Paracetamol affects childhood jabs

Friday October 16 2009

Giving paracetamol to babies after routine vaccine jabs may lessen the effectiveness of the immunisation, according to BBC News.

The study behind this coverage is an important and well-conducted trial in which 459 babies receiving their immunisations were either routinely given paracetamol in the 24 hours following their injection or were given none. Although the drug was clearly successful in reducing the risk of a fever developing, it was shown to reduce the immune response to the vaccine, suggesting that it would be less effective. However, although the preventative use of paracetamol had an effect on immune response, using the drug to lower existing fever did not.

This means that parents should not be concerned about giving paracetamol to their child to treat a raised temperature or associated symptoms of pain and irritability. But if a baby has just had an immunisation, it may be wise only to give them paracetamol if they are unwell, and not to prevent symptoms from occurring.

Where did the story come from?

This research was conducted by Roman Prymula and colleagues from the University of Defence in the Czech Republic and other European institutions. The study was funded by the vaccine manufacturer GlaxoSmithKline Biologicals and published in the peer-reviewed medical journal The Lancet.

What kind of scientific study was this?

This was a Phase III randomised, controlled trial conducted to look at the effect of giving paracetamol to babies during and immediately following vaccination. Paracetamol is sometimes given to an infant to decrease their risk of developing a fever or having a fit caused by a fever (a febrile convulsion).

The main outcome of interest was any reduction of fevers above 38°C in the group that received paracetamol compared to the group that did not. The secondary outcome studied was the immune response following the vaccine. The study looked at a number of vaccines used in routine immunisations, including those against:

  • haemophilus influenza,
  • diphtheria,
  • tetanus and pertussis,
  • polio, and
  • hepatitis B.

The researchers enrolled 459 infants aged between nine and 16 weeks from medical centres in the Czech Republic between September 2006 and April 2007. The trial was conducted in two parts. The first focused on the primary vaccination schedule when the infant was three to five months old, while the second looked at booster vaccinations when the baby was 12 to 15 months old.

The babies were randomly chosen to receive either paracetamol administered every six to eight hours during the 24 hours following the vaccination, or to receive no paracetamol treatment. This meant the trial was “unblinded”, which means that the parents knew whether their baby was receiving paracetamol or not. Babies were kept in the same treatment group for the booster vaccinations, so if they received paracetamol for their primary vaccinations they received it again for their booster.

While the study was still underway, early results indicated that paracetamol had an effect on the immune response, and so any paracetamol treatment was withdrawn. By the time this became apparent, some of the babies randomised to receive paracetamol had already received a booster vaccine dose combined with paracetamol, but following these results no further babies received paracetamol a second time.

What were the results of the study?

In both groups, a fever of 39.5°C or greater was rare following vaccination:

  • <1% in the paracetamol-treated group at primary immunisation,
  • 1 % in the untreated group at primary immunisation,
  • 2% the paracetamol-treated group after the booster, and
  • 1% the paracetamol-treated group after the booster.

However, there was a lower proportion of babies with temperatures of 38°C or greater among the paracetamol-treated group:

  • 42% (94/226 babies) in the paracetamol-treated group at primary immunisation,
  • 66% (154/233 babies) in the untreated group at primary immunisation,
  • 36% (64/178 babies) of the paracetamol-treated group after the booster, and
  • 58% (100/172 babies) the paracetamol-treated group after the booster.

After the primary vaccine doses, 64 doses of paracetamol also had to be given in the group who were not randomised to receive paracetamol. Paracetamol-treated infants also had fewer parental-reported symptoms, such as pain and irritability.

For most of the bacterial and viral vaccine components the antibody concentrations achieved following the primary immunisations were significantly lower in the paracetamol-treated group than in the group who did not receive paracetamol. The response varied depending on the vaccination type given, as not all vaccine responses were equally affected by prophylactic paracetamol.

What interpretations did the researchers draw from these results?

The researchers concluded that although feverish reactions were significantly decreased by the use of paracetamol, prophylactic (preventative) administration of antipyretic drugs (to prevent fever) at the time of vaccination should not be routinely recommended due to the reduced antibody response to the vaccine.

What does the NHS Knowledge Service make of this study?

This is an important and well-conducted trial. It has found that routinely giving a baby paracetamol in the 24 hours following their childhood immunisations, although clearly successful in reducing the risk of fever developing, reduces the immune response to the vaccine. This suggests that the vaccination will be less effective.

Other key points to note:

  • There was no reduction in immunity following just a single dose of paracetamol or the use of paracetamol to treat a developed fever. It was only the regular use of preventative paracetamol use that was associated with decreased immune response. On this basis, parents should not be concerned about giving paracetamol to their baby/child to treat a raised temperature or associated symptoms of pain and irritability.
  • In both treatment groups, high temperatures of above 39.5°C and the need to seek medical attention for an immunisation reaction were both uncommon.
  • As the researchers say, there have been very few published studies on the effect of antipyretic (anti-fever) medications on child immunisation responses. The reason for the observed immune response following paracetamol is unclear. Whether this may be due to paracetamol preventing the inflammatory reactions that lead to the development of antibodies is one theory.
    It is unclear why all vaccine responses were not equally affected. This uncertainty has implications for the upcoming swine-flu vaccination programme, as this study was unable to demonstrate whether the immunity offered by influenza vaccination might be reduced by paracetamol. Much further research is needed to answer this question.

However, it may be wise at the current time only to give your baby paracetamol following immunisation if they develop a temperature or feel unwell, and not to give it routinely as a preventative measure.

Analysis by Bazian
Edited by NHS Website