Vaccine-related papers

Impact of vaccination on transmission

A UK study found that the Pfizer/BioNTech and AstraZeneca/Oxford vaccines reduce transmission within households. Effectiveness against transmission was 42% for AstraZeneca and 31% for Pfizer.

Both vaccines were more effective in preventing transmission of the Alpha variant than the Delta. This was based on an analysis of 195 households. The paper has not yet been peer reviewed.

Viral dynamics in vaccinated & unvaccinated athletes

A study of viral dynamics in NBA players and staff found no differences between infected vaccinated and unvaccinated participants. Mean peak viral load and the number of days the virus was detectable were not significantly different between vaccinated and unvaccinated subjects.

As found in other studies, there was a high degree of variation among individuals. The study had a relatively small number of participants, and all were healthy young men so the results may not be generalisable. The paper was published in The New England Journal of Medicine.

Increased dose interval generates stronger antibody responses

A US study found a 42–49 day interval between mRNA vaccine doses generated higher antibody concentrations than a 17-28 day interval. Similar effects were seen for both the Pfizer/BioNTech and Moderna vaccines.

The study involved 186 vaccinated participants,with antibody levels measured about 56 days after the second dose. Participants were paramedics, who were mostly white and generally in their mid-to-late thirties, so aren’t representative of the general population. The paper is to be published in Clinical Infectious Diseases.

Comparing infection risks of two vs three vaccine doses

An Israeli study of over 300,000 adults found the risk of infection was much lower for those who had had three vaccine doses than two. Three-dose participants were matched with similar two-dose recipients, and ages ranged from 40 to over 80. For those who had received three Pfizer/BioNTech doses they were 86% less likely to become infected when assessed 28 to 65 days after the third dose.

The impact of third doses on hospitalisation risks requires further study. The paper was published in JAMA Internal Medicine.

A new version of the Moderna vaccine generates similar immune responses as the original in mice

Both the original Moderna vaccine and a version (mRNA-1273.351) designed for the Beta variant provided similar levels of protection against a range of variants in mice, and both were weakest against the Delta variant.

This is different from mRNA-1273 results in people. It may reflect differences in the immune systems of mice and people, and trials of the modified vaccine on human cells and people are required. The paper was published in Science Translational Medicine.

Adenovirus-based vaccines bind to a molecule associated with blood clotting

The adenovirus-based vaccines (AstraZeneca/Oxford, and Johnson & Johnson/Janssen) bind to Platelet factor 4, which may explain their association with a slightly increased risk of blood clots. Platelet factor 4 has previously been shown to be associated with heparin-induced thrombocytopenia. Binding with the vaccine could lead to several blood system responses, which require further study. The paper was published in Science Advances.

Modelling the impact of vaccination in New Zealand

A model of the effect vaccination rates have on transmission in New Zealand finds that there can be a dramatic decline in infections when vaccination rates go from 20% to 80%. The model also estimates that unvaccinated individuals are 3.3 times more likely to become infected, and 25 times more likely to be hospitalised compared with fully vaccinated individuals.

The model assumes the vaccine is 70% effective against infection. It also assumes vaccinated and unvaccinated people have equal exposure risks. Other public health measures are not included in the model. The paper has not yet been peer reviewed.

In a separate paper, the same model shows that infections are largely spread by unvaccinated people. A vaccinated traveler with COVID-19 is 9 times less likely to seed an outbreak than an infected unvaccinated traveler. If 90% of those over 12 are vaccinated, then a vaccinated person is 1.9 times more likely to be infected by an unvaccinated person than a vaccinated person even though there are nearly four times as many vaccinated people. The paper has not yet been peer reviewed.

Measuring neutralisation activity

A review looks at the different types of neutralisation tests and their uses on different vaccines and viral variants. It notes that the variety of tests available makes it difficult to compare studies. The paper was published in npj Vaccines.

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Source: https://smcnz.substack.com/p/coronavirus-research-tracking-3-december