What you need to know about mRNA vaccines in light of RFK’s claims

The US health secretary claimed mRNA vaccines are ineffective against respiratory diseases, while announcing he was cutting half a billion dollars in funding for mRNA vaccine development. But this goes against the scientific evidence we have, which shows many mRNA vaccines work as well as – or better than – other types of vaccine. Here is what you need to know to assess these claims.

In announcing the cuts, the head of the US Department of Health and Human Services, Robert F Kennedy Jr, claimed  “these vaccines fail to protect effectively against upper respiratory infections like COVID and flu”. Kennedy said the agency would shift funding “toward safer, broader vaccine platforms that remain effective even as viruses mutate”.

There is now a wide range of vaccine types: live viruses, killed viruses, genetically engineered viral shells, single viral proteins and mRNAs coding for viral proteins. The effectiveness of all of these kinds of vaccines often has a lot more to do with the nature of the virus being targeted than the vaccine itself.

For instance, the MMR vaccine can be 100 per cent effective at preventing measles outbreaks if more than about 90 per cent of a population is vaccinated. But the measles virus is an easy target because it does not change much and it takes a convoluted route deep inside the body, meaning there are plenty of opportunities for the immune system to intercept it before people develop symptoms or become infectious.

In contrast, the respiratory viruses that cause colds and flus first infect the cells lining the nose and throat. It is hard to generate high levels of effective antibodies in these membranes, so it is much more difficult to prevent infections and onward transmission than with measles.

Additionally, cold, flu and covid-19 viruses are constantly mutating, and there is strong evolutionary selection for any mutations that help a virus dodge the immune protection generated by infections or vaccinations. For this reason, no flu or covid-19 vaccine of any type provides the same lifelong protection as the measles component of the MMR vaccine. But the mRNA ones do work relatively well.

For instance, some mRNA covid-19 vaccines were more than 90 per cent effective against symptomatic infections, with even higher protection against severe disease. For comparison, the effectiveness of the non-mRNA vaccines used to protect from the annual flu varies from 20 to 60 per cent. And in a recent trial, a combined covid-flu mRNA vaccine outperformed existing, non-mRNA flu vaccines in people aged over 50 – those who most need protection.

So Kennedy’s claim of a lack of efficacy is nonsense. This is not to say mRNA vaccines are always better than other types. But new vaccines have to outperform older ones in trials – mRNA shots won’t get approved if they are not better.

Kennedy also claims other kinds of vaccines are more likely to remain effective as viruses mutate. This seems to be a reference to developing “universal vaccines” – a single vaccine that is effective against all flu viruses, say, or one that works against all coronaviruses. The idea is to target the outer parts of viruses that don’t change. But this is hard to do because viruses tend to hide their unchanging parts under the parts that do change.

Efforts to develop effective universal vaccines have so far failed, despite decades of efforts, so focusing too much funding on them could be a mistake. What is more, mRNA technology can, and already has, been used to create experimental universal vaccines. So the second part of Kennedy’s statement is also nonsense.

Last but not least, efficacy isn’t everything. Safety, cost and the speed of vaccine development are crucial, too. Here mRNA technology has some huge advantages. It is safer than vaccines consisting of actual viruses, cheaper than vaccines consisting of a single viral protein and can be developed much faster than either type – which is important with fast-changing respiratory viruses, especially in a pandemic situation.

In addition, the technology in mRNA vaccines could be used more broadly to develop a huge range of other treatments. The funding cuts announced by Kennedy on the basis of his false claim could slow development by deterring companies from investing in this approach.