- For Immediate Release:
This statement was corrected on Feb. 16 to remove a reference to CDC data in the sixth paragraph.
Seasonal flu has been widespread this year, impacting millions of people across the country. It has been an especially challenging season, with high rates of hospitalization for both influenza and its complications, which include pneumonia and the exacerbation of chronic conditions such as asthma and congestive heart failure. Many schools have closed in an attempt to control the spread of the illness and doctors’ offices are packed with patients seeking diagnosis and antiviral treatment.
This year much of the illness has been caused by one strain of influenza A called H3N2, with another strain of influenza A called H1N1 and strains of influenza B contributing to lesser extents. The flu is a respiratory illness caused by several types and strains of influenza virus that infect the respiratory tract in humans, which includes the nose, throat and lungs.
Vaccination is one of the best ways known to protect against the flu. However, because of the severity of this season, there have been questions raised about how well this year’s flu vaccine worked. Although the initial report of 36 percent overall efficacy for this year’s vaccine in the United States that has been reported by our colleagues at the U.S. Centers for Disease Control and Prevention (CDC) is better than some might have predicted, there is still clearly significant room for improvement. The FDA is committed to working together with the scientific and medical communities to better protect the public against the flu and apply lessons learned to next season’s flu vaccines.
Because influenza viruses can change their genetic make-up rapidly during the course of a single year, seasonal influenza vaccines are unlike most other preventative vaccines, in that the strains contained in the vaccine constantly need to be adjusted based on the viruses that are expected to be in circulation. Public health experts do their best each year to select the influenza viruses against which the vaccine should provide protection. In fact, in just two weeks, the FDA will be convening an advisory panel of experts to help us select strains for next season’s flu vaccines. It takes several months for influenza vaccines to be produced so flu strains for the next season need to be selected even before the current flu season ends. The majority of vaccine doses are made using chicken eggs, which adds time to the production process, but some doses are made in mammalian cells or by recombinant DNA technology.
Although some factors are beyond our control, such as the ability of flu virus to change rapidly as it circulates, there are steps that we can take to ensure that the seasonal influenza vaccine protects as many individuals as possible. The FDA is collaborating with CDC, the National Institutes of Health (NIH), and other federal partners to address the full spectrum of measures that need to be taken to ensure optimal protection against the flu. These measures include working to select the most appropriate flu strains for inclusion in seasonal influenza vaccines, providing seed viruses and quality control reagents to manufacturers, and ensuring the overall quality of the manufacturing process.
During the flu season, the FDA works with the CDC, NIH, and other federal partners to see what strains are circulating and to assess the safety and effectiveness of the vaccine that is given. Using large databases covering millions of individuals, including one from the Centers for Medicare & Medicaid Services (CMS), the FDA is able to look into whether there are any unexpected findings. This information, together with surveillance information provided by the CDC, offers important insight into the selection of the next season’s vaccine strains and into whether any changes in the vaccine development process need to be made. A preliminary analysis of CMS data indicates that this year, the cell-based influenza vaccine appears to have somewhat better effectiveness in preventing influenza than the egg-based vaccine. Scientists at the FDA, CDC, and NIH are working diligently to fully understand the basis for this finding, so that all of next year’s vaccines can provide better protection in preventing the flu. Better understanding why the cell-based vaccine offered better protection against H3N2 this season, when compared to the egg-based vaccine, may offer important clues to help improve the production of a more effective H3N2 vaccine for next season.
The FDA is involved in many critical steps in the annual production of influenza vaccines. To prepare for each flu season, the FDA has a key role in selecting the strains to be included in the annual vaccine. Because there is often more than one type of influenza virus circulating each season, influenza vaccines are designed to target three or four of the most likely influenza viruses of the season: two influenza A types (H1N1 and H3N2) and one (trivalent) or two (quadrivalent) types of influenza B. In the early part of each year, the FDA, World Health Organization (WHO), CDC, NIH, and other partners collaborate by collecting and reviewing data on the circulating strains of influenza from around the world to identify those likely to cause the most illness in the upcoming season. Based upon that information and on the recommendations of the WHO - which typically meets in February to make its vaccine strain recommendations for the Northern Hemisphere - the FDA convenes its Vaccines and Related Biological Products Advisory Committee. The committee discusses the WHO recommendations but also reviews data about which flu viruses have caused illnesses in the past year, how the viruses are changing and disease trends to select the three or four flu strains that will be included in vaccines for the U.S.
Once the strains are selected, the FDA produces materials in our laboratories that are critical for making the vaccine. These include providing some manufacturers with the seed viruses used for further vaccine manufacture and the critical potency reagents needed to ensure that influenza vaccines made by one manufacturer are similar to those made by another. The FDA is also responsible for ensuring that released lots of influenza vaccines meet appropriate standards. In working to ensure vaccine quality, agency scientists have already confirmed that the genetic sequence of the influenza strains used by manufacturers to produce vaccines for this season were the same as those provided to them at the beginning of the production process. Thus, for egg-based vaccines, the lower-than-desirable efficacy being observed is not likely related to the process of adapting the virus to grow well in eggs.
Ultimately, developing a universal influenza vaccine that provides protection against many different strains of flu from year-to-year would be ideal. However, the reality of such a vaccine is likely to still be several years away. In the meantime, the FDA is collaborating with federal partners and with industry to improve the manufacturing of the current generation of influenza vaccines. In particular, our scientists are interested in looking at continuous manufacturing technologies for cell-based and recombinant vaccines, which could facilitate much more agility in responding to changes in influenza strains. It could have the potential to allow manufacturers to increase production quickly, if necessary.
During the current flu season, remember to wash your hands frequently and get vaccinated if you have not yet done so. There are still weeks of flu activity to come. People who are very sick or who are at high risk of serious flu complications who get flu symptoms should see a health care provider as soon as possible to see if they should be treated with antiviral drugs. The FDA remains committed to collaborating with other public health agencies and manufacturers to use the lessons that we are learning—and will continue to learn—from this year’s flu outbreak to prepare for the next one.
The FDA, an agency within the U.S. Department of Health and Human Services, protects the public health by assuring the safety, effectiveness, and security of human and veterinary drugs, vaccines and other biological products for human use, and medical devices. The agency also is responsible for the safety and security of our nation’s food supply, cosmetics, dietary supplements, products that give off electronic radiation, and for regulating tobacco products.
- Jennifer Dooren