Flu Vaccine With Four Inactivate Strains More Effective Than Similar One With Less

New research published in the journal Vaccine shows that a flu vaccine that includes four strains of inactivated influenza could be more protective than a similar one containing only three.

Researchers at Saint Louis University found that adding a strain of influenza B helped to improve the effectiveness of a flu vaccine nasal spray and a traditional intramuscular vaccine that's injected as a shot in the arm muscle.

Furthermore, the studies showed, via the addition of the B strain, that it helped improve the antibody response to the strain and didn't weaken the body's immune response to other flue strains in the vaccine.

Some flu vaccines can be trivalent, meaning they contain two strains of influenza A and one of influenza B-or quadrivalent-including two strains of A and two of B. Both of which are available to fight influenza.

Each year alone, scientists create a flu vaccine based on the strains of influenza that they predict will circulate the next season. Unfortunately, the virus that's in the vaccine doesn't always match the circulating strain of influenza.

As it stands, there are two lineages of B flu strains, and about 50 percent of those in the past decade, the trivalent vaccine B strain did not match the circulating B one, with the quadrivalent vaccine in both B strains in it.

"We found adding a fourth strain to the vaccine increases the chance the vaccine will match the circulating flu B strains," Gorse said. "At the same time, the addition didn't compromise the vaccine's ability to protect against the other three strains and was just as safe. Over time, the four-strain vaccine may be an important strategy to provide improved protection against influenza."

During the study, 3,355 volunteers who were between 18 and 64 years of age were vaccinated at 38 sites in the United States. They were randomized to receive one of three vaccines: the quadrivalent flu vaccine that contained two A flu strains and both lineages of the B strains; the licensed trivalent intradermal vaccine for the 2012-2013 flu season; or an alternate trivalent intradermal vaccine that contained two A strains and the B strain that was not in the licensed seasonal flu vaccine.

Those who received the quadrivalent vaccine had superior antibody responses to the B strains and equally robust responses to A strains when compared to those who received the trivalent vaccines that did not contain the corresponding B ones. 

Furhermore, researchers found that adding another B strain didn't compromise the vaccine's ability to cause the body to mount an immune response to the other flu strains. The responses were given the quadrivalent vaccine via the same as those of volunteers who received it with two strains of A and the strain of B that was matched to the B strain in 2012-2013 seasonal flu trivalent vaccine.