The U.K. has decided to offer inoculations against Covid-19 to children aged 12 to 15 — but with just one shot of the Pfizer-BioNTech vaccine. Some may wonder why it’s not simply following what the majority of countries are doing: using the two doses that a Phase III trial has shown to have a 100% efficacy in preventing an infection. It’s not the first time the government of Prime Minister Boris Johnson has tinkered with vaccine doses. It had taken a gamble on using an extended dose interval in adults — as many as 12 weeks, in contrast to other countries, which had three weeks for the Pfizer-BioNTech vaccine and four weeks for the Moderna version.

That previous decision, of which I was initially critical, has been vindicated not only by the drop in hospitalizations and deaths, but also by the finding that an extended interval is potentially more effective in preventing infection. I believe that this latest decision on children makes a lot of sense and could be a blueprint for others to follow. 

First, a single shot is safer than two for kids. There is clear data from the U.S. Centers for Disease Control that suggests that, for 12-to-15 year olds, the risk of rare heart inflammation, referred to as myocarditis and pericarditis, associated with the Covid-19 vaccines comes mainly after the second dose of mRNA vaccines. Females had lower incidence. There is also some evidence suggesting that the Moderna shot has a potentially higher risk of heart inflammation than Pfizer-BioNTech.

Secondly, even a single shot will have efficacy. We know, from the Phase III trials of the vaccines, that one dose essentially flattened the infection curve. About ten days after the first dose of any vaccine there is already a very significant impact on infection rates in vaccinated individuals. While it is not clear how long that protection lasts for the Pfizer-BioNTech vaccine, the U.K. can rely on evidence that it has gathered from its vaccine rollout which used an eight to 12 week interval between the first and second dose of both the Pfizer-BioNTech and AstraZeneca vaccines. That showed a 55% to 70% reduction in risk of symptomatic infections for both vaccines against the alpha variant of the virus.

A single dose is also effective against the delta variant for a few months, according to data from Canada, the U.K. and Qatar, with between 58% and 76% reduction in risk of an infection. While most of this data is from adult vaccination programs, the impact on the risk of infection should not be different in a younger cohort.

Children are the least likely to be endangered by the virus. Hospitalization rates associated with a Covid-19 infection are the lowest among 12-to-15 year olds, as is mortality based on U.S. CDC data. Still, vaccinating kids will cut infection rates and help reduce the risk of longer term complications of even mild infections, including the rare, but devastating, multi-system inflammatory syndrome, which, as the name suggests, involves severe hyper-inflammation of several critical organs at the same time.

Even if the effect of one dose lasts only for a few months, it will provide meaningful cover over the winter while continuing to reduce the risk of viral transmission to other more vulnerable age groups. It will help avoid the potential of multi-virus infections with SARS-CoV-2 and other respiratory viruses. It should lead to less absenteeism and other classroom disruptions. And, perhaps the most soothing of societal benefits, parents can have a little peace of mind after months of home schooling.

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Sam Fazeli is senior pharmaceuticals analyst for Bloomberg Intelligence and director of research for EMEA.

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