As the vaccine is rolling out, it shows that it IS preventing infections....


UK study of health care workers provides evidence Pfizer/BioNTech vaccine protects against infection

A preprint was posted today on the Lancet site present results of a study investigating efficacy of Pfizer/BioNTech vaccine in health care workers in the UK.

This is part of the SARS-CoV-2 Immunity and Reinfection Evaluation (SIREN) study that followed a large cohort of UK healthcare workers from >100 hospitals during the pandemic to assess the effect of prior infection on protection agains re-infection, and was amended to look at vaccine efficacy in January 2021.

In this report, there are a total of 23,324 participants from 104 hospitals that participated. Of these, 8,203 (35%) had been previously infected based on antibody or previous PCR tests.

By February 5, 19,384 (83%) had already received one dose of the the Pfizer/BioNTech vaccine, and 1,605 (7%) received both doses, with the median length of time between doses of 23 days. 6% others received the AstraZeneca/Oxford vaccine and were not included in this analysis.

This analysis tracks COVID-19 cases arising between December 7, 2020 and February 5, 2021, with regular asymptomatic PCR testing of all participants supplemented by additional testing if reporting symptoms in between scheduled asymptomatic PCR testing dates.

They did a rigorous statistical analysis to assess the hazard of infection (symptomatic or asymptomatic) and compare between vaccinated and unvaccinated groups, while adjusting for various factors that might contribute to risk of infection and thus bias the comparison including infection rate by week, age, sex, hospital, ethnicity, co-morbidities, region, job, and patient contact. This makes the comparison of vaccinated to non-vaccinated more representative of the potential causal effect of vaccination.

Summary of their results:

• Almost 90% of HCW received the vaccine, so there was not evidence of substantial vaccine hesitancy in this population.

• There were at total of 977 new infections (rate of 14 per 10,000 person-days), with only 71 occurring 21 days after 1st dose (8 per 10,000 person-days) and only 9 occurring at least 7 days after second dose (4 per 10,000 person-days).

• This resulted in estimates of vaccine effectiveness in reducing risk of infection (symptomatic or asymptomatic) of 70% starting 21 days after first dose, and 85% starting 7 days after second dose. They did not specify the effectiveness after first dose but before second dose, which would be <70% but not clear how much lower.

• They note that the vaccine efficacy was higher in the group not previously infected (72% and 86%), suggesting the vaccine efficacy was lower in the previously infected group -- but there were so few infections in either vaccinated or unvaccinated in previously infected group that there is not enough data to reliably estimate the efficacy for previously infected groups.

• They found that the previously infected group overall had 90% lower infection rates than those who had not been previously infected, across both vaccinated and unvaccinated groups.

https://www.covid-datascience.com/post/uk-cohort-study-provides-validation-pfizer-biontech-vaccine-protects-against-infection