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Risk of SARS-CoV-2 reinfection in children compared to adults

Jacob Scott



The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak of coronavirus disease 2019 (COVID-19) led to the emergence of numerous studies meant to identify the immune correlates of this infection. Earlier, it has been found that infected and recovered adults were susceptible to reinfection, though rarely in the first phase of the outbreak.

Study: Risk of SARS-CoV-2 reinfections in children: prospective national surveillance, January 2020 to July 2021, England. Image Credit: Oleksandr Yakoniuk/Shutterstock

Recently, however, increasing rates of breakthrough infections and reinfections following vaccination and recovery from natural infection, respectively, point to waning immunity and immune escape due to the generation of new virus variants.

More data is required, especially in children largely neglected due to the low incidence of infection and symptomatic disease in this age group. A new study used national testing data over the first two years of the pandemic to estimate the reinfection risk in children relative to adults when exposed to both Alpha and Delta variants. This shows that reinfections were rare among children and mostly mild.


Earlier studies showed a strong immune response among children following exposure to SARS-CoV-2, both humoral and cell-mediated adaptive immune responses having been observed. The immune attack is directed mostly against the viral spike, but most cases are mild or asymptomatic, with the immunity persisting for 12 months or more.

This exceeds the period of active immunity in adults and seems to protect against newer variants of the virus. Adults have been vaccinated on a large scale in many countries, with early success in bringing down the incidence of new COVID-19 cases and hospitalizations. Still, waning immunity has seen a rise in breakthrough infections over time.

This has been aggravated by the rise of the new Delta variant that is much more infectious than earlier strains, which can evade natural and vaccine-induced immunity. The current study, available on the medRxiv* preprint server, aimed to explore the rate and risk of SARS-CoV-2 reinfections in children.

In England, SARS-CoV-2 testing was limited to symptomatic cases presenting at healthcare facilities. Presently, community testing is available freely, leading to about 100,000 tests being done each day in June 2020. This data was mined for the current study to understand reinfection risk in children over the first 19 months of the pandemic, while both Alpha and Delta variants were circulating.

What did the study show?

In England, during summer 2020, a low rate of infections then saw a rise just before the onset of Autumn, with the peak occurring in December 2020. This has been attributable to the emergence and rapid spread of the Alpha variant from November 2020 onwards. This was followed by a national lockdown, which saw cases declining rapidly.

During this period, few reinfections occurred in children, mirroring the low reinfection number at the community level. In March 2021, a six-fold rise in primary cases led to a small increase in reinfections as well, with a further sharp rise in May 2021.

In May 2021, infections rose again to a peak, as restrictions were relaxed simultaneously with the emergence and spread of the Delta variant. Therefore, reinfection rates followed the same trend as community infection rates with this variant. School closures led to a fall in primary infections and reinfections over the summer holidays.

The researchers found that the reinfection risk was in proportion to the risk of exposure to the virus. Most reinfections occurred during the time of maximum community transmission, at the time when the Delta virus was rampant.

Reinfections with the Alpha variant occurred mostly in those over 80 years of age, but the age distribution changed with increasing adult vaccination rates. By the time the Delta variant was circulating, younger adults less than 40 years of age were the major target of reinfection, these being largely unvaccinated or vaccinated with one dose.

In adolescents, July 2021 saw peak reinfection rates with the Delta wave, at 5.5 per 100,000, compared to <2 and <1 among children aged 5-11 years and <5 years, respectively. This followed similar trends among people aged 50-59 years who had received two doses of the COVID-19 vaccine in three of four cases. At least 93% had received one dose of the vaccine at this point.

The children were less prone to reinfection than adults, but the risk went up with age. The risk of adverse outcomes among children, including hospitalizations and intensive care admissions, was low with reinfections. In children, no deaths were reported to occur within 28 days of reinfection.

Throughout the study, primary infection rates were highest in infants but lowest among those aged 1-2 years. The pattern was reversed with reinfections, as described above.

The overall rate of reinfection was almost 70/100,000, but in adults, it was ~75 vs. ~21 per 100,000 in children. The rates were ~700 overall for reinfections, at 730 and ~340 per 100,000 in adults and children, respectively. Less than 5% of reinfected children needed hospital admission, and almost three-quarters of these had underlying medical conditions recorded at admission.

More reinfections among children were asymptomatic, at half, compared to infections, at 37%. Only four children had required ICU admission, and all were admitted during both primary infection and reinfection, with severe medical conditions. Thus, the exact contribution of SARS-CoV-2 to the severe phenotype is not clear.

There were 53 deaths within two months of the first positive COVID-19 test where this infection was recorded as the cause of death, all following primary infection.

What are the implications?

The study underlines the uncommon and mild phenotype of SARS-CoV-2 reinfections in children in England, reflecting the rates of community transmission. Most of them were related to the spread of the Delta variant in summer 2021. Despite the obvious limitations of using testing data, such as the reduced chances of testing among children due to the asymptomatic or very mild phenotype of primary infection or reinfection, the study also included the twice-weekly rapid home testing data from secondary schools, which could have led to lower rates of spread and higher rates of reporting among older children (11-16 years).

Exposure risks varied with the variant and the activity profiles, adults showing a different pattern from children. Testing probabilities also fluctuated over the study period. Nonetheless, the study successfully estimated the risk of reinfection over 19 months and compared it with that in adults. The high rates of infection among infants below the age of 1 year are probably due to newborns being tested after birth and testing being carried out at the time of presentation with fever or signs of infection.

A history of prior SARS-CoV-2 infection with one dose of the vaccine seems to confer broad and lasting immunity to reinfection. Even more importantly, to severe disease and death due to the infection, among children just as among adults. Further research will help uncover the risk of long COVID-19 in this age group.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:

Mensah, A. et al. (2021) “Risk of SARS-CoV-2 reinfections in children: prospective national surveillance, January 2020 to July 2021, England”. medRxiv. doi:

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Genetic bottlenecks could impact Wyoming toads’ ability to respond to new pathogens

Jacob Scott



A new study from North Carolina State University examines immune system diversity in the critically endangered Wyoming toad and finds that genetic bottlenecks could impact a species’ ability to respond to new pathogens. The findings could inform captive breeding strategies for endangered animal populations.

The Wyoming toad, Anaxyrus baxteri, suffered a severe population decline throughout the latter part of the 20th century due to factors including habitat destruction and fungal infection. The toad was brought into a captive breeding program in the 1990s in order to save the species. Scientists estimate a current wild population of only 400 to 1,500 animals, meaning that the toad is considered critically endangered.

Population reduction in this species created a genetic bottleneck to begin with, meaning the level of genetic diversity is already very small. This is the first study to look specifically at genetic diversity in the immune systems of these toads and how it could impact them as a population.”

Jeff Yoder, professor of comparative immunology at NC State and co-corresponding author of paper

Yoder, with co-corresponding author Alex Dornburg of the University of North Carolina at Charlotte, performed RNA sequencing on immune tissues from three healthy, retired Wyoming toad breeders. Study co-author Michael Stoskopf, who was on the Wyoming Toad Recovery Implementation Team established in 2008, obtained the samples.

“We were focused specifically on sequences encoding toll-like receptors – TLRs – and the proteins of the major histocompatibility complex, or MHC, expressed in these tissues,” says Kara Carlson, first author of the study and current Ph.D. candidate at NC State. “These sets of genes are major components of the immune system.”

TLRs are the first responders of the immune system, and are similar, or well-conserved, between species. The MHC, on the other hand, is a large and diverse group of genes that varies between species and individuals. It can determine why one group is more resistant to a particular pathogen than another.

“MHC genes are some of the most rapidly evolving sequences in the genome,” Carlson says. “So in a healthy population there’s a lot of variety that gets passed along to descendants, enabling the species at large to adapt to different pathogens. However, if disease survivors do so because of their MHC, then that group would have a similar MHC.

“The Wyoming toads that were brought into captivity to save the species were all able to resist the fungus that had decimated the population, but that could mean that their immune diversity is reduced.”

The researchers compared the TLR and MHC of the three Wyoming toads to each other, as well as to samples from a common toad and a cane toad. Both the common toad and the cane toad showed more MHC diversity than the Wyoming toad, even though the cane toad underwent a similar genetic bottleneck.

“The small sample size in this study – which was unavoidable due to the endangered status of the toad – nevertheless lays an important framework for conservation,” Carlson says.

“Amphibians in general don’t have as many genomic resources as other organisms,” Yoder says. “And captive breeding from a small population further decreases genetic diversity. But while these toads may be better protected against the fungal infection that nearly wiped them out, they may not be equipped to deal with new pathogens down the road.”

“While we weren’t necessarily surprised by the lack of immunogenic diversity in the Wyoming toad, it does spark an important question,” Dornburg says. “How equipped are other species of conservation concern for a battle with an emergent pathogen?”

“By understanding the genetic diversity of the immune system we can inform captive breeding to increase the chance of a species to resist disease in the wild,” Yoder adds. “Studies like this one are invaluable for captive breeding practices going forward.”

Journal reference:

Carlson, K.B., et al. (2022) Transcriptome annotation reveals minimal immunogenetic diversity among Wyoming toads, Anaxyrus baxteri. Conservation Genetics.

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Video conferencing hinders creativity

Jacob Scott



In-person teamwork has now transformed into virtual collaboration due to the COVID-19 pandemic. But does this affect innovation and creativity?

An interesting study on virtual communication led by Dr. Melanie S. Brucks from Columbia University and Prof. Jonathan Levav from Stanford University is published in the journal Nature. The study examines whether videoconferencing affects creative idea generation.

Study: Virtual communication curbs creative idea generation. Image Credit: Andrey_Popov / Shutterstock

Communication and collaboration

Collaboration is essential for several workplace tasks. It leads to innovation and idea generation. Historically, these collaborations have been in-person and required sharing of the same physical space. The use of traditional communication technologies like letters, emails, and phone calls hinder the smooth exchange of information and limits collaboration.

Now, due to advances in audio-visual technology, face-to-face interaction is possible via videoconferencing, allowing virtual collaboration. Videoconferencing has replaced in-person interactions due to pandemic-driven social distancing. Video interaction and in-person interaction allow communication of the same information.

While videoconferencing replacing in-person interaction has been beneficial in the social scenario, does it come with a cost in the workplace scenario? For example, does it affect collaborative idea generation?


The investigators performed a Laboratory experiment and a field experiment to test the difference between in-person interaction and videoconferencing in collaborative idea generation. First, they recruited participants and divided them into pairs: half of the pairs were assigned to an in-person setting, and the rest were assigned to a virtual setting.

Laboratory experiment

A total of 602 participants were recruited for the laboratory experiment and divided into pairs. The participants were in separate rooms in the virtual setting and communicated through videoconferencing. The pairs were allotted five minutes to generate creative uses for a frisbee (150 pairs) or bubble wrap (151 pairs) and then one minute to select their most innovative idea.

The pairs were evaluated by counting the number of creative ideas and ideas they generated. The virtual pairs generated significantly fewer total and creative ideas compared to in-person pairs.

So, virtual collaboration hampered creative ideas. This could be because the virtual space narrows the visual scope, which in turn narrows the cognitive scope. To assess the visual focus, two methods were used. Firstly, the participants had to recollect the individual props in the room and point them on a worksheet. Secondly, the participants’ eye gaze was recorded during the experiment.

The virtual pairs narrowed their focus to the screen. Compared to in-person pairs, they spent significantly more time looking directly at their partner and less time looking at the surrounding room, and remembered significantly fewer props in the surrounding room.

As a consequence, the virtual medium narrowed the visual focus and inhibited the generation of ideas.

However, these results are in the context of a controlled laboratory setting.

Field experiment

The experiment was repeated in ‘the field’ under actual work conditions within a large multinational telecommunications company to see if these results could be extrapolated to the real world. The field experiment was conducted in five country sites – in Europe, the Middle East, and South Asia. In this setting, the participants knew their partners and used video conferencing regularly for work. Moreover, it included domain experts highly invested in the outcome of the collaboration.

A total of 1,490 engineers were recruited to participate in an ideation workshop and randomly divided into pairs. The pairs were allotted an hour to generate product ideas and submit one idea as future product innovation for the company.

The engineer pairs who worked on the task virtually generated fewer total ideas and creative ideas than in-person pairs at all five sites.

However, the decision quality was not affected by virtual collaboration. The in-person pairs generated a significantly higher top-scoring idea, but the selected idea did not significantly differ in quality between the virtual pairs and in-person pairs.

Other reasons for reduced creativity

The could be other reasons why virtual collaboration negatively affected idea generation. Therefore, the investigators explored the alternative explanations.

More ideas

Since the in-person collaborators generated more total and creative ideas than the virtual collaborators, they could generate additional ideas similar to each other. However, upon semantic analysis, it was observed that they generated diverse and disconnected ideas.

Feelings of connection and trust

Studies have shown that feelings of connection and trust can foster team creativity. The virtual pairs may have reduced feelings of connection and trust toward their partner.

However, when assessed for subjective feelings of closeness, verbal and non-verbal behaviors, and mimicry, the virtual pairs were similar to in-person pairs in the laboratory experiment.

Thus, virtual and in-person interactions are very similar in terms of social connection or social behavior.

Communication coordination

Usually, there is a lack of coordination in a conversation in virtual interactions due to the absence of eye contact. However, it could not wholly explain the effect of virtual interaction on idea generation.

Interpersonal processes

This study also assessed the effect of interpersonal processes on idea generation. Interpersonal processes fear of evaluation, dominance, social facilitation, social loafing, social sensitivity, perceptions of performance, and production blocking were affected in virtual collaborations and these, in turn, affected idea generation.

Implications of the study

This study supports previous research suggesting that pairs perform better than large groups, both in-person and online. Therefore, this study recommends ideation in pairs and in person. Also, this study suggests that larger videoconferencing screens would not impact idea generation.

In-person collaborations offer a cognitive advantage. Now several workplaces are moving towards a hybrid setup. This study indicates that the creative idea generation should be reserved for in-person meetings.

Journal reference:
Brucks, M.S., Levav, J. (2022) Virtual communication curbs creative idea generation. Nature.,

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Gum Health Day 2022 calls for prevention, early detection, and effective treatment of gum diseases

Jacob Scott



“Treat your gums” is the slogan for Gum Health Day 2022, a worldwide awareness campaign organized by the European Federation of Periodontology (EFP). The event aims to inform the public of the detrimental effects of gum diseases – gingivitis, periodontitis, peri-implant mucositis, and peri-implantitis – on both oral and overall health. The campaign calls for the prevention, early detection, and – where necessary – effective treatment of gum diseases.

Although still poorly acknowledged by the public, gum diseases are chronic inflammatory conditions affecting a high proportion of adults worldwide, causing tooth loss and other problems in the mouth. Crucially, gum diseases are also linked to major systemic health issues including diabetes mellitus, cardiovascular diseases, chronic kidney disease, adverse pregnancy outcomes, rheumatoid arthritis, Alzheimer’s disease, erectile dysfunction, certain forms of cancer, and more severe Covid-19 outcomes. This means that gum diseases and their prevention and treatment are of major importance not only for oral health, but also for the whole body.

This year’s campaign focuses heavily on the treatment part – we know that millions of people suffer from gum diseases that can be treated effectively. ‘Treat your gums’ calls for this treatment – with all the documented positive effects for the mouth and whole body – to actually happen.”

Moritz Kebschull, coordinator of Gum Health Day 2022

That is why the hashtag for the campaign is #TreatYourGums, and why the recent EFP-produced clinical practice guidelines on the treatment of periodontitis are a major part of the Gum Health Day 2022 initiative.

“The new EFP-produced clinical practice guidelines on the treatment of all four stages of periodontitis are a crucial development, as they are the first high-quality international guidelines to outline a structured and easily implemented pathway for the efficient and effective treatment of gum disease,” Prof. Kebschull says. “In a nutshell, gum disease treatment that works!”

He adds: “It is important to underline that gum disease is one of the most widespread chronic diseases in the worldwide adult population, and that it is usually painless, so its early detection and successful treatment depends heavily on how fast the patient takes action.”

A major innovation of Gum Health Day 2022 is an EFP-designed “customized content generator”, a feature that allows the federation’s 37 affiliated national societies of periodontology, their individual members – as well as practices, hospitals, and members of the public – to customise their own Gum Health Day 2022 materials, based on a series of graphic templates and catchphrases.

In the framework of Gum Health Day 2022, the EFP encourages periodontists, dentists, researchers, and other health-related professionals to sign and disseminate the EFP Manifesto: Perio and General Health, an international call to action for the prevention, early detection, and treatment of gum disease. Individuals and organisations are invited to endorse it and join the 1,200+ professionals, dental practices, companies, and universities that have so far supported it.

The European Federation of Periodontology (EFP, is a non-profit organization dedicated to promoting awareness of periodontal science and the importance of gum health. Its guiding vision is “periodontal health for a better life.”

Founded in 1991, the EFP is a federation of 37 national periodontal societies that represents more than 16,000 periodontists, dentists, researchers, and oral-health professionals from Europe and around the world. It supports evidence-based science in periodontal and oral health, and it promotes events and campaigns aimed at both professionals and the public.

The EFP organizes EuroPerio, the world’s leading congress in periodontology and implant dentistry, as well as other important professional and expert events such as Perio Master Clinic and Perio Workshop. The annual Gum Health Day on May 12, organized by the EFP and its member societies, brings key messages on gum health to millions of people across the world.

The EFP also organizes workshops and outreach campaigns with its partners: projects to date have covered the relationship between periodontal disease and diabetes, cardiovascular disease, and caries, as well as women’s oral health during pregnancy.

The EFP’s Journal of Clinical Periodontology is the most authoritative scientific publication in this field. The federation also publishes JCP Digest, a monthly digest of research, and the Perio Insight magazine, which features experts’ views and debates.

The EFP’s work in education is also highly significant, notably its accreditation programme for postgraduate education in periodontology and implant dentistry.

The EFP has no professional or commercial agenda.

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