The side effects of the Pfizer-BioNTech jab against Covid-19 are likely to be mild to moderate and clear up quickly in 12-15 year olds at high risk of complications from the infection because of certain coexisting conditions, reveals a study.

While the study numbers are small, the data are representative of those teenagers most likely to benefit from the vaccination, and should offer reassurance to parents and clinicians, said researchers from the Bristol Royal Hospital for Children in the UK.

In the study, to be published in the Archives of Disease in Childhood, the researchers asked the parents of 27 children, aged between 12 and 15, to record any side effects of subsequent Covid-19 vaccinations for each child.

The children had various neurological conditions, including muscular dystrophy and cerebral palsy, plus a range of coexisting medical conditions, such as epilepsy, congenital heart defects, and immune deficiency, for which they were receiving drug treatment of various kinds.

The reported side effects were all mild to moderate, with the exception of one child who experienced severe fatigue and discomfort, combined with increased agitation. One family also reported that seizure type changed to clusters, although this had resolved a week later.

In all, there were eight 'events' in six children after the first dose, all of which resolved within 72 hours: mild rash; headache; diarrhoea; presumed sore throat; neck pain; difficulty sleeping; and low blood glucose.

After the second dose, eight additional events occurred in five children: diarrhoea; vomiting; armpit swelling; and blisters around the mouth.

Paracetamol use after the first dose was high and fever was more common than reported in studies of adults. But all recorded side effects cleared up within a week.

The UK's independent vaccine advisory group, the Joint Committee on Vaccination and Immunisation (JCVI), advised that children aged 12 and over with severe neurological disabilities, who tend to get recurrent respiratory infections and have complex care needs, should be offered the Covid-19 jab.

The only Covid jab currently authorised in the UK for under-18s is the Pfizer-BioNTech vaccine.

Countries, including the US, Canada and France, have already rolled out vaccines for people aged 12 years old and above.