Three new studies provide an initial look at how well some of the most widely used COVID-19 vaccines are at protecting young children from the coronavirus1–3. The findings – including data from young children under the age of three – have prompted mixed reactions among researchers about whether the use of vaccines should be recommended in children.
The research examines two “disabled” vaccines, based on whole, killed viruses, developed by Chinese scientists. The results, from Argentina, Brazil and Chile, show that, in children, vaccines offer little protection against SARS-CoV-2 infection and modest protection against COVID-19 symptoms. Studies also show that the vaccines are less effective against the now-prevalent Omicron variant than the previous Delta variant. The studies have not yet been peer-reviewed.
The findings prompted some scientists to argue that the two vaccines should be used to protect children, especially since the inactivated virus technology has a long safety record in common vaccines given to infants for polio and influenza. “It’s important to get children vaccinated to avoid severe cases,” says Ini Cruz, an epidemiologist at the London School of Hygiene and Tropical Medicine and a co-author of one of the studies.3.
But others note that severe illness and death from COVID-19 is rare in children, and vaccines do not provide great protection against SARS-CoV-2 infection or mild illness. Many children, including in well-resourced places like the United States, have had the virus at least once and may already have acquired some immunity, says Shabbir Madi, a vaccinologist at the University of the Witwatersrand in South Africa. He says the vaccine data “does not support the case for universal vaccination of young children”.
The new studies provide data on two of the world’s most used COVID-19 vaccines in adults – CoronaVac, made by Beijing-based Sinovac, and one made by Beijing-based state-owned Sinopharm. More than 5 billion doses of vaccines have been administered worldwide, according to health analytics company Airfinity in London and the non-profit organization Our World in Data in Oxford, UK. This total includes several million doses given to children aged three years and older in China, Chile, Brazil and elsewhere.
Recent data4 They report that in adults 60 and older, two doses of CoronaVac provide less protection against severe illness and death caused by Omicron than two doses of the mRNA-based vaccine made by Pfizer-BioN Tech, but three doses of either vaccine provide Very high levels of protection. This research has not yet been peer-reviewed.
analysis1 It was published online March 15 evaluating the effectiveness of CoronaVac in a population of 490,694 children aged three to five years in Chile, between early December and late February, when Omicron overtook Delta. Inactivated vaccines were 38% effective in protecting children from COVID-19 symptoms and 65% effective against hospitalization.
The results are a first for the effectiveness of COVID-19 vaccines in this age group. Children are at a very low risk of ending up in hospital when infected, which makes it difficult to notice the effect of vaccines, says study co-author Rafael Araus, a physician and epidemiologist at the University of Development in Santiago. Given this hurdle, Araus says, the vaccine’s performance is “very good.”
study2 From Argentina, published on April 19, they observed similar results with the Sinopharm vaccine in a group of 1.5 million children, which included a subgroup of 3-11-year-olds who received the vaccine. Two doses of the vaccine were 59% effective at preventing hospitalizations during the Omicron wave in 2022 — down from 83% from mid-December to mid-January, when both Delta and Omicron were in circulation.
Finally, study3 From Brazil, published on April 29, data on nearly 200,000 SARS-CoV-2 test results from children aged 6-11 were evaluated. The authors estimated that two doses of CoronaVac were 42% effective in protecting against COVID-19 in children, and 64% effective in protecting against hospitalization and mortality, between late January and mid-April.
Overall, the results show that vaccines cannot suppress viral circulation, but they are effective against severe disease, Cruz says. But Madi notes that the high number of unrecorded infections in children means that efficacy estimates may not compare vaccine-induced immunity with no immunity, but ‘hybrid’ immunity – conferred by both vaccination and infection – with immunity from infection alone.
Young children, small risks
Madi says he is concerned about the large number of children who need to be vaccinated “to prevent a single episode of hospitalization”. Unless vaccines can prevent infections and mild illnesses, which account for 99% or more of cases in children, “it would be a real stretch to justify this as a cost-effective strategy.”
“On an individual level — yes, vaccinating children is a good thing,” says Gagandeep Kang, a virologist at Christian Medical College in Vellore, India. But more studies are needed on how long the protection lasts and the breadth of vaccine coverage against emerging variants, she says.
Franco Marsico, a statistician at the Institute of Calculus at the University of Buenos Aires and co-author of the Argentina study, plans to track waning protection. “This is one of our main concerns as winter enters.”
Araus says the studies are another example of realistic evaluations of effectiveness that justify public health decisions after the fact. The big question, he says, for inactivated and other vaccine technologies is “whether or not to have a booster — and when.”