Assessing the transition of COVID-19 burden towards the young population while vaccines are rolled out in China*

Abstract

SARS-CoV-2 infection causes most cases of severe illness and fatality in older age groups. Over 92% of the Chinese population aged ≥12 years has been fully vaccinated against COVID-19 (albeit with vaccines developed against historical lineages). At the end of October 2021, the vaccination programme has been extended to children aged 3–11 years. Here, we aim to assess whether, in this vaccination landscape, the importation of Delta variant infections could shift COVID-19 burden from adults to children. We developed an age-structured susceptible-infectious-removed model of SARS-CoV-2 transmission to simulate epidemics triggered by the importation of Delta variant infections and project the age-specific incidence of SARS-CoV-2 infections, cases, hospitalizations, intensive care unit admissions, and deaths. In the context of the vaccination programme targeting individuals aged ≥12 years, and in the absence of non-pharmaceutical interventions, the importation of Delta variant infections could have led to widespread transmission and substantial disease burden in mainland China, even with vaccination coverage as high as 89% across the eligible age groups. Extending the vaccination roll-out to include children aged 3–11 years (as it was the case since the end of October 2021) is estimated to dramatically decrease the burden of symptomatic infections and hospitalizations within this age group (39% and 68%, respectively, when considering a vaccination coverage of 87%), but would have a low impact on protecting infants. Our findings highlight the importance of including children among the target population and the need to strengthen vaccination efforts by increasing vaccine effectiveness.

Relationship of close contact settings with transmission and infection during the SARS-CoV-2 Omicron BA.2 epidemic in Shanghai

“…However, our results suggested that susceptibility to the SARS-CoV-2 Omicron variant was greater in children and adolescents than in adults aged 18–29 years. The results might be related to the vaccination strategy at that time, which did not include children and adolescents; there is additional evidence that this vaccination strategy might increase SARS-CoV-2 infections in children and young adolescents 34. Our analysis of transmission capacity found that cases aged 0–4 years and 60 or more years had higher transmission capacity than adults.…”

Predictive models for health outcomes due to SARS-CoV-2, including the effect of vaccination: a systematic review

“…Heterogeneous vaccine was indicated for high-income countries in two (0.5%) articles [ 106 , 382 ]. In 95 articles (23.1%), the difference in days between administered doses were considered; out of these, 22 articles (23.2%) considered a 21-day interval between doses [ 55 , 60 , 69 , 100 , 122 , 133 , 134 , 140 , 187 , 216 , 217 , 221 , 302 , 303 , 329 , 330 , 335 , 342 , 383 , 384 , 424 , 425 ], while 22 (23.2%) considered a period of 21- to 28-day interval [ 42 , 90 , 116 , 119 – 121 , 136 , 142 , 151 , 155 , 184 , 204 , 205 , 258 , 260 , 273 , 324 , 328 , 351 , 354 , 356 , 366 ]. Additionally, 11 (11.6%) articles considered a period equal to or greater than three months [ 203 , 211 , 222 , 269 , 300 , 314 , 317 , 333 , 334 , 350 , 361 ].…”

Age-specific transmission dynamics under suppression control measures during SARS-CoV-2 Omicron BA.2 epidemic

“…The age for the cases of Shanghai epidemic tended to be younger than those in the epidemic of Wuhan [ 27 , 28 ] and other localized outbreaks[ 38 ]. Cases infected with Omicron variant were found to be younger than cases infected with other variants [ 35 ], partly due to COVID-19 vaccination [ 13 ]. The overall SAR of the epidemic was estimated to be 24.17% (95% CI: 23.09% to 25.25%), which was consistent with previous studies [ 39 – 42 ].…”

“…Although the transmission rate and SAR in children and adolescents were lower, the transmissibility of them to other household members is not negligible. Extending vaccination to children aged 3–11 years would protect them from infection and reduce the transmission of this age group [ 13 ]. Cases with self-isolation at home could still infect susceptible people, such as their family members or neighbors [ 7 , 47 ].…”

“…Most studies suggested that the susceptibility of children was lower than that of adults and the elderly [ 7 – 10 ] or no significant difference in infectivity among different age groups [ 7 , 8 ], while other studies found an increased transmissibility in adults or elderly people [ 11 , 12 ]. The vaccination coverage varied with age, which might drive the transition of COVID-19 burden [ 13 ]. Assessing age-specific susceptibility and transmission risk is conductive to understand transmission dynamics and improve the effectiveness of interventions through prioritizing different interventions in different age groups.…”