Giving paracetamol to babies after vaccinations² as a precaution against fever may lower the effectiveness of the immunisation, say researchers.

研究人员称，在接种疫苗后对婴儿注射扑热息痛作为对发烧的预防措施可能降低疫苗的效力。

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Some children get a mild fever after a vaccine

A trial of 450 infants having vaccines⁴ found that paracetamol（扑热息痛） doses over the next 24 hours did indeed reduce fever.

However, the Czech researchers also found a significantly lower vaccine response with the painkiller⁵.

A UK doctor said the Lancet study backed advice not to use medicines in children without good cause.

Study leader Professor Roman Prymula said paracetamol was sometimes given prophylactically⁷ to allay（使……镇静） parents fears of high fever in children after a vaccination¹.

But the trial, which included children having routine immunisations and booster vaccines, found that the practice may actually do more harm than good.

Half of the children in the study - who were having vaccines against pneumococcal（肺炎球菌） disease, Haemophilus（嗜血杆菌） influenzae type b, diphtheria（白喉）, tetanus（破伤风）, whooping⁸ cough（百日咳）, hepatitis B（乙型肝炎）, polio（小儿麻痹症）, and rotavirus（轮状病毒） - were given three paracetamol doses every six to eight hours for the next 24 hours, while the other half did not.

It found that 42% of the children in the paracetamol group ended up having a temperature over 38C after initial vaccines, compared with 66% of children in the non-treatment group, with similar findings for booster vaccines.

But when the researchers looked at vaccine response they found lower levels of antibodies in those who had received paracetamol, suggesting the resulting immunity⁹ prompted by the vaccine was not as good.

Interferes with immunity

It is thought this is the first time such an effect has been shown and the researchers said one explanation could be that the paracetamol interferes¹⁰ with the response of immune cells to the vaccine.

"The clinical relevance¹¹ of these immunological（免疫学的） findings is unknown and needs further assessment（估价，评估）," Professor Prymula wrote.

"Prophylactic⁶ administration of [paracetamol] at the time of vaccination should nevertheless（然而，不过） no longer be routinely recommended without careful weighing of the expected benefits and risks."

Dr David Elliman, a child immunisation expert at Great Ormond Street Hospital, said he did not know how common the practice of giving paracetamol after vaccination was but he always advised parents it was unnecessary.

He added the finding about reduced immunity was very interesting and novel.

"My advice would be if the child has a fever, don't always assume it's down to the vaccine - are you happy there isn't another explanation.

"But if the child is otherwise well they probably don't have anything else wrong with them and you need to question whether they really need their fever brought down.

"Giving paracetamol before or after vaccines is not to be encouraged because firstly it has little benefit and secondly¹² this preliminary data suggests it may do harm."

A Department of Health spokeswoman said: "Some children may develop a mild fever following vaccination.

"Department of Health advice is that infant paracetamol or ibuprofen（异丁苯丙酸） can be given to a child to treat a fever.

"The findings of this study do not contradict（反驳，矛盾） this advice."