How vaccine recommendations have changed in the US

On 26 June, the US Advisory Committee on Immunization Practices (ACIP) rolled back recommendations for flu shots containing a rare preservative falsely linked to autism. While the move is unlikely to affect vaccine access, it exemplifies the US government’s wider effort to upend the vaccine recommendation process.

What is the ACIP and how has it changed?

The ACIP is a group of experts who advise the US Centers for Disease Control and Prevention (CDC) on vaccine recommendations. It was established in 1964, and its members are appointed by the Secretary of Health and Human Services, currently Robert F Kennedy Jr – a long-time vaccine sceptic.

Kennedy abruptly laid off all 17 members of the ACIP in early June, saying that he did so to reduce conflicts of interest. “A clean sweep is necessary to reestablish public confidence in vaccine science,” said Kennedy in a press release.

Some public health experts have pushed back. “I had confidence in the ACIP before Kennedy did [this]. Now I have zero,” says Amesh Adalja at Johns Hopkins University in Maryland. “Unilaterally removing an entire panel of experts is reckless, shortsighted and severely harmful,” said Tina Tan, president of the Infectious Diseases Society of America in a statement.

Kennedy appointed eight new members – though one stepped down before the first meeting of the new panel. Many of the members have previously expressed concerns about some vaccines. For instance, Robert Malone, who helped formulate mRNA-based vaccine technology, suggested on The Joe Rogan Experience podcast in 2021 that covid-19 vaccines may be causing heart attacks and strokes. A 2024 study of nearly 46 million adults found lower rates of heart attack and stroke after covid-19 vaccination, yet higher incidences of some rare conditions, such as myocarditis and pericarditis.

A spokesperson for the CDC says: “Dr. Malone is a seasoned physician who believes in rigorous, evidence-based review, not blind endorsement. Questioning flawed policies or demanding better data doesn’t make someone anti-vaccine, it makes them a responsible expert more than qualified to serve on the ACIP committee.”

Adalja says some of the other members appear to have no significant expertise on vaccines, infectious diseases or epidemiology. “So, no. I don’t think [Kennedy] has increased trust. He’s actually made the ACIP an irrelevant organisation,” he says.

What vaccine recommendations have changed?

In May, Kennedy announced via a video on the social media platform X that the CDC would stop recommending covid-19 vaccines for most children and pregnancies. The decision was made without ACIP input, breaking decades of precedent.

The CDC has since updated its immunisation guidelines for children and adolescents,  recommending a decision on covid-19 vaccination be made after speaking with a healthcare provider and based on personal preference.

The new ACIP panel also voted to stop recommending influenza vaccines containing thimerosal, a preservative used in some vaccines, during its first meeting. The panel also voted to recommend seasonal flu shots for everyone 6 months of age and older.

What is thimerosal and is it safe?

Thimerosal is in some vaccines to prevent bacterial contamination. It contains a small amount of mercury, which is metabolised into a by-product called ethyl mercury.

Ethyl mercury is distinct from the highly toxic compound methyl mercury, which is found in the environment and certain foods, like fish. While methyl mercury is highly toxic and can accumulate in the body, numerous studies have shown low doses of ethyl mercury are safe. It is also cleared from the blood within 30 days, even in small babies.

Anti-vaccine groups have falsely claimed thimerosal causes autism, although no studies have established such a link. For instance, a 2014 study of nearly 1.3 million children showed no relationship between vaccination, including with thimerosal vaccines, and autism.

The US Food and Drug Administration (FDA) conducted a comprehensive review of thimerosal in childhood vaccines in 1999 and identified no side effects other than minor allergic reactions at the injection site.

Which vaccines contain thimerosal?

Use of thimerosal in vaccines has declined over time as formulations have changed and vaccines have shifted to being distributed in single-dose containers, so there is less chance of introducing bacteria to the vials.

No routine childhood immunisation contains thimerosal, with the exception of some flu shots, but these vaccines are used sparingly. For instance, only 3 per cent of children and 2 per cent of adults 65 years and older received flu vaccines containing thimerosal in the 2024-2025 flu season.

How does new US vaccine policy compare with that of other countries?

Other countries have recommended against thimerosal vaccines. For instance, the UK removed thimerosal from routine immunisations between 2003 and 2005 as a precautionary measure aimed at reducing mercury exposure from all sources. Still, the government found no evidence of harm and has deployed some vaccines that contain thimerosal, such as one targeting H1N1, during select flu seasons.

In 1999, the European Medicines Agency (EMA) promoted the use of vaccines without thimerosal despite finding no evidence of harm. It updated its guidance in 2004 after new data reaffirmed the preservative’s safety, noting that “the benefits of vaccination far outweigh the risks, if any of exposure to thimerosal-containing vaccines.” The organisation reviewed the guidelines again in 2016 and found they are still relevant.

Will I be able to get a vaccine for myself or my child?

Given that most seasonal flu shots don’t contain thimerosal, it is unlikely that the ACIP’s recommendation will affect vaccines access. The CDC’s updated guidance on covid-19 vaccines in children and during pregnancy shouldn’t affect vaccine availability either.