The decision to favour the Pfizer-BioNTech and Moderna vaccines for the over-70s over the AstraZeneca jab makes the rollout of the vaccination programme to this next priority group in the vaccine queue more complicated. This is because the Pfizer and Moderna jabs require more complex handling.

Why are there difficulties around the rollout of Pfizer and Moderna vaccines?

These are the vaccines preferred by the State for the over-70s because of the proven data around their effectiveness in older people. The Pfizer vaccine is more complicated to handle but the State is getting roughly four times more of those than the Moderna jabs over the coming weeks.

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What’s so complicated about it?

The Pfizer vaccine is highly effective at preventing people getting seriously ill if they contract Covid-19, but managing, transporting, storing and administering the doses is more complicated and labour intensive.

The problem is that it must be stored at ultra-cold temperatures at between -80 and -60 degrees. It must then be transferred to vaccination sites within 12 hours and once it arrives and is defrosted, it has a limited shelf life of five days when stored in a fridge. Any hours used up transporting the vaccine at fridge temperature count against the five-day storage limit.

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Thawing to room temperature takes 30 minutes and once at room temperature, the vials only last another two hours. Once removed from a fridge, it must be gently inverted 10 times. It must then be diluted with 1.8ml of saline and then have 1.8ml of air removed from the vial before gently inverting the diluted vaccine 10 times again. You are not supposed to shake it.

After dilution, each vial contains up to seven doses of 0.3ml of the vaccine. The diluted vaccine can be stored at room temperature but must be used within six hours. They cannot be refrozen.

While being stored for those six hours, they should have minimal exposure to room light and no exposure to direct sunlight or ultraviolet light. The Pfizer vaccine gives people 95 per cent protection over two doses, 28 days apart.

How is the AstraZeneca vaccine easier to manage?

It can be injected by a GP or a pharmacist into a person’s arm straight out of a fridge. The first AstraZeneca vaccines, about 21,000 doses, are expected to arrive into the country this weekend, with hundreds of thousands more expected in the following weeks. The AstraZeneca vaccines, once they arrive, are expected to be used on remaining frontline healthcare workers, who are younger, so more Pfizer and Moderna vaccines would be available to the over-70s.

Is the handling of the Moderna vaccine as complicated as the Pfizer vaccine?

No, but the State is getting fewer Moderna vaccines.

It can be stored frozen at temperatures of between -25 and -15 degrees until expiry and in a fridge for 30 days or at room temperature for 12 hours.

Once the vaccine vial has been punctured, it must be used within six hours. A single dose of the vaccine is 0.5ml. Any unused or partially unused vials must be discarded. Two doses of the vaccine, 28 days apart, gives a person 94 per cent protection from serious Covid-19 illness.

How are these technical requirements affecting the rollout?

The Government and State health officials decided this week that Pfizer and Moderna vaccines, rather than the more easily stored AstraZeneca jab, should be given to people aged over 70 where possible. As a result the rollout plan has had to be reworked because a large part of the Government’s original plan and timetable involved older people getting the AstraZeneca vaccine.

This now means GPs managing smaller numbers of people will have to go to larger practices because of the challenges of transporting the Pfizer and Moderna vaccines. People will also be vaccinated at primary care centres and dedicated centres from February 15th when the over-70s start getting their jabs.

The Government is considering ways of getting older people such as the over-85s to vaccination locations and whether transport needs to be provided.

Minister for Health Stephen Donnelly has said that he is confident that 70 per cent of GPs will be able to provide the Pfizer and Moderna vaccines to patients in their own surgeries.

What are the difficulties in vaccinating at smaller sites?

In Israel, which has the best vaccine rollout rate in the world, it was found that there were not enough people in the top priority groups to be vaccinated at some smaller localities because Pfizer's initial specifications said that once the vials were removed from ultra-low-temperature freezers they had to be transported only in large trays containing 195 vials, or about 1,300 doses. Vaccinating at smaller sites would require repackaging vaccines in very low-temperature fridges for distribution in smaller numbers at more remote sites, which is what happened in Israel. In other words, the more people at a vaccination location, the easier it is to administer the Pfizer vaccines.

So how many vaccines are needed for this next group to be vaccinated?

There are about 480,000 people over the age of 70 who need to be vaccinated requiring 960,000 doses.

Supplies vary and the HSE has said that more doses could become available but under rough estimates the State expects 1.2 million vaccine doses by the end of March, including 800,000 Pfizer and Moderna jabs. That means there is expected to be a shortfall of at least 160,000 doses for the over-70s if the target completion date for that group at the end of March is to be met.

In other words, vaccinating the population’s next group, the over-70s, will take longer than expected. All this will make getting more people vaccinated more quickly all the more difficult.