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What is the Flu: Symptoms, Treatments and Vaccines


Influenza, or the flu, is a threat to global health worldwide with an estimated 1 billion cases every year.1

Seasonal flu vaccines are approved for use in most populations, but leave room for improvement, as they typically provide 40 percent to 60 percent protection against circulating flu strains.2

  • What is the Flu?

    Seasonal flu is a respiratory infection caused by the flu virus.3

  • Who Gets the Flu and How?

    Flu results in an estimated 1 billion cases every year, including approximately 5 million cases of severe illness and 290,000 to up to 650,000 deaths worldwide.4,5

    Flu spreads easily and can lead to serious complications for people with weakened immune systems, certain chronic medical conditions, older people, young children, and pregnant women.6

  • What are the Signs and Symptoms of the Flu?

    Flu can result in mild to severe illness with symptoms including:

    • Fever
    • Cough
    • Headache
    • Muscle and body aches
    • Sore throat
    • Tiredness
    • Runny or stuffy nose7
  • How is the Flu Diagnosed?

    Flu cannot be diagnosed based on symptoms alone. For a diagnosis to be confirmed, laboratory tests are used to detect flu viruses.8

  • Can the Flu be Prevented or Treated?

    Many flu vaccines are already available, but flu remains an area of critical need for public health globally. New potential flu vaccine options are in development that may increase how effective they are at helping prevent flu and ultimately improve future public health outcomes. In the meantime, annual vaccination with approved flu vaccines is recommended by the CDC for everyone 6 months and older (with rare exceptions).9

    Antiviral drugs are prescription medicines available to treat flu and are most effective if started early.10 They are not sold over the counter and require a prescription from a healthcare provider.

    Pfizer has initiated its first program leveraging mRNA technology for a potential next generation flu vaccine. mRNA’s flexibility and rapid manufacturing could potentially transform global health outcomes for the illness.

  • Why is a Potential mRNA Vaccine for Flu Being Studied?

    There is a clear need for flu vaccines with better strain coverage and that mRNA flu technology may be the right tool to take on this challenge. Also, due to the technology’s flexibility there is the potential for rapid and reliable manufacturing.

    Pfizer’s Phase 1 study of mRNA flu vaccine candidates is now underway. The study is evaluating the safety, tolerability, and immunogenicity (ability to causes an immune response in the body) of a single dose quadrivalent mRNA vaccine against flu.

  • What is the Difference Between Conventional Flu Vaccines and Potential mRNA-based Vaccines?

    A key difference is speed. The development process for conventional flu vaccines takes many months. First, the viruses are grown (typically in chicken eggs or cells from a mammal), then inactivated and processed to be made into a vaccine. This process faces multiple challenges and can impact how well any season’s vaccines are matched to those that are the predominant strains. For example, traditionally vaccine strains to be grown are chosen more than six months before the start of the flu season that they target in the Northern or Southern Hemisphere. During that time, the common circulating flu strain(s) can change, but by then, it is too late to re-start the process.

    Because mRNA technology is different, utilizing synthetic RNA instead of inactivated viruses, a successfully developed mRNA-based flu vaccine should allow for flexibility to rapidly and reliably identify and manufacture a flu vaccine that closely matches the strains in circulation in any given season.

  • How Will Efficiency in mRNA Vaccine Production Impact the Potential mRNA Flu Vaccine?

    Utilizing mRNA technology will likely speed the vaccine development process and could decrease flu vaccine manufacturing time for new strains by a month or more. Having more time to identify the ideal flu strains to provide better strain coverage and improved efficacy in flu vaccines could help protect more lives around the world.

  • What’s Next for Pfizer’s mRNA Program?

    We think that there is potential for significant scientific opportunity in mRNA technology. Pfizer will continue to build on its leadership in leveraging the technology through the flu vaccine development program. Beyond the flu, Pfizer plans to expand its research to investigate the application of mRNA technology for other respiratory viruses, cancer, and genetic diseases.

1WHO Launches new global influenza strategy. WHO. Available at
2Vaccine Effectiveness: How Well do the Flu Vaccines Work? CDC. Available at
3Influenza (Seasonal). World Health Organization. Available at
4WHO Launches new global influenza strategy. WHO. Available at
5Influenza (Seasonal). World Health Organization. Available at
6Key Facts About Influenza (Flu). CDC. Available at
7Key Facts About Influenza (Flu). CDC. Available at
8Diagnosing Flu. CDC. Available at
9Frequently Asked Influenza (Flu) Questions: 2021-2022 Season. CDC. Available at
10What You Should Know About Flu Antiviral Drugs. CDC. Available at