Vaccinated children less likely to experience lingering COVID-19 symptoms

SARS-CoV-2 vaccination appears to confer protection against long COVID in the paediatric population, with the protective benefit being stronger in teens.

In a large study involving 1,037,936 children, the adjusted vaccine effectiveness within 12 months was 35.4 percent (95 percent confidence interval [CI], 24.5–44.5) against probable long COVID (ie, a single diagnosis code specific for long COVID) and 41.7 percent (95 percent CI, 15.0–60.0) against diagnosed long COVID (at least two diagnosis codes). [Pediatrics 2024;doi:10.1542/peds.2023-064446]

Of note, vaccine effectiveness was higher for adolescents (12–17 years: 50.3 percent, 95 percent CI, 36.3–61.0) than for younger children (5–11 years: 23.8 percent, 95 percent CI, 4.9–39.0).

Mediation analysis showed that the effectiveness of vaccine against long COVID was closely linked to its effectiveness against the antecedent COVID-19 episode.

“Our finding of a protective effect against long COVID in children are consistent with those observed in adults, while the vaccine effectiveness estimates in our study are lower than studies assessing the short-term effect of vaccines in 1 week to 1 month after vaccination,” the investigators noted. [EClinicalMedicine 2022;53:101624]

“[Meanwhile, the] higher vaccine effectiveness for adolescents is similar to studies examining acute [COVID-19] infection,” they added. [MMWR Morb Mortal Wkly Rep 2022;71:422-428]

Waning protection

The protective effect of vaccination waned over time, with vaccine effectiveness dropping from 61.4 percent (95 percent CI, 51.0–69.6) at 6 months to 10.6 percent (95 percent CI, –26.8 to 37.0) at 18 months.

Vaccines, according to the investigators, become less effective at preventing long COVID, just as they also become less effective at preventing SARS-CoV-2 infection after a while. This is expected, they added. [PLoS Pathog 2021;17:e1009509; Pediatrics 2023;doi:10.1542/peds.2022-060894; N Engl J Med 2022;386:1899-1909; N Engl J Med 2022;387:525-532]

“The reasons include reduced neutralization efficiency against newer strains and waning of pre-existing antibodies over time. It is also possible that long COVID starting several months after acute infection, or delayed diagnosis or recognition of long COVID, may contribute to this phenomenon,” the investigators explained. [Nat Rev Immunol 2022;22:57-65]

“Further, waning effect may reflect the impact of successive infections rather than late-onset long COVID. This is difficult to assess analytically, given fewer COVID-19 episodes are being documented in the electronic health records during the Omicron era,” they continued.

As such, the investigators underscored a need for continued evaluations of vaccine effectiveness to address whether these waning effects can be overcome through booster or annual vaccine doses.

Large cohort of children

A total of 480,498 children were in the 5–11-year-old group, and 719,519 were in the 12–17-year-old group. More than half of the population (55 percent) had received at least one SARS-CoV-2 vaccine, and 84 percent of vaccinated children received two or more doses. Vaccinated children were older, had lower baseline healthcare use, and had fewer chronic conditions.

Probable long COVID was documented in 4.5 percent of the population, while diagnosed long COVID was reported in 0.7 percent. Long COVID was less likely among boys and children with non-Hispanic Black or Asian ethnicity.

Despite the presence of several limitations such as the use of electronic health data from 41 health systems across the US, “our results provide substantial evidence in a large and diverse cohort of children,” the investigators said.

“This study adds to the growing body of knowledge about [the] mitigating effect of vaccines on COVID-19, while demonstrating the need for further research [using] a range of designs to examine the protective effect of these vaccines against subsequent strains and to help guide vaccine policy,” they added.