Many childhood vaccines contain small amounts of aluminium to boost the immune response. Credit: Getty
When US vaccine advisers meet this week, they will turn their spotlight on little-known ingredients that are crucial to the effectiveness of many vaccines: adjuvants.
Adjuvants are compounds that boost immune responses, improving the ability of vaccines to elicit long-lasting immunity against infectious diseases. At this week’s meeting, the US Advisory Committee on Immunization Practices (ACIP) is expected to discuss aluminium, an adjuvant widely used in inoculations against diphtheria, tetanus and hepatitis B, among others. Over the past century, hundreds of millions of people have received vaccines containing small amounts of aluminium as an adjuvant.
But researchers are also racing to develop new adjuvants that can stimulate the immune responses needed to combat specific pathogens. Such adjuvants could prove crucial to the success of the next generation of vaccines against diseases including tuberculosis and malaria, and against viruses such as HIV, says Darrell Irvine, a vaccine immunologist at the Scripps Research Institute in La Jolla, California.
“These are huge global health issues,” he says. “And adjuvants are likely going to be part of the solution.”
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Adjuvants can work in different ways. Some adjuvants trigger low levels of inflammation at the injection site, thereby boosting recruitment of immune cells to where they are needed and encouraging the cells to linger there. Others are more specific, activating molecular signalling pathways in certain classes of immune cells.
Aluminium is in the first category, and its vaccine-boosting properties have been known for more than a century, says Irvine. Decades of use and scrutiny by regulators have clearly established that the benefits of using aluminium adjuvants outweigh any potential risks, says Marco Cavaleri, head of public-health threats at the European Medicines Agency in Amsterdam, Netherlands.
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Even so, US health secretary Robert F. Kennedy Jr, who has long campaigned against vaccines, has argued that aluminium adjuvants are linked to autism and food allergies. In July, researchers in Denmark published a study of more than one million children that found no such link1. Kennedy called for the study to be retracted; the journal declined.
The ACIP advisers, handpicked by Kennedy, will discuss the use of aluminium in vaccines this week, but they have not yet scheduled a vote. Any requirement to eliminate aluminium would be a shock to the system, says Cavaleri, and would render some crucial vaccines ineffective. “You cannot just get rid of an adjuvant that works and is safe before you have something else that you know will be a good replacement,” he says.
