Flu vaccine: How it finds its way into the needle

Stephanie Chester, M.S.

While the annual flu vaccine saves thousands of lives every year, most people don’t give much thought to the work that takes place behind the scenes to determine what’s in that injection. The US has a system for national influenza surveillance which collects data from across the US to identify which influenza viruses are circulating, if the current season’s vaccine is a good match, and which viruses should be included in the next year’s vaccine. 

Preparations for next season’s flu vaccine start at the beginning of each flu season. In fact, it is the specimens collected at the beginning of each new flu season that help inform vaccine virus selection for the next year. Public health laboratories play a critical role in this process.

When a patient goes into the doctor with a fever, cough, sore throat and other flu symptoms, the doctor will likely test them for influenza. Some doctors act as sentinel providers, which means they regularly submit specimens collected from patients with flu-like symptoms to public health laboratories for influenza surveillance. Public health labs can also receive specimens from a variety of other submitters including hospital/clinical laboratories, university student health centers, long-term care facilities, commercial laboratories and many more.

State or local public health labs then test the submitted specimens for influenza.  They characterize the influenza virus down to the specific flu subtype using a real-time reverse transcriptase PCR (RT-PCR). These test results are reported to CDC and help inform what specific types and subtypes of influenza are currently circulating in the country and locally. This helps CDC and state/local public health officials determine if this year’s vaccine is effective at protecting us from what is actually circulating.

The public health lab then selects a subset of specimens to submit for national surveillance.  This subset is grown up in virus culture and further characterized to determine exactly which influenza viruses are predominant and thus should be included in next season’s vaccine. Each February, CDC, in collaboration with the World Health Organization and other countries, uses real-time RT-PCR data, sequencing analysis and viral isolate characterization results to determine which viruses to include in the Northern Hemisphere’s vaccine for the next season.

As you can see, a lot of effort goes into national influenza surveillance and vaccine virus selection, and public health labs are integral in this process. Even with this season being so mild and slow to start, the diligent work of public health labs and their health departments ensured that specimens arrived at CDC consistently and on time to help inform vaccine virus selection.

We, at the Association for Public Health Laboratories, are grateful for the hard work and dedication of all the public health lab personnel and public health officials who consistently perform exemplary work to support our national influenza surveillance system. Their work on influenza alone impacts all our lives, from informing our communities and physicians about circulating flu viruses to helping to determine what goes into that annual prick in our arm. They deserve to be celebrated!

Stephanie Chester, M.S., is the manager of influenza programs at the Association of Public Health Laboratories (APHL).

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