Oxford-led COVID vaccine shows sustained 90-day protection of 76%

Doctor giving COVID vaccine to senior woman

Researchers at the University of Oxford have today published in Preprints with The Lancet an analysis of further data from the ongoing trials of the vaccine.

The data reveal that the vaccine efficacy is higher at longer prime-boost intervals, and that a single dose of the vaccine is 76% effective from 22 to 90-days post vaccination.

Development of the vaccine was funded by UKRI and the Department of Health and Social Care through the National Institute for Health Research (NIHR), as part of the joint rapid research response.

Further, the publication reveals:

  • single standard dose efficacy of 76% is achieved from day 22 to day 90 post-vaccination with protection not falling in this three-month period
  • after the second dose, efficacy rises to 82.4% with the 3-month interval being used in the UK (82.4% effective, with a 95% confidence interval of 62.7% – 91.7% at 12+ weeks)
  • data supports the 4-12 week prime-boost dosing interval recommended by many global regulators
  • analyses of polymerase chain reaction (PCR) positive swabs in UK population suggests vaccine may have substantial effect on transmission of the virus with 67% reduction in positive swabs among those vaccinated.

Read the paper in Preprints with the Lancet

Vaccine efficacy higher with longer interval

In this preprint, which is currently under review at The Lancet, they report on an analysis of additional data to include information from the trial up to the 7th December 2020. This includes a further 201 cases of primary symptomatic COVID-19 (332 cases from 131 reported in previously).

They report that the effect of a dosing interval on efficacy is pronounced. Vaccine efficacy rises from 54.9% with an interval of less than six weeks to 82.4% when spaced 12 or more weeks apart.

Sustained protection after first dose

They also detail that a single standard dose of the vaccine is 76% effective at protecting from primary symptomatic COVID-19 for the first 90 days post vaccination. Twenty-two days after the vaccination, the immune system has built this protection, and it shows little evidence of waning in this period.

The exploratory analyses presented in this preprint suggest that it is the dosing interval and not the dosing level that has a great impact on the efficacy of the vaccine. This is in line with previous research supporting greater efficacy with longer prime-boost intervals done with other vaccines such as:

  • Influenza
  • Ebola
  • malaria.

Reduction in transmission of virus

The authors also report further on the potential for the vaccine to reduce transmission of the virus. Swabs obtained from volunteers in the UK arms of the trial show a 67% reduction after the first dose of the vaccine.

They also hope to report data regarding the new variants in the coming days and expect the findings to be broadly similar to those already reported by fellow vaccine developers.

Professor Andrew Pollard, Chief Investigator of the Oxford Vaccine Trial, said:

These new data provide an important verification of the interim data that were used by more than 25 regulators including the Medicines and Healthcare Products Regulatory Agency (MHRA) and European Medicines Agency (EMA) to grant the vaccine emergency use authorisation.

It also supports the policy recommendation made by the Joint Committee on Vaccination and Immunisation (JCVI) for a 12-week prime-boost interval, as they look for the optimal approach to roll out, and reassures us that people are protected from 22 days after a single dose of the vaccine.

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