• During an online WHO briefing, scientists in South Africa said that a previous infection with SARS-CoV-2 appears to give little immunity to the Omicron variant, based on routine epidemiological surveillance data – which leaves more than 260 million people who have recovered from COVID-19 at risk for reinfection. Source

• Scientists say that they may have found a key step in how the Oxford/AstraZeneca coronavirus vaccine may cause an extremely rare but serious blood-clotting disorder. Their findings point to the adenovirus vector, which the vaccine relies on to deliver the spike protein gene into cells. The J & J coronavirus vaccine, which also relies on adenovirus, has also been linked to the same rare clotting disorder.

Researchers suggest that if the adenovirus leaks from muscle tissue into the bloodstream and binds to a clotting protein, it can trigger an antibody response that causes platelet clusters – a rare side effect that has occurred in 1 of every 100,000 first doses of the vaccine in the UK. One of the researchers, Professor Alan Parker of Cardiff University’s School of Medicine, said, “With a better understanding of the mechanism…there is an opportunity to engineer the capsid, or outer shell of the vaccine, to prevent this.” Sources 1,2

• A pre-print publication analyzed routine surveillance data from South Africa, covering 2,796,928 people with confirmed SARS-CoV-2, occurring at least three months before 27 November 2021. People with two positive test results at least 90 days apart were suspected to be reinfected. They reported that reinfection risk did not increase after the introduction of the Beta and Delta variants. In contrast, in October of 20201 they saw first infections dip and reinfections increase, leading them to estimate that Omicron reduced immunity from previous infection by half, noting “clear, population-level evidence to suggest substantial immune evasion by the Omicron variant.” Source

• Germany announces new nationwide restrictions for the unvaccinated; they will be prohibited from many public places, including bars, restaurants, and shops (except for pharmacies and grocery stores). Source

• Cases of the Omicron variant are detected in California, Colorado, Hawaii, Minnesota, and New York. Source

• France reports its first Omicron case amidst of a surge of the Delta variant that has driven cases to a daily high of 50,000. “We need to anticipate – there are still a lot of uncertainties,” said Jean-François Delfraissy, the head of the French government’s COVID-19 scientific advisory council, “But let’s not fight the wrong fight. The real fight, the real enemy, is the fifth wave with the Delta variant.” Source

• The European Centers for Disease Control and Prevention releases a report on the implications of Omicron for the region, noting that as of 1 December, 70 confirmed cases have been reported by 13 European Union and European Economic Area (EU/EEA) countries, most with a history of travel to southern African, although some countries are reporting community transmission.

The report warns that despite uncertainty and limited evidence on Omicron, there is a high probability of the variant spreading in EU/EEA countries, and its impact may be very high, since Omicron may cause a significant decrease in vaccine effectiveness – including protection against severe disease – and an increased risk of reinfections. It recommends a multi-layered approach, including prioritizing unvaccinated people for inoculation, consideration of boosters, initially for people ages 40 and over, then to people ages 18 and over as well as non-pharmaceutical interventions. Source

• Some experts theorize that the Omicron variant might have emerged from a human virus that passed from animals back to people. Robert Garry, a professor of microbiology and immunology at Tulane Medical School, says that seven of the mutations that allow SARS-CoV-2 to infect rodents are present in Omicron. Although he is unsure how Omicron evolved, he believes rodents would be the culprit for human-to-animal-to-human transmission. Michael Worobey, a professor of evolutionary biology at the University of Arizona, says that chronic SARS-CoV-2 infection in rodents (as has been occurred among immunocompromised people who developed multiple mutations), would make the idea of evolution within an animal host more likely. Source

Lancet publishes results from the 2,878- person phase II COV-BOOST trial, which compared safety and immunogenicity of different coronavirus boosters given to people who had already received two doses of the Oxford/AstraZeneca or the Pfizer/BioNTech vaccines. Study participants were split into three groups; Group A received a full or half dose of an experimental protein-based coronavirus vaccine from Novavax versus a control vaccine; Group B was boosted with a full or half-dose of the Pfizer/BioNTech vaccine, a full or half-dose of an experimental adjuvanted, inactivated virus-based coronavirus vaccine from Valneva, a dose of the J & J coronavirus vaccine or a control, and Group C received booster with the Moderna coronavirus vaccine, an experimental mRNA vaccine from CureVac, a half-dose of the Pfizer/BioNTech vaccine, or the control vaccine.

People who initially received the Oxford/AstraZeneca vaccine had varying immune responses to their boosters. Overall, neither a half or full dose of the Valneva vaccine was effective, while a booster dose of the Oxford/AstraZeneca vaccine did not produce a significant increase in cellular immune responses; the Moderna booster induced the highest level of immune responses.

Among people who received the Pfizer/BioNTech vaccine, half-and full-dose Valneva boosters did not increase antibody or cellular immune responses.

All other vaccines increased antibody responses. An Oxford/AstraZeneca booster significantly boosted cellular immune responses, while a full or half dose of the Novavax vaccine did not. All other vaccines increased cellular immune responses.

Notably, more side effects – most frequently fatigue and pain – were reported among people who got a Moderna booster after two doses of the Oxford/AstraZeneca and Pfizer/BionTech vaccines, and among people who got a J & J or Oxford/AstraZeneca booster after two doses of the Pfizer/BionTech vaccine.

The authors noted that their data “…endow immunisation advisory committees and policy makers with additional immunological and reactogenicity information, which will allow flexibility to deploy heterologous or homologous third doses after initial ChAd or BNT vaccines. These decisions will also be based on clinical, logistical, and supply considerations, targeted to the populations at greatest need.” Source

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