September 27, 2018
This week marks the official start of “flu season” for 2018-2019. The FDA, along with its partners across the Department of Health and Human Services, has been working throughout the year to prepare the development of a safe, effective flu vaccine for the season. I got my flu shot this week at an
along with the U.S. Surgeon General Jerome M. Adams. With the severity of last year’s flu season, I know that there are questions about the effectiveness and benefits of the flu vaccine. I want to take this opportunity to update you on what we’ve learned from last season, the steps we’re taking to improve our readiness and the effectiveness of this coming year’s flu vaccine, and the continued importance of getting vaccinated.
While the effectiveness of the vaccine may vary year to year, I want to assure you that evidence remains strong to support the benefits of the annual flu vaccine for most people. Though flu season is generally thought of as starting in September, we at the FDA work year-round to prepare for each flu season. And we’re committed to working together with the scientific and medical communities to better protect the public against the flu and apply lessons learned to improve vaccine effectiveness each year.
The FDA has a key role in selecting the strains to be included in seasonal flu vaccines. Because there’s often more than one type of influenza virus circulating each season, influenza vaccines are designed to target three or four of the influenza viruses that are most likely to circulate during the season: two influenza A types (H1N1 and H3N2) and one (trivalent formulation) or two (quadrivalent formulation) types of influenza B.
One of the challenges in fighting flu is that the viruses can change their genetic make-up rapidly -- not only between flu seasons, but also during the course of a single season. As a result, the seasonal influenza vaccine needs to be evaluated annually to see whether its composition needs to be adjusted.
This evaluation is based on the influenza viruses, or strains, that are expected to be in circulation during the upcoming influenza season. The need to evaluate and potentially change the vaccine strains is unique to the influenza vaccine, as the composition of antigens included in other preventive vaccines doesn’t change. To select the influenza virus strains for inclusion in each season’s flu vaccine, the FDA, World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC) and other partners review data collected on the circulating strains of influenza from around the world to identify those strains that are most likely to cause the most illness during the U.S. flu season. Since it generally takes several months for influenza vaccines to be produced, flu strains for the next season need to be selected months in advance to ensure we’re prepared with enough supply when flu season hits. Our advisory committee met in March 2018 to select the strains for this upcoming season.
Last year’s flu vaccine was less protective than it had been in many previous years. In part, this was because the vaccine was not as effective against one of the predominant circulating strains of influenza. That circulating strain of influenza was contained in the vaccine. In other words, we guessed right about the common strains that dominated last year’s flu season. The problem was that the “seed” influenza strain that was used to produce the vaccines had changed in some subtle but meaningful ways. It’s now believed that part of the reason that the vaccine was not as protective is that the flu strain used to manufacture the vaccine mutated very subtly during the development process. The result of these small, but very targeted changes, was that the protective immune “antibodies” that the flu vaccine elicited were slightly different than what people needed to mount the most effective immune response to the virus.
This isn’t the first time that the vaccine strains have deviated in some important ways from the influenza strain that ends up circulating during the flu season. But we’ve learned a lot of lessons from these highly unfortunate incidents. And we’ve improved our scientific methods to reduce the odds that it happens again.
We’ve worked closely with our colleagues at the CDC and other agencies to ensure that as many of the potential issues with last year’s vaccine as possible were addressed this year. This includes replacement of the influenza A H3N2 strain used in 2017-2018 (A Hong Kong) with a new strain (A Singapore) that will hopefully be a better match for the circulating strains in 2018-2019. One of the 2017-2018 influenza B strains (B/Brisbane) has also been replaced for 2018-2019 with a potentially better match as well (B/Colorado). We’ll keep working with our partners develop vaccines that more protective against flu.
We have some confidence, based on the pattern of influenza circulating now in the Southern hemisphere, that the flu strains chosen for this year’s U.S. seasonal flu vaccine should offer Americans good protection.
A seasonal flu vaccine is one of the most effective and safest ways to protect yourself, your family and your community from the flu and serious flu-related complications, which can result in hospitalizations. Flu vaccines work by preparing the body’s immune system when exposed to multiple strains of influenza viruses circulating during the influenza season. When a person gets vaccinated, their body’s immune system is able to recognize and respond to a future exposure of the disease-causing agent to prevent that disease. The FDA and CDC recommend that most individuals 6 months of age and older should get the influenza vaccine every year to protect against the flu and flu-related health complications. It’s especially important for people in high-risk groups, such as seniors, pregnant women, and young children, as well as people who are in close contact with those at high risk to get an influenza vaccine every year as recommended by CDC’s Advisory Committee on Immunization Practices (ACIP). In fact, last year, tragically most of the children who died of flu had not received the influenza vaccine. It’s important to note that even when the vaccine does not fully prevent someone from contracting flu, it may lessen its severity.
So how did we make the decisions regarding this year’s flu vaccine?
Typically, the FDA convenes its Vaccines and Related Biological Products Advisory Committee (VRBPAC) in early winter to select strains for the next flu season. To select the three or four flu strains that will be included in vaccines, the committee discusses the WHO recommendations, and reviews data about which flu viruses have caused illnesses in the past year, how the viruses are changing and disease trends. Since it generally takes several months for influenza vaccines to be produced, flu strains for the next season need to be selected months in advance. After the strains are selected, vaccine manufacturers begin to actively prepare their vaccine for the upcoming flu season. During manufacturing, the influenza virus strains are combined to formulate the vaccine into standard dosages. The vaccine is then filled into vials, syringes and, for the nasal vaccine, sprayers. Regardless of the dosage, the manufacturing method, or whether they are trivalent or quadrivalent, all licensed flu vaccines have been evaluated by the FDA and determined to be safe and effective.
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 reagents needed to test the vaccine for potency and identity (to ensure standardization). The FDA is also responsible for ensuring that released lots of influenza vaccines meet appropriate standards. Each vaccine undergoes quality control tests, including testing for sterility. Manufacturers submit the results of their testing, along with sample vials from each lot to the FDA for "lot release." The FDA typically begins releasing lots of flu vaccines in late summer and lot release can continue into early fall.
Once lots are released, manufacturers distribute vaccine throughout the United States for use by the public.
The FDA works closely with the CDC, the National Institutes of Health, and other federal partners not only to monitor what strains are circulating, but also to look at new ways of collecting and tracking data on flu vaccine effectiveness and to better understand the potential impacts of different vaccine development processes on effectiveness. By looking closely at the available data and identifying data gaps to potentially address in future flu seasons, we believe that we have the greatest chance of developing vaccines that even more effectively prevent the flu in the future. Moreover, while CDC provides immunization recommendations, the FDA and CDC collaborate each influenza season to monitor the safety and effectiveness of all influenza vaccines.
Part of the complexity and challenges of how vaccines are developed relates to how they’re manufactured. Most of the flu vaccines are still made using chicken eggs. This is an old, and very safe method. Because of its safety, its wide use, and our long experience with these tools, there’s reluctance to move away from this approach despite availability of new technology that offers certain advantages.
While the majority of vaccine doses are made using chicken eggs, some doses are made in mammalian cells or by recombinant DNA technology. The latter two are some of the newer technologies. We found that a preliminary analysis of Centers for Medicare and Medicaid Services data indicates that for the 2017-2018 flu season, the cell-based influenza vaccine appeared to have somewhat better effectiveness in preventing influenza than the egg-based vaccine. Scientists across federal agencies are hoping that this data can help offer important clues to help improve the production of effective vaccines for future flu seasons. One theory may be that the genetic adaptations to the flu strain “seed stock” that was required to enable that influenza strain to grow efficiently in the chicken eggs also introduced certain genetic changes to that strain that made it less effective at producing fully protecting vaccines. However, this is just one theory. More data is needed to better understand these preliminary findings.
The FDA is encouraging steps that we can take now and in the near future to invest in advanced domestic manufacturing to ensure new and existing technologies are scalable so that manufacturers can meet domestic and global demand. For example, the FDA is working to facilitate development of more effective cell lines that can be better scaled through advanced manufacturing technologies and ways that a more robust recombinant vaccine manufacturing process could be developed to increase yield, while reducing cost. Advanced manufacturing technologies hold great promise for both cell-based and recombinant influenza vaccines, because supply could be more easily ramped up on short notice and may be better suited to adapt if changes in flu strains are identified during a flu season.
Once again, it is important to note the potential benefits of the flu vaccine. The CDC’s data on vaccine effectiveness show that if vaccinated individuals did become ill with the flu last year, they were much less likely to be hospitalized or face serious complications compared to people who had not been vaccinated. These data are consistent with previous influenza seasons. The flu vaccine remains one of the most important interventions that most people can pursue to help reduce their chances of serious illness.
As we prepare for flu season, I want to assure you that efforts for the 2018-2019 flu vaccine are well underway. The FDA has already evaluated and released many vaccine lots and influenza vaccine is available now from healthcare providers. Providers are starting to administer these vaccines. Additional lots will be released throughout the season. I encourage you to speak to your health care provider about steps that you and your family can take to protect against the flu, including an annual flu shot.
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.