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鈥檚 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 鈥� 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. 鈥淎 clean sweep is necessary to reestablish public confidence in vaccine science,鈥� said Kennedy in a .

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

Kennedy appointed eight new members 鈥� 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 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: 鈥淒r. Malone is a seasoned physician who believes in rigorous, evidence-based review, not blind endorsement. Questioning flawed policies or demanding better data doesn鈥檛 make someone anti-vaccine, it makes them a responsible expert more than qualified to serve on the ACIP committee.鈥�

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Adalja says some of the other members appear to have no significant expertise on vaccines, infectious diseases or epidemiology. 鈥淪o, no. I don鈥檛 think [Kennedy] has increased trust. He鈥檚 actually made the ACIP an irrelevant organisation,鈥� 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 , 聽recommending a decision on covid-19 vaccination be made after speaking with a healthcare provider and .

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, have shown low doses of are safe. It is also , even in small babies.

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

The US (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 .

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

Other countries have recommended against thimerosal vaccines. For instance, the 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 (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鈥檚 safety, noting that 鈥渢he benefits of vaccination far outweigh the risks, if any of exposure to thimerosal-containing vaccines.鈥� 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鈥檛 contain thimerosal, it is unlikely that the ACIP鈥檚 recommendation will affect vaccines access. The CDC鈥檚 updated guidance on covid-19 vaccines in children and during pregnancy shouldn鈥檛 affect vaccine availability either.

Deaths from heart attacks have plummeted in the US over the past 50 years, whereas deaths from chronic heart conditions have skyrocketed, probably due to people living longer.

鈥淲e鈥檝e made some really great progress in certain areas of heart disease mortality, but now we鈥檙e seeing this shift,鈥� says at Stanford University in California.

She and her colleagues collected data on heart disease deaths from 1970 to 2022 using the US Centers for Disease Control and Prevention鈥檚 WONDER database, which tracks all recorded fatalities in the country.

They found that in 2022, heart disease accounted for 24 per cent of all deaths in the US, down from 41 per cent in 1970. The decline is largely thanks to an almost 90 per cent decrease in heart attack deaths, which were once the deadliest form of heart disease.

鈥淚ncredible progress has been made to reduce deaths from heart attacks over the last 50 years,鈥� says King. This includes new therapies such as heart stents, coronary artery bypass surgery and cholesterol-lowering medications. Public health measures, such as bystander CPR training and efforts to lower smoking rates, have also probably helped, says King.

Even so, heart disease remains the country鈥檚 top killer, mainly because deaths from other types of heart disease 鈥� mostly chronic conditions 鈥� have increased 81 per cent over the same period. For instance, fatalities from heart failure, arrhythmia and hypertensive heart disease have risen 146 per cent, 106 per cent and 450 per cent, respectively.

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鈥淎 lot of these conditions are conditions that come with age,鈥� says King. 鈥淭o us, it seems like people that are now surviving these heart attacks are living longer and having more time to sort of develop these chronic heart conditions.鈥�

However, the data may exaggerate the shift in heart disease deaths. 鈥淭here are a lot of different causes that could lead to somebody鈥檚 death, and that can lead to misclassification or oversimplification,鈥� says King. For instance, many people die from heart failure after having survived a heart attack. 鈥淭he underlying cause of that heart failure is still the blockages in those coronary arteries, so it isn鈥檛 black and white,鈥� says King.

Still, the majority of heart disease deaths are clearly no longer due to heart attacks. 鈥淚t is going to be important that we focus on these other rising causes of mortality,鈥� says King. 鈥淔inding ways to age healthily will be the next frontier in cardiology.鈥�