers for Disease Control and Prevention (CDC). In this process, a virus strain is injected into fertilized eggs, which are then incubated for several days while the virus grows. Then, they purify the virus to either weaken or kill it to create the vaccine.

According to the researchers, several mutations take place when flu viruses are grown in eggs, and these contribute to poor performances from the vaccine.

“We propose that differences in glycosylation between H3N2 egg-adapted vaccines and circulating strains likely contributed to reduced vaccine effectiveness during the 2016–2017 influenza season,” wrote the scientists. “Furthermore, our data suggest that influenza virus antigens prepared via systems not reliant on egg adaptations are more likely to elicit protective antibody responses that are not affected by glycosylation of antigenic site B of H3N2 HA.”

“We examined antibodies in humans that received the egg-adapted vaccines, and compared them to people who got vaccines made using insect cells,” said Hensley. “Sure enough, we found the vaccine prepared in insect cells produced better immune responses.”

Fauci told NBC News that the best methods of producing vaccines wouldn’t rely on growing a virus at all. Instead, they would involve using a piece of genetic material – a process that would also be much quicker.

New pandemic strains of the flu have emerged every couple of decades, according to the CDC. When a newer strain comes out, few immune systems can defend against it. This affects more people and can cause even more serious diseases. The last such virus was the H1N1 swine flu that broke out in 2009.

“Every time there’s a pandemic, we always find we are behind the 8-ball in terms of never getting the vaccine ready before it peaks,” said Fauci.

Medical experts are hoping for a vaccine that would protect humans against all flu strains, even as they mutate, and that might not need to be administered every year, according to NBC News.