Coronavirus Research Tracking - 1 July
Vaccine effectiveness in kids, viral shedding, BA.5 characteristics, long Covid, aerosols, masks
This week, a review of the humoral responses to infection and vaccination, effectiveness of the Pfizer vaccine in children, the length of time people shed the virus after an Omicron infection, and Omicron outcompetes Delta in vaccinated but not unvaccinated hamsters.
In other papers, the improving understanding about the BA.5 variants, the relatively short life of the virus in aerosols, long Covid prevalence, pan-variant neutralising antibodies, and masks with anti-viral coatings.
The Research Tracker is prepared by Dr Robert Hickson for the Science Media Centre.
Vaccine-related papers
What we know about antibody responses to SARS-CoV-2
A review published in Nature Immunology discusses what has been learnt about the humoral immune response to SARS-CoV-2. The most potent antibodies tend to be effective against only one or a few variants.So a vaccine able to be effective against a range of variants will need to balance generating antibodies with high potency against antibodies that are able to bind to many variants.
Effectiveness of Pfizer/BioNTech vaccine in children
An Israeli study found that two Pfizer/BioNTech doses provided moderate protection against Omicron infection for children aged 5-to11, at least over the short term. Vaccine effectiveness against symptomatic infection was around 48% between one and three weeks after the second dose.
Five to six year olds may receive slightly greater protection from the vaccine than 10-to-11 year old children, although the confidence interval for effectiveness was very broad for young children. Children receive a lower dose of the vaccine than adults. The paper was published in the New England Journal of Medicine.
People with Omicron infections can shed viable virus for more than 5 days
People infected with the Delta or Omicron BA.1 variants can shed virus for more than five days after symptom onset or a PCR positive test. For Omicron the infectious period was 3-to-9 days. Similar times were seen for PCR tests to become negative. Vaccination did not significantly affect the period of viral shedding. The authors suggest a five day quarantine period may be too short to reduce transmission risks.
The study used the ability to infect cultured cells as a proxy for infectiousness, but this needs to be investigated further. Only 66 infected people were involved in the study, so further research is necessary. Viral shedding in other Omicron variants was not studied. The paper was published in the New England Journal of Medicine.
Omicron outcompetes the Delta variant in vaccinated but not unvaccinated hamsters
The advantages of immune evasion were shown in experiments of unvaccinated and vaccinated Syrian hamsters. The Delta variant was able to outcompete the Omicron variant in unvaccinated animals. Both variants were equally transmissible.
However, about three months after vaccination, Omicron outcompeted Delta. This was attributed to waning immunity and the antibodies being less effective against Omicron. Similar results were found using cell cultures and sera from vaccinated animals.
Small numbers of hamsters were involved in the study. The authors emphasise that the results do not mean that unvaccinated people should not get vaccinated, nor that people should not get booster doses of vaccines. There is good evidence for vaccines reducing the risk of developing severe Covid-19 after an Omicron infection. The paper was published in Science.
Non-vaccine-related papers
BA.5 variant
The UK Health Security Agency has released another technical briefing on variants of concern in England. The BA.5 variant has a transmission advantage over BA.4. Hospitalisation risk has slightly increased in recent months, but it is unclear what is causing this.
A news article in Nature also discusses the BA.4 and BA.5 variants. It notes that the proportion of a population infected with BA.5 may vary between countries due to different vaccination rates and previous infection waves affecting their immunity profiles.
The BA.4/BA.5 wave in South Africa did not result in a significant rise in severity of cases (paper not yet peer reviewed). The Nature article notes, though, that this may not be the same in countries with more older people.
Eric Topol provides an excellent overview of the BA.5 variant in his Ground Truths newsletter. It covers the variant’s characteristics, prevalence, and potential protective measures that can be used against it.
Potential for resistance to Paxlovid to develop
Mutations seen in SARS-CoV-2’s main protease could provide resistance against Paxlovid. Analysis of genomes found 66 common mutations in the gene. The majority reduced the enzyme’s function, but 11 would reduce binding of nirmatrelvir, the active compound in Paxlovid, without affecting the protease’s activity.
The authors recommend that all these mutation sites be closely monitored to see if their prevalence increases. The paper has not yet been peer reviewed.
Short lived infectivity in aerosols
Infectivity of SARS-CoV-2 in aerosols drops significantly after five minutes. Previous research indicated the half-life of the virus in aerosols may be more than one hour. Levels of relative humidity below 50% result in much more rapid loss of infectivity than higher humidity levels. This is due to crystallisation of salts in the droplets when humidity is lower.
High levels of CO2, usually seen in crowded poorly ventilated rooms, may prolong the viability of the virus through decreasing the pH in aerosols. The effect of pH on viral viability was assessed in tissue cultures, rather than in aerosols in a room. The paper was published in Proceedings of the National Academy of Sciences.
Long Covid prevalence in the UK
The proportion of Covid-19 cases in the UK that have symptoms persisting for at least three months may lie between 8 and 17%. The conclusions are based on analysis of 10 longitudinal studies of long Covid in the UK. The variation in results is attributed to different definitions of symptoms between studies, as well as other methodological differences.
When looking at 1 million health records, the proportion of people reporting long lasting symptoms was much lower than in the longitudinal studies, indicating relatively few people with long Covid may seek medical care.
Older age, female sex, white ethnicity, poor pre-pandemic physical and mental health, being overweight or obese, and having asthma were associated with prolonged symptoms. The paper was published in Nature Communications.
An article published in The Conversation estimated that in Australia about 5% of people infected develop long Covid. This article wasn’t peer reviewed.
Long Covid in hamsters
SARS-CoV-2 is more likely to cause long-lasting symptoms than Influenza A virus in Syrian hamsters. Covid caused permanent injuries to the lungs and kidneys, and also affected the olfactory bulb.
Inflammatory responses in the olfactory bulb resulted in hamsters with Covid taking longer to find buried food and reduced burying activity for a month after the infection cleared.
Small numbers of hamsters were used for each experiment. The paper was published in Science Translational Medicine.
Neurodegenerative risks after Covid similar to other respiratory infections
A large Danish study found that the relative risk of neurodegenerative and cerebrovascular disorders increases after a Covid-19 infection, but the risk was usually similar to that after other respiratory infections. Outcomes from Covid infections were compared to those following influenza or bacterial pneumonia.
Only the relative risk of ischemic stroke was greater in hospitalised Covid cases , compared with hospitalised influenza cases and people over 80 with bacterial pneumonia. Infection-induced inflammation in the brain is considered to be a cause of the increased risks following respiratory infections. The paper was published in Frontiers in Neurology.
Antibodies that can neutralise most variants
The monoclonal antibody bebtelovimab is able to neutralise all current Omicron sub-variants. This antibody recognises a conserved region in the spike protein. Only a small number of participants were included in testing. The paper was published in The Lancet Infectious Diseases.
Another study found that a monoclonal antibody generated in a mouse is also able to neutralise all current variants of concern. It partly overlaps the bebtelovimab binding site. The paper has not yet been peer reviewed.
Masks with an antiviral coating
Incorporating materials with antiviral properties into N95 masks improves mask effectiveness and longevity. Masks incorporating ammonium polymers were able to disrupt viruses with lipid envelopes, as well as Staphylococcus aureus and Escherichia coli bacteria. The polymer can be added after the mask is made.
The polymer reduced viral viability between 1.7 and 4.3 log values, depending on the virus and assay method. Mask breathability was not significantly affected. SARS-CoV-2 was not one of the viruses tested, although other human coronaviruses were. The paper was published in ACS Applied Materials Interface.