The US took the unprecedented step of dropping the number of vaccines it recommends for every child, leaving other immunisations, such as flu shots, open to families to choose, but without clear guidance.

Officials said on Monday that the overhaul to the federal vaccine schedule won't result in any families losing access or insurance coverage for vaccines, but medical experts slammed the move, saying it could lead to reduced uptake of important vaccinations and increase disease.

The change came after President Donald Trump, in December, asked the US Department of Health and Human Services to review how peer nations approach vaccine recommendations and consider revising the US schedule to align with their guidance.

Acting CDC Director Jim O'Neill approved the updated guidelines, the Department of Health and Human Services said on Monday. The move was outside the typical process for vaccine recommendations in which an outside panel of expert advisers to the Centers for Disease Control and Prevention considers the merits of each vaccine with an eye toward public health.

The US dropped its recommendation for rotavirus, influenza, meningococcal disease, and hepatitis A, and said parents should consult healthcare providers under what it calls shared clinical-decision-making.

'Decisions should be based on evidence, not comparisons'

Dr Sean O'Leary, chair of the American Academy of Paediatrics, said that other developed countries face different disease risks and have different healthcare systems than the United States. Unlike the US, which depends on private healthcare, most countries provide basic universal healthcare that is paid for by the government.

"Any decision about the US childhood vaccination schedule should be grounded in evidence, transparency and established scientific processes, not comparisons that overlook critical differences between countries or health systems," he said.

The vaccine schedules of the 20 reviewed countries show that the flu shot is recommended universally in 4 countries, and a shot against hepatitis A is universal only in Greece. The rotavirus shot is recommended for all children in 17 countries, and shots against meningococcal disease are recommended in 16 of the countries.

The updated recommendations maintain immunisations for 11 diseases, including measles, mumps, and varicella, while categorising others as either targeted for high-risk groups or subject to the shared-decision-making category, HHS said.

Insurance providers will continue covering immunisation costs regardless of the category, senior HHS officials told reporters on a call. Among the changes, the CDC now recommends a single dose of the human papillomavirus vaccine instead of two.