Coronavirus Research Tracking - 29 July
New vaccines, reinfection risks, infectious period, infection risk in children, pandemic origin
This week, new types of vaccines in development, effectiveness of boosters, vaccine effectiveness in young children, and reduced reinfection risks after vaccination.
In non-vaccine research, auditing which RATs work against Omicron, how long people remain infectious, lower risk of infection in children, and support for a seafood market origin for the pandemic.
The Research Tracker is prepared by Dr Robert Hickson for the Science Media Centre.
Vaccine-related papers
Nasal vaccines require more support
More funding is need to expedite development of nasal vaccines, an opinion published in Science Immunology advocates. The authors suggest that greater investment & other support, as seen for Operation Warp Speed, is required to quickly develop and manufacture nasal vaccines for Covid-19. The article notes that at least 12 nasal vaccines are already in development, but progress will be slow without support for manufacturing, regulatory, and distribution steps.
Phase I trial of an oral vaccine
A Phase I clinical trial of an oral vaccine showed that it stimulated mucosal immune responses, and was safe. IgA antibodies were able to bind to a range of variants and demonstrated neutralising activity for at least six months. The vaccine, based on a non-replicating adenovirus, was well tolerated by participants. Forty participants were vaccinated. The paper has not yet been peer reviewed.
Pan-coronavirus vaccines in development
Wired magazine discusses the pan-coronavirus vaccines in development. It also describes “nano-traps” which are intended to capture viral variants following an earlier infection and destroy them by phagocytosis.
Relatively long lasting IgG responses to infection and vaccination
A small study of university students found that in the majority nucleocapsid protein-specific IgG antibodies became undetectable five months after infection. Spike-specific IgG was more stable, and its abundance increased after vaccination.
Only 22 students provided results for the whole seven month study. Participants were young and healthy, and had asymptomatic or mild infections, so the results are unlikely to be generalisable. The paper has not yet been peer reviewed.
Boosters provide protection against Omicron variants
Booster vaccine doses can provide protection against severe Covid from Omicron variants. Neutralising antibody levels increased substantially, as did activity against Omicron variants, after a third mRNA dose, or a combination of vaccines.
The time interval between vaccine doses may also be important, with a longer gap between doses potentially improving effectiveness. The paper was published in Science.
Good immune response in children after two Moderna doses
Children aged 6-to-11 developed strong humoral immunity after two doses of the Moderna vaccine. Strong binding to a range of variants was found. A 100 microgram vaccine dose (the adult formulation) resulted in stronger and more consistent binding of Omicron than a 50 microgram dose (the paediatric formulation). Responses to the vaccine were greater than those following an infection.
Immune responses were measured only up to four weeks after the second dose. Only 24 vaccinated children participated in the study. The paper was published in Science Translational Medicine.
Reinfection risk reduced after vaccination
The risk of reinfection after a prior infection was reduced by about half in people living or working in long term care facilities when the person is subsequently vaccinated. The risk was reduced by 62% in the general population.
The study involved 95,000 people, and estimated risk of infection within 9 months of an earlier infection. The study underestimated reinfections, since asymptomatic infections will have been missed. The paper was published in JAMA Network Open.
Non-vaccine-related papers
Rapid Antigen Tests being reviewed for effectiveness
Australia’s Therapeutic Goods Administration is reviewing all Covid-19-specific laboratory antigen tests and rapid antigen tests (RATs) to ensure they can detect the newest variants. Several tests have already been withdrawn from sale or distribution.
Length of infectiousness
A news article published in Nature summarises evidence for how long people with Covid-19 are likely to be infectious. The period of infectiousness varies between individuals. One study indicated that 25% of people may still be infectious after 8 days, and another indicated some may be infectious for 10 days. Five days is considered too short a quarantine period, with 10 days being preferable according to the article.
The specific variant, and the degree of vaccine or natural immunity an individual has, influence the infectiousness period. There is also some evidence that people taking Paxlovid may be infectious for longer if their infection rebounds during treatment.
Children may be less likely to become infected than adults
An Icelandic study found children are less likely than adults to become infected, and are less likely to develop severe Covid-19. Overall only 16% of infections occurred in those under 18. Incidence was higher in 14-to-17 year olds than younger age groups, and in the older group symptoms tended to last longer than in younger children.
Nearly three quarters of infections in children were recorded as mild. The Icelandic population is relatively homogeneous, so the results may nor be broadly applicable. The paper was published in The Pediatric Infectious Disease Journal.
Molnupiravir can be an effective treatment in older people
An Italian study found that early treatment with molnupiravir was effective in halting disease progression in elderly patients. Some of the participants were infected while in hospital for other conditions. The treatment did not prevent disease progression in 10% of the patients. Covid progression was more likely in patients with neurodegenerative disorders. Effectiveness was greater for those treated within three days of Covid symptoms appearing.
Participants had a mean age of 70 years. The paper was published in the Journal of Medical Virology.
Pandemic origin linked to seafood market
Two companion papers, both published in Science, provide further evidence of the pandemic originating in a Wuhan seafood market. Non-peer reviewed versions of these papers were included in the 4 March Tracker.
The first paper builds on earlier analyses of the earliest cases, and environmental testing for the virus in the market. It concludes that the earliest known Covid-19 cases (from December 2019) were geographically centred on the Huanan Wholesale Seafood Market, and that it is likely the virus emerged from the wildlife trade.
The second paper suggests, based on genome analyses, that there were several independent animal to human transmission events associated with the market.