17 August 2021 Episode 163 : Update on COVID in children : contribution to epidemic and prevention

Tue, 08/17/2021 - 17:05

Dear colleagues,

We are all concerned about the effect of school re-opening on the epidemic, especially since primary school children have not been vaccinated.  In this episode, I will discuss recent evidence on this age group, mainly from the US: what is the role of these children in the epidemic and what can we do to mitigate the impact of school reopening, in order to avoid a further surge in the general epidemic and prevent new school closures?

For the papers see:    

Some recent US lay press papers

163-1: 16 Aug record number of children COVID hospitalized:

  • 1900 children in hospital mainly in Southern states, after reopening of schools: “worse” than in 2020 !?
  • Several Republican governors (Florida, Mississippi, Texas) are against mandatory mask wearing by children;
  • Some counties resist their governor and are supported by central government.
  • National Education Association, America’s largest teachers’ union, has come out in support of mandatory vaccination for its members

163-2: 17 Aug specifies that the hospitalization rate for children in whole US is now 261 per day, which is 20 % more than in the winter.  Mainly due to 3 states: Florida, Georgia and Texas.

California is doing relatively well with 18 children hospitalized per day, 10 times more than 2 months ago, but still 3 times less than winter peak.  Reasons:

  • Higher overall vaccination
  • Mask wearing
  • Regular testing of unvaccinated workers

Mortality in children remains low: 30 children out of 64,000 COVID deaths in California

Doctors observe that previously mainly children with pre-existing co-morbidities were hospitalized, but now more previously healthy children get seriously ill.

Ep 163-3: 12 Aug: USA Today

  • Make sure everybody around children less than 12 is vaccinated
  • Delta variant certainly more contagious but unclear if more pathogenic
  • Already 25 cases of dual RSV and COVID infection at Texas Children's Hospital

Ep 163-4: According to Medical Trends, we can expect approval of mRNA vaccines for children under 12 only by the end of 2021.  Pfizer might release the first results in September.



Ep 163-5 : A short reminder of how COVID presents in children:

  • Asymptomatic in 50 % (or more?)
  • Symptoms:
    • fever, cough, rhinorrhea, sore throat
    • headache, vomiting, diarrhea, fatigue,
    • tachycardia, tachypnea, myalgia, rash
    • ageusia/anosmia not frequent but strong predictor of SARS-CoV-2
  • Severe and critical cases (including Multi Inflammatory Sundrome-Children):
    • Decrease with increasing age: 10 % in < 1 yrs to 3 % in > 15 yrs
    • More if “co-morbidities”: chronic respiratory illness including moderate-to-severe asthma, obesity, diabetes, sickle cell disease or cancer and infants (age < 1 year)
    • May develop neuro logic manifestations, and occasionally acute disseminated encephalomyelitis, acute transverse myelitis, respiratory failure;  myocarditis ; shock; ocular symptoms) acute renal failure, and multi-organ system failure
  • Overall Case Fatality Rate is < 1 %


Epidemiology and transmission

Ep 163-6: Situation in US:

  • Clearly rising trend for both children and adults (slide 10)
  • Total 5,864 per 100,000 children or 14 % of total cases (slide 11)

Ep 163-7: Adjustment for number of tests in Ontario shows that reported infection rates are underestimated in 10-29 years old men (and to a lesser extent women!.  See Fig


Ep 163-8: A study on 6280 households with index also in Ontario shows

  • High transmission rate (27%)
  • Younger children (0-13 yrs) are more likely to transmit with older children (14-17 yrs),
  • highest odds of transmission for children aged 0 to 3 years


Ep 163-9: A much smaller study on 87 households in Finland shows:

  • Overall transmission rate was 48 %.
  • Highest transmission was if the primary case was 10-19 yrs.
  • Participants who required hospital care had initially 5-fold IgG Ab concentrations compared to cases with mild symptoms and 8-fold compared to asymptomatic cases.


Ep 163-10: COVID-19 Projections for primary school children in Fall 2021 (USA):

  • Without interventions the vast majority of susceptible students will become infected.
  • Universal masking can reduce student infections by 26-78%,
  • And biweekly testing along with masking reduces infections by another 50%.


To:         prevent new infections in the community,

limit school absences,

and maintain in-person learning,


Interventions such as masking and testing must be implemented widely, especially among elementary school settings in which children are not yet eligible for the vaccine.



More on effects of Non-Pharmacological Interventions in children

  1. Avoid school closure

Ep 163-11: A literature review on the impact of school closures in the US

Prolonged closures had negative effects on children under 12: physical, mental, and social well-being

And reduced the number of health and social workers, hindering the reopening of the country

Conclusions:      School closures were over-weighted against the mitigation of COVID-19 transmission.

A safe reopening of all primary schools in the US should be of top priority.


  1. Ventilation versus air purifiers (AP)

Ep 163-12: A detailed technical study on the effect of different types of air purifiers in classrooms

Window ventilation reduces respiratory particle concentration and improves air quality in terms of humidity and CO2. However, as mentioned above, window ventilation is not a reliable measure to reduce the concentration of virus-laden particles to a defined degree.

Compared to conventional window ventilation, the use of well-designed APs achieves a significantly greater reduction in potentially virus-laden particles indoors and does so reliably. 

AP's has a particularly positive effect when people are in small rooms for long periods of time and maybe talking, singing, or shouting

  1. Masking

Ep 163-13:   When do elementary students need masks in school?


With the delta variant and no student vaccination,

assuming simple ventilation and handwashing reduce the secondary attack rate by 40%,

if decision-makers seek to keep the monthly probability of an in-school transmission below 50%, additional mitigation (e.g., masking) would need to be added at a community incidence of approximately 4/100,000/day. (Note: present incidence in Belgium = 16/100,000/day)


Ep 163-14: the American Academy of Pediatrics is very formal:

  • Universal mask wearing in schools from 2 years on
  • Also physical distancing, testing, contact tracing, ventilation, cleaning and disinfecting.
  • Vaccinate everyone eligible

Goal: maximal avoidance of school closure !


  1. Testing

Ep 163-15: POTENTIAL VALUE OF (weekly) SCREENING IN K-12 (primary) SCHOOLS

  • May reduce total numbers of infections among educators, staff, students, and household members by up to 90%,
  • Provides data to assess and guide in-school mitigation strategies.
  • Reassurance to parents and teachers that in-school learning is safe


Advantages and drawbacks of rapid tests and PCR are discussed (see Table)


Ep 163-16Saliva molecular testing bypassing RNA extraction is suitable for monitoring and diagnosing SARS-CoV-2 infection in children

In adults, accuracy of saliva RT-qPCR test was 98.0%  compared to Naso-Pharyngeal-RT-qPCR.

In children: sensitivity, specificity, and accuracy of saliva-based RT PCR was 84, 100 and 90 % irrespective whether RNA extraction was performed.



Ep 163-17: COVID-19 mRNA vaccination during lactation

  • Is safe for mother and child
  • IgG antibodies in milk, but not found in infant


Ep 163-18:  Vaccinated individuals, who get infected with Delta have similar viral loads and infectious virus in nasal swabs as unvaccinated subjects (Wisconsin USA).

Therefore: Vaccinated individuals should

  • continue to wear face coverings in indoor and congregate settings,
  • also being tested for SARS-CoV-2 if they are exposed or experience COVID-like symptoms.


Ep 163-19: Prevention of mutations by vaccination

Vaccination coverage rate is inversely correlated to the mutation frequency of the SARS-CoV-2 delta variant in 16 countries (R2=0.878),

→ full vaccination against COVID-19 is critical to suppress emergent mutations.



  1. Additional evidence that young children significantly contribute to household transmission
  2. Various modeling exercises and observations indicate the school re-opening will boost the epidemic, since primary school children are not vaccinated and get infected with highly contagious Delta variant.
  3. Application of universal masking from 2 years on, along with ventilation, hygiene, distancing (bubbles) and testing, tracing and quarantine.
  4. Potential role for (bi)weekly screening at an incidence lower than present incidence in Belgium. Saliva + PCR very sensitive.
  5. As soon as vaccination for children below 12 is approved, it can contribute to herd immunity and prevention of viral evolution.