Does vaccinating adults also stop children from spreading COVID?


Children in the city of São Paulo hold kits including disinfectant products and face masks for children.Credit: Andre Penner / AP / Shutterstock

Unvaccinated children appear to be reaping the rewards of mass COVID-19 vaccination programs in many parts of the world. Infections in children have decreased as adults get vaccinated. But experts disagree on whether this means unvaccinated children are unlikely to become a “reservoir” of infection – and a potential hotbed for the emergence of new variants.

The answer determines whether children in rich countries should be given priority for immunization – or whether their doses should go to poorer countries instead.

Compelling data on the impact of adult vaccination on children comes from the small town of Serrana in the Brazilian state of Ṣo Paulo, where 98% of adults have been vaccinated. The city was the site of a unique experiment Рdubbed Project S Рto measure the actual effectiveness of CoronaVac, developed by Beijing-based pharmaceutical company Sinovac.

Compared to other vaccines, Sinovac had less success in preventing symptomatic infections in some previous clinical trials, with efficacy rates as low as 50%.

But last week, researchers from the Butantan Institute in the city of São Paulo detailed at a press conference a striking reduction in COVID-19 cases and deaths: symptomatic cases fell by 80% and 95% death. Only 62% of Serrana’s 45,000 residents are adults, but a similar drop in symptomatic infections has occurred in unvaccinated children, according to Ricardo Palacios, the epidemiologist who led the study.

“That was one of our concerns – that if you vaccinate everyone else, the disease is likely to be concentrated in children and adolescents,” he says. “But we didn’t see him.”

Collective immunity?

Similar scenarios have occurred in countries with high vaccination rates, such as Israel and the United States. In the latter, cases in children (usually those under 18) decreased by 84% between January and May. Just over half of the American population – mostly adults – have received at least one dose of the vaccine.

“It makes sense,” says Monica Gandhi, an infectious disease physician at the University of California, San Francisco. Vaccinating adults protects others who are not vaccinated. “That’s really what collective immunity means,” she said.

Gandhi also points out that children are less likely than adults to transmit the virus – another reason why they might not act as effective reservoirs of infection.1. The way the virus affects children is “just different,” she says, possibly because children’s airways have fewer receptors than SARS-CoV-2 uses to get into cells.

In Israel, infection rates have dropped among those eligible for vaccination, from 559 cases per 100,000 people aged 16 and over in mid-January to just 1.5 per 100,000 today. Most schools reopened in March, but rates of unvaccinated children also plunged, from 546 per 100,000 to 1.5 per 100,000 among those 11 and under, for example.

This suggests that children are most often infected from adults, says Eric Haas, a doctor specializing in pediatric infectious diseases and epidemiologist at Israel’s Ministry of Health in Jerusalem. “Otherwise, you would expect that if the kids went back to school, they would just get infected en masse.”

Children wearing masks sit on the floor of their classroom at a school in Jerusalem, Israel.

Children return to school in Jerusalem after nationwide lockdown in Israel.Credit: Nir Alon / ZUMA Wire / Shutterstock

A mixed picture

But not everyone reads data this way. Julian Tang, a virologist at the University of Leicester, UK, says the rapid rollout of vaccination in Israel may have helped eliminate infections in all age groups. “By the time they finished vaccinating adults, there was no longer a source [of infection] adults to pass on to children, and then go to schools, ”he says.

And early data from the UK – where the vaccination rate is 60% – paints a more complicated picture when it comes to unvaccinated children and their potential for spreading COVID-19.

By the end of May, cases in high school children had fallen from a high of around 600 cases per 100,000 in January to less than 100 per 100,000. Among young schoolchildren, the numbers are now even higher. low.

But recent data also suggests that unvaccinated children could still be important vectors for the spread of the virus. In May, nearly 100 outbreaks – defined as two or more cases – occurred in primary and secondary schools in England.

This number is small, however, representing only a “tiny proportion” of England’s 25,000 schools, explains Shamez Ladhani, a pediatric infectious disease physician at Public Health England. It also notes that overall infection rates among school-aged children changed little in the six weeks after schools reopened.

Circulating variants

Nonetheless, Tang says transmission in schools should not be ignored. The vaccine’s rollout in Britain has been slower than that in Israel, he argues, and school reopens have coincided with the increased spread of B.1.617.2 – also known as the Delta variant – in British communities. As a result, the virus could continue to circulate in children.

This is an important point, he says, because the longer the pandemic continues, the greater the chance that new variants with some vaccine resistance will emerge.

The extent to which unvaccinated children act as propagators has implications for whether they should be vaccinated once the adult population has been vaccinated – an issue that is hotly debated.

In the United States, the Food and Drug Administration approved the Pfizer vaccine for children between the ages of 12 and 18 on May 10, and more than 7 million of those children have now received at least one dose. Agencies in Japan, the UK, the EU and elsewhere have since followed suit.

But severe COVID-19 in children is rare2. A May 2020 analysis in 26 countries estimated that only 0.14% of children infected with SARS-CoV-2 develop dangerous inflammation3. Other complications are also rare, Ghandi says.

Due to the lower risk, the World Health Organization maintains that immunizing children is not a high priority, given that global supplies are insufficient to immunize all adults.

“Extremely disturbing”

“You have countries that are basically vaccinating people who don’t really need it, while there are a lot of other countries that are in desperate need of the vaccine,” says Kim Mulholland, pediatrician and vaccine researcher at Murdoch Children’s. Research Institute in Melbourne, Australia. . “I find this extremely worrying. “

But Haas would like vaccination in Israel to be extended to children between the ages of 12 and 15. Although the risk of serious illness is lower for children, “it’s not ‘without risk’,” he says. Vaccinating adolescents would also prevent further disruption to schools and provide herd immunity to unvaccinated adults, he says.

Tang also considers vaccination of children to be crucial in controlling the pandemic. This would eliminate them as a potential reservoir for asymptomatic infections and prevent the emergence of new variants, he says.

In an ideal world, Tang adds, you would vaccinate all age groups, so that new variants do not appear in unvaccinated populations of adults or children. Until vaccine production meets demand, it is important to immunize not only adults in low-income countries, but also children in places that already have good immunization coverage. “You can do a bit of both,” he says.

About Mark A. Tomlin

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