Professor Justin Stebbing in his weekly science update looks at the current research.  

The risk of asymptomatic SARS-CoV-2 infection is significantly lower amongst patients who had received at least one dose of the mRNA COVID-19 vaccine compared to an unvaccinated patient.  

This was based on a retrospective cohort study of asymptomatic adult patients across multiple US states undergoing a pre-procedural SARS-CoV-2 molecular screening test. 

SARS-CoV-2 was detected in 3% of the unvaccinated patients compared to 1% of participants who had received at least one dose prior to screening.  

After adjusting for age, sex, race, ethnicity and location, the risk of a positive test was significantly lower for patients who had received their first dose greater than 10 days earlier and those who had received their second dose greater than naught days when compared with the unvaccinated patients. 

This was highlighted in the Oxford Academic Clinical Infectious Diseases accepted manuscript by Tande published on 10th March 2021.  

The results of their study demonstrated the impact of the vaccines on reduction in asymptomatic infections, supplementing the randomised trial results on symptomatic patients.  

According to the CDC published by Britain and others on March 19th, a retrospective cohort analysis in two Connecticut skilled nursing facilities found partial vaccination with the Pfizer BioNTech COVID-19 vaccine from more than 14 days after the first dose through to seven days after the second dose was 63% effective against SARS-CoV-2 infection.  

These skilled nursing facilities experienced outbreaks from December 2020 to February 2021.  

The study confirmed that partial vaccination with the Pfizer BioNTech COVID-19 vaccine was associated with a significant reduction in the risk for SARS-CoV-2 infection amongst these skilled nursing facility residents.  

The results, coupled with the findings from a previous study amongst comparable older adult populations in Israel which reported more robust protection after the second dose, suggest that complete two-way vaccination is an important strategy for preventing COVID-19 in this affected population.  

Reassuring evidence from a longitudinal cohort study of healthcare workers in England showed that both natural infection and vaccination with two doses of the Pfizer BioNTech or Oxford-AstraZeneca vaccine provided more than 85% protection against symptomatic and asymptomatic SARS-CoV-2 infection including the B.1.1.7 variant, the so called UK Kent variant.

Both natural infection resulting in detectable anti spike antibodies and two vaccine doses provided robust protection.  

None of the healthcare workers who had received both doses had symptomatic infection and incidence was 98% lower amongst the seropositive healthcare workers and the incidence of any PCR positive result with or without symptoms was reduced by 90% and 85% with or without symptoms respectively. 

Single dose vaccine was slightly less effective and reduced the incidence of symptomatic infection by 67% and any PCR positive result by 64%.  

The London General Practice commends the National Health Service on its vaccination programme and encourages all those called for vaccination to take up the offer and looks forward to the day that all populations have been vaccinated.  

The Johnson & Johnson Novavax vaccine has published encouraging data in a phase three trial in the UK, an efficacy of 96.4% was indicated against mild, moderate and severe disease caused by the original SARS-CoV-2 strain. 

In South Africa, the company announced final results of its phase 2B trial with an efficacy of 55.4% amongst HIV negative trial participants in a region where the vast majority of strains were the B.1.351 variant.  

Across both trials, Novavax demonstrated 100% protection against severe disease including all hospitalisations and deaths.  

In Israel, effectiveness of the Pfizer BioNTech vaccine gradually increased starting at 12 days after the first vaccine dose and plateauing to around 35 days according to a large analysis of electronic health records from 1.79 million individuals in Israel.  

According to the preprint published by Yellen and others in medRxiv, effectiveness was uniform for men and women yet declined mildly but significantly with age and for patients with specific chronic comorbidities, notably type 2 diabetes.

Dr Paul Ettlinger

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