Omicron variant papers

Higher rates of household infections for Omicron than Delta

The infection rate within households in Denmark was higher for the Omicron variant than the Delta in vaccinated people. Similar rates of infection were seen in both variants among unvaccinated household members, suggesting immune evasion rather than an inherently higher level of transmission is responsible for higher infection rates for Omicron.

Overall, the secondary attack rate for Omicron was 31%, compared with 21% for the Delta variant. Greater transmission was seen for unvaccinated household members, while those with three vaccine doses had a lower risk of being infected.  

In triple dosed individuals the secondary attack rate was three times higher for Omicron than Delta. The paper has not yet been peer reviewed.

Prior infection less effective in preventing Omicron infection

In Qatar a prior SARS-CoV-2 infection provided strong protection against symptomatic reinfection by Alpha, Beta and Delta variants, while protection against Omicron was lower. Protection was at least 85% for the Alpha, Beta and Delta variants, and 56% for Omicron.

The risk of hospitalisation following reinfection was low for all variants. In Qatar the population is relatively youthful, with only 9% over 50, so the results may not be generalisable. The paper has not yet been peer reviewed.

Generally lower severity of Omicron infections

Eric Topol in his Ground Truths newsletter summarises six studies demonstrating the effectiveness of vaccine T cell response against the Omicron variant.

The UK’s Health Security Agency 31 December Technical Briefing confirms lower rates of hospitalisations for the Omicron variant, and very reduced risk after three vaccine doses. It also notes that the very high levels of infectiousness for Omicron still leads to higher numbers of people in hospital with Covid.

In South Africa, there were fewer hospitalisations due to Omicron compared with earlier infection waves. The frequencies of severe cases and deaths due to Omicron were also lower. However, the age of hospitalised patients in the latest infection wave was much younger than in the third (Delta) wave - a median of 36 years compared to 59.proportionally more young people were hospitalised with Omicron. The paper was published in JAMA.

Reduced early interferon response may contribute to lower severity

The initial interferon response against the Omicron variant is lower than for the Delta variant, which may in part account for lower severity of Omicron infections. The Omicron variant was also as sensitive as Delta to 8 anti-SARS-CoV-2 drugs in lab tests. The paper is not yet peer reviewed.

Nasal rapid antigen tests may not detect Omicron soon enough

In a small study a rapid antigen test failed to detect Omicron infections for several days. Thirty people were tested daily with both PCR and a nasal rapid antigen test at the same time. It took about three days after a positive saliva PCR test for rapid antigen tests to return positive results. This appears to be due to viral loads rising more quickly in saliva samples than nasal ones.

This could mean that if only nasal rapid antigen tests are used, people may be infectious for several days before knowing. The paper has not yet been peer reviewed.

Vaccine-related papers

Vaccine safety in children under 12

Over 8 million doses of the Pfizer/BioNTech vaccine have been given in the US to children (5-11 years old), with very few serious adverse effects. Fatigue, headaches, and pain at the injection site were the most commonly reported reactions, and were more common after the second dose.

The study examined reports of adverse reactions submitted to the Vaccine Adverse Event Reporting System. Children received 10 microgram vaccine doses, instead of the 30 microgram doses given to those 12 and over. The paper was published in Morbidity and Mortality Weekly Report.

Developing an oral vaccine

An oral Covid vaccine is being developed based on a Salmonella vaccine platform. The vaccine incorporates the SARS-CoV-2 spike protein into an inactivated Salmonellabacterium strain. It was found to be non-cytotoxic for cell lines, and in mice stimulated SARS-CoV-2-specific immune responses. Further development is underway. The paper was published in Vaccine.

Viable virus levels in vaccinated people can be lower than in unvaccinated people

A small US study found that while viral loads were similar in vaccinated and unvaccinated people, those who were vaccinated had lower levels of viable virus in nasopharyngeal samples. While 40% of samples from unvaccinated people produced viral particles that could be cultured in cells, only 21% of vaccinated samples did. This suggests that vaccinated people may have a lower risk of infecting others.

Vaccinated participants had received two doses of the Pfizer or Moderna vaccines. Beyond five months after the second dose there were significant increases in culturable virus, indicating waning immunity. The paper is not yet peer reviewed.

A million deaths potentially prevented due to vaccinations in the US

Analysis and modelling of the pandemic in the US estimates that without their vaccination programme a million more deaths and 10 million more hospitalisations could have occurred during 2021. There could also have been 35 million more infection cases, largely due to the Delta variant in the US summer/autumn period.

The model assumes schools and businesses remained open and increased social activity in the second half of the year during the Delta wave. It also doesn’t take account of increases in preventable non-Covid deaths as a consequence of overwhelmed healthcare systems. The report is not peer reviewed.

Non-vaccine-related papers

Autoantibodies generated by infections

Antibodies that attack the person’s own tissues and organs (called autoantibodies) can be produced following infections from viruses and bacteria. A study reports that females may be more likely than males to generate autoantibodies after an asymptomatic SARS-CoV-2 infection, but the opposite may occur for symptomatic infections. There were also differences in autoantibody symptoms between women and men. The autoantibodiy reactions persisted for up to 6 months, and may be a cause for some cases of long Covid.

Comparisons were made between 177 infected adults and 53 people assessed before the pandemic. However, the demographic profiles of the two groups differed, the pre-pandemic data was obtained from healthcare workers in Germany while the infected subjects were from the US, and sample sizes were small, so the conclusions may not be definitive. The paper was published in the Journal of Translational Medicine.

Airborne transmission in NZ MIQ facility

Airborne transmission of the Delta variant following fleeting indirect contacts in an Auckland MIQ facility are described in a paper published in Emerging Infectious Diseases. Genome sequencing and security camera footage indicated that the infections occured between non-adjacent rooms from a single infected guest when room doors were simultaneously but briefly opened.

These transmission events were described in the media last year, but the paper provides a good case study of the longer range airborne mode of transmission for the virus.

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