Overview

Influenza (flu) is a contagious virus that spreads throughout the U.S. all year but mainly between October–May (flu season), with a peak between December and February. Anyone can get sick with influenza, but it’s more dangerous for some people—infants, young children, people over the age of 65 years, pregnant women, and people who have certain medical conditions and/or weakened immune systems.

Since the flu virus is always changing, the flu vaccines are updated with the most current types of flu virus that are predicted to be circulating in the upcoming season. That’s why people need a flu vaccine every year for the best protection.

The seasonal flu vaccines are trivalent (current as of 2024–25 season), meaning they protect against two influenza A subtype viruses (H1N1 and H3N2) and one influenza type B virus.

Influenza virus strains were selected based on the influenza vaccine production method: egg-based, cell-based, and recombinant. People with egg allergy may receive any age-appropriate flu vaccine. The cell-based or recombinant vaccines are egg-free and may be options should someone want an egg-free vaccine.

The CDC recommends everyone aged 6 months and older get vaccinated every flu season. Children aged 6 months through 8 years may need two doses during a single flu season. Everyone else needs only one dose each flu season.

Influenza vaccines available in the U.S. market include the following:

Inactivated Influenza Vaccine (flu shot)

An inactivated influenza vaccine contains killed vaccine viruses or pieces of virus. This type of vaccine can not cause viral replication in the body and can not make you sick.

All children over the age of 6 months should get a flu vaccine every flu season. Some children between 6 months and 8 years may need two doses, but everyone will need at least one dose.

Types of flu shots:

Trivalent flu shot: This flu shot can be administered to all age groups.

Cell-based (Flucelvax): This is a flu shot grown in mammal cells instead of hen eggs and is completely egg-free. This is approved for people aged 6 months and older.

Recombinant flu shot: This vaccine is made synthetically using the virus’ genetic makeup. This vaccine is an egg-free option.

Fluzone High-dose: This vaccine has four times the amount of viral antigen (part of the vaccine that helps the body build protection) as a regular flu shot. This is approved only for people over the age of 65.

Adjuvanated (Fluad): This is made with an ingredient called an adjuvant, which helps create a stronger immune response. This is approved for people aged 65 and older.

Live, Attenuated Influenza Vaccine (LAIV): Nasal Spray – FluMist

The FluMist nasal spray flu vaccine contains weakened live flu viruses—the same viruses as other flu vaccines. It is available for administration by a healthcare provider in a clinic or pharmacy and makes for a great flu vaccine option for people with needle anxiety or phobia.

This vaccine is recommended for everyone aged 2–49 years old. LAIV is not recommended for pregnant people.

In September 2024, the FDA approved FluMist for self-administration at home for people who are aged 2–49 years old. This will be available in the 2025–26 season.

June 25–26, 2025, ACIP meeting notes on influenza vaccines

The ACIP voted 6-1 to keep the influenza vaccine recommendation for everyone 6 months and older to be vaccinated. The vaccine will include a new A/H3N2 flu virus strain and the same A/H1N1 and B/Victoria strains as we had in the flu vaccines this previous season. All vaccines will be trivalent (three strains).

The ACIP voted 5-1 (one abstained) to only use single-dose flu shots, free from the preservative thimerosal, which is used to prevent the growth of harmful bacteria and fungi—more commonly used in developing and low-income countries. Thimerosal is only found in multi-dose flu vaccine vials, not in any other vaccine in the U.S. The childhood vaccine schedule has not had a vaccine that contains thimerosal since 2001.

Thimerosal has been a target of Kennedy and the antivaccine community for decades, claiming it is a contributor to autism. Science does not support this.

Lyn Redwood, a nurse practitioner and the leader of Kennedy’s anti-vaccine group, Children’s Health Defense, presented on the topic. She called the preservative a “developmental and reproductive toxicant” that never underwent proper safety testing. The copy of her presentation was removed from the CDC website due to it citing a nonexistent study.

Redwood was recently hired by HHS as an “expert.” She delivered her presentation as a private citizen and not a representative of the federal government.

Removing the rarely-used ingredient only affects the multi-dose flu vaccines, and consumers have many choices for their flu vaccines, as is. So, it is what it is. However, the vote showed the panel’s willingness to disregard scientific data, ultimately increasing the public’s distrust in vaccines.

The vote to remove the flu vaccine containing thimerosal is concerning because the ACIP members ignored what science says to be true, and due to further distrust in vaccines, this will lead to fewer people getting vaccines, which will in turn lead to more hospitalizations and deaths.

This past season had the highest number of flu deaths since the global 2009 H1N1 flu pandemic. There have been over 250 flu deaths among children this past flu season, which ACIP member Dr. Robert Malone described as a “modest number.”

Dr. Jason Goldman, a liaison for the American College of Physicians (ACP), pushed back during the meeting, saying, “(It) is not a small number, especially if it’s your own child dying from the vaccine-preventable illness.”

Immunization schedules

Additional information about the flu vaccine

Inactivated Influenza Vaccine Information Statement

Live, Attenuated Influenza Vaccine Information Statement

CDC’s Influenza main page