A health worker gives the CoronaVac COVID-19 vaccine to a child in Santiago. Credit: Marcelo Hernandez / Getty
Three new studies offer a first look at how well some of the most widely used COVID-19 vaccines protect young children from coronavirus1-3. The results – including data from young children as young as three – sparked mixed responses among researchers as to whether vaccines should be recommended for use in children.
The study examines two “inactivated” vaccines that rely on whole killed viruses developed by Chinese scientists. Results from Argentina, Brazil, and Chile show that in children, vaccines provide poor protection against SARS-CoV-2 infection and moderate protection against symptomatic COVID-19. Studies also show that vaccines are less effective against the now dominant version of Omicron than the earlier version of Delta. The studies have not yet been reviewed by partners.
The findings lead some scientists to say that both vaccines should be used to protect children, especially because the technology of inactivated viruses has a long history of safety in conventional vaccines given to babies against polio and influenza. “It is important to vaccinate children to avoid serious cases,” said Annie Cruz, an epidemiologist at the London School of Hygiene and Tropical Medicine who co-authored the study.
However, others note that severe illness and death from COVID-19 are rare in children, and vaccines do not offer impressive protection against SARS-CoV-2 infection or mild illness. Many children, including in well-off environments such as the United States, have been infected with the virus at least once and may have already acquired some immunity, said Shabir Madhi, a vaccinologist at the University of the Witwatersrand in South Africa. The data on vaccines, he says, do not “support the thesis of universal vaccination of young children.”
Modest protection
New research presents data on two vaccines that are among the world’s most widely used vaccines against COVID-19 in adults – CoronaVac, manufactured by Beijing-based Sinovac, and a vaccine produced in Beijing by the state-owned Sinopharm. More than 5 billion doses of vaccine have been given worldwide, according to health analytics firm Airfinity in London and non-profit organization Our World in Data in Oxford, UK. This total includes many millions of doses given to children aged three and over in China, Chile, Brazil and elsewhere.
Recent data4 suggest that in adults 60 years of age and older, two doses of CoronaVac offer less protection against severe illness and death caused by Omicron than two doses of the messenger RNA vaccine produced by Pfizer-BioNTech, but three doses of each of the two vaccines provides very high levels of protection. This study has not yet been tested by partners.
An analysis1 published online on March 15 evaluated the effectiveness of CoronaVac in a population of 490,694 children aged three to five in Chile, between early December and late February, when Omicron overtook Delta. Inactivated vaccines are 38% effective in protecting children against symptomatic COVID-19 and 65% in hospitalization.
The results are the first for the effectiveness of COVID-19 vaccines in this age group. The study’s co-author, Rafael Araos, a doctor and epidemiologist at the University of Development in Santiago, said children were at very low risk of being hospitalized when they became infected, making it difficult to monitor the effects of vaccines. Given this hurdle, the vaccine’s effectiveness is “pretty good,” says Araos.
A study2 from Argentina, published on 19 April, saw similar results with the Sinopharm vaccine in a cohort of 1.5 million children, which includes a subgroup aged 3-11 who received the vaccine. Two doses of the vaccine were 59% effective in preventing hospitalization during the Omicron wave in 2022 – a drop of 83% between mid-December and mid-January, when both Delta and Omicron were circulating.
Finally, a study3 from Brazil, published on 29 April, estimated data on nearly 200,000 SARS-CoV-2 test results in children aged 6-11 years. The authors estimate that two doses of CoronaVac were 42% effective in protecting against COVID-19 in children and 64% effective in protecting against hospitalization and death between late January and mid-April.
Overall, the results show that vaccines cannot suppress viral circulation, but are effective against serious diseases, Cruz said. But Madhi points out that the high number of unrecorded infections in children means that efficacy evaluations probably do not compare vaccine-induced immunity with lack of immunity, and “hybrid” immunity – provided by both vaccination and infection – with immunity only from infection.
Young children, little risk
Madhi 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 infection and minor illnesses, which account for 99% or more of cases in children, “it would be very difficult to justify this as a cost-effective strategy.”
“On an individual level, yes, vaccinating children is a good thing,” said Gagandip Kang, a virologist at Christian Medical College in Weller, India. But more research is needed on how long the protection and coverage of vaccines against emerging variants lasts, she said.
Franco Marsico, a statistician at the Institute of Calculus at the University of Buenos Aires and co-author of the study in Argentina, plans to track declining defenses. “This is one of our main concerns when we enter winter.”
Araos says the studies are another example of real performance assessments that justify public health decisions after the fact. The big question, he says, about inactivated and other vaccine technologies is “whether to step up or not – and when.”
Add Comment