New research from a team at King’s College London has found that a single dose of the Pfizer vaccine is effective in reducing the risk of COVID-19 in children.
The findings showed that one dose of vaccine also reduced the severity and duration of an infection during the Delta wave, but was much less effective at doing so for Omicron.
The study, published in the journal Lancet Regional Health, looked at data from almost 116,000 children aged 12-17, working alongside the ZOE COVID Symptom Study app.
They found a substantial and rapid reduction in infection risk after just one dose of vaccine, with the risk being 80% lower and 54% lower for Delta and Omicron respectively 14 to 30 days after the vaccine was given. What’s more, the risk was still reduced 90 days after the vaccine was given, though the protection was seen to wane for the Delta variant.
The researchers also calculated the probability that vaccinated and unvaccinated children would remain uninfected, finding that protection set in almost immediately after vaccination. However, this protection waned over time, particularly for Omicron.
Vaccinated children who had previously reported a positive COVID-19 test maintained a reinfection risk close to zero for at least 100 days during the Delta wave. The authors did not have the necessary data to make a similar assessment for Omicron. These results suggest that children will benefit from vaccination even if they had been infected with COVID-19 before.
In line with previous studies, the researchers found that COVID-19 was usually mild even in unvaccinated children, though there was also evidence that symptoms were less common in vaccinated children of all ages.
Symptoms were generally milder and duration of illness shorter with Omicron than with Delta for both vaccinated and unvaccinated children. However, several individual symptoms were less common in the younger vaccinated children, for example: anosmia, fever, low appetite, abdominal pains and muscle pain.
Currently, children aged 12-17 are eligible for two doses of the Pfizer vaccine, as are clinically vulnerable children aged 5-11. Young people aged 16-17 are eligible for an additional booster dose.
Emma Duncan, Professor of Clinical Endocrinology at King’s College London, said:
Our paper will provide useful information for parents considering vaccinating their children against SARS-CoV-2. Even a single dose of the Pfizer vaccine means children and young people are less likely to get COVID-19, and if infected post-vaccination they are likely to have a milder disease course – at least for Delta and Omicron variants. Our paper is also reassuring that Omicron in children is usually mild, even in unvaccinated children.
Dr Michael Absoud from King’s College London, said:
Our paper has implications for future policies pertaining to health resource allocation and prioritisation. Overall, a single dose of vaccination reduces COVID-19 symptoms but offers time-limited protection against infection, especially for Omicron. Our study also shows that infection acquired immunity is additionally protective. It is reassuring that children recover well post-SARS-CoV-2 infection with Delta and Omicron.