Do Quadrivalent Flu Vaccines Really Work?

Despite their remarkable effectiveness, influenza vaccines have faced their share of challenges over the years.

Predicting which influenza strains will predominate next year is based on a scientific yet fallible process. When a vaccine contains few or none of the circulating viruses, its efficacy is low.

Influenza B vaccine strains did not match circulating strains in 6 flu seasons between 2000 and 2011.

Since 2012, quadrivalent influenza vaccines (QIV) containing both circulating B lineages of influenza have been available. To determine the impact of QIV use, a multinational team of flu experts developed a model simulating the multiyear influenza dynamics for 2000-2013.

One strength of this model is that it considered inflenza’s transmissible nature and multiyear immunity acquired by infection and interaction between B lineages due to natural or vaccine-induced cross-protection.

The bottom line was that QIV worked well. In fact, if QIV had not been available, Americans would have contracted 16% more B lineage cases of flu, the researchers concluded.

The model further found that QIV prevents an average of 172 cases annually per 100,000 Americans, which translates to 482,000 fewer flu cases per year. Elderly patients 65 years or older and young seniors aged 50 to 64 years benefit most from QIV, with 21% and 18% reductions in B lineage cases, respectively.

The researchers were quick to point out that influenza vaccination coverage is greater in those aged 50 years or older, which may account for this finding. Regardless, higher coverage should allow QIV to prevent even more flu cases than trivalent influenza vaccines (TIV).

Using relatively conservative estimates of TIV-induced cross-protection, the researchers’ model still showed a very significant reduction in B influenza cases.

Influenza vaccine coverage has improved in recent years, and if this trend continues, then the researchers believe it will improve the QIV vaccine’s impact.

Their study was published in the August 2015 issue of Influenza and Other Respiratory Viruses.