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NSAIDs inhibit COX-2, which is produced by B cells. As well as easing pain, blocking COX-2 hinders B-cell production of neutralising antibodies after vaccination.   

This could mean that the immune system fails to mount a sufficient response against the anti- gen to protect against future infection, claim the researchers.  

The theory is based on studies into a vaccine against human papillomavirus (HPV) 16. Mouse studies showed that animals engineered to lack COX-2 produced 10-fold fewer neutralising antibodies after vaccination than control mice.  

Preserved blood samples from clinical trial volunteers vaccinated against HPV-16 were also tested. When the B cells were reactivated they produced fewer antibodies to HPV 16 after treatment with a COX-2 inhibitor.  

The findings could apply to other vaccines and could be a concern in elderly people receiving annual flu vaccines, say the researchers.  

Dr Nigel Higson, a Brighton GP with an interest in virology, said that, although the link was theoretical, GPs should delay vaccinations if patients were taking a short course of NSAIDs.  

‘This study demonstrates a concern. We should only vaccinate when the patient is well,’ he said.  

Berkshire GP and RCGP immunisation spokesman Dr George Kassianos said more research was needed to see whether all vaccines were affected.  

‘If it relates to other vaccines, including the influenza vaccine, the effect should be small,’ he said. ‘For some time now we have been decreasing prescribing of COX-2 inhibitors in view of their reported cardiac adverse effects.