Distribute all doses first: study

Two studies and an article published Tuesday in a medical journal find that getting as many first vaccine doses into as many arms as possible is the most effective way to stem the spread of COVID-19.

One finds the practice of reserving half the vaccine doses received for the second dose, as is being done by Nova Scotia, is statistically less effective than using them all upfront to get partial immunity in as many people as possible and relying on the supply chain to come through with the second doses.

“I would say it is less urgent (in the case of Nova Scotia where COVID-19 cases remain low) but it still makes sense,” said Ashleigh Tuite, lead author of Alternative Dose Allocation Strategies to Increase Benefits From Constrained COVID-19 Vaccine Supply published in the academic journal Annals of Internal Medicine.

The Pfizer-biontech MRNA and the Moderna MRNA vaccine require two doses to reach over 94 per cent protection against COVID-19.

Provinces outside of Atlantic Canada that have been experiencing significantly higher rates of infection (including Ontario and Quebec) have dropped the practice of keeping a second dose in reserve for every first dose delivered.

During a technical briefing on Tuesday afternoon, Department of Health staff confirmed that Nova Scotia is continuing with this practice so long as case counts stay low.

The official said that our successes in stemming

transmission through social distancing and contact tracing allow us to take a conservative course that ensures the vaccines are delivered in accordance with manufacturers' directions — a second dose after 21 days for the Pfizer vaccine and 28 days for the Moderna.

Tuite, an infectious disease epidemiologist at the University of Toronto, created a mathematical model that shows 23 to 29 per cent of COVID-19 cases would be averted if 90 per cent of the available of doses are distributed immediately, with only 10 per cent kept in reserve.

Her analysis presumes a population with widespread community transmission — something we have managed to avoid — and the capacity to get all the available vaccines in arms as soon as they arrive.

During the technical briefing, officials said accelerated vaccine delivery remained an option if a steep upsurge in case counts required it.

In the meantime, the province is proceeding with its phased approach — aiming to get 140,000 doses into the arms of health care workers involved directly with patients, long term care residents, staff and caregivers, residential care residents and staff and Nova Scotians 75 or over by the end of April.

Phase two begins in May and will seek to target remaining health care workers and essential workers (currently being defined).

Phase three will see the vaccine become available to all Nova Scotians.