A Covid-19 jab also opens the way to a vaccine bonus, with more signs about the possibility of restarting foreign travel some time in the summer.

The revamped plan has some old and new elements which will impact how soon people will get a jab and also change the type of vaccine they will get.

Age before youth

At the centre of the new plan is a decision to proceed down the queue for vaccines based on age. People in their 60s who registered over the past two weeks are now being invited for a vaccine.

From today, people in their 50s can apply, beginning with those aged 59, working its way down by each year over the coming days. Both these age groups are vulnerable to serious illness if they get Covid-19.

Vaccine selection

The reason for the overhaul of the plan is due to recent decisions by the National Immunisation Advisory Committee (Niac) which assessed the one-jab Johnson & Johnson vaccine. This was in light of a very small risk of a rare blood clot. It recommended it be confined to people over 50.

It also looked again at the AstraZeneca vaccine, which is linked to a small risk of blood clots, and said its previous decision to confine it to over-60s should change. The vaccine could also be given to people in their 50s. This meant that these two vaccines could not be given to people under 50.

The question was whether the HSE should just give the AstraZeneca and Johnson & Johnson vaccines to people in their 50s and 60s, while administering the Pfizer and Moderna vaccines to the under-50s.

Supply hurdle

There are no neat solutions to vaccine roll-out and it all comes back to supply. If the HSE decided to confine people in their 50s to the Johnson & Johnson vaccine alone, it could have been well into June, which would coincide with the substantial delivery of 600,000 doses promised this quarter.

That would leave a vulnerable age group waiting. In the meantime, supplies of Pfizer, Moderna and hopefully AstraZeneca vaccines would be arriving.

Should people in their 50s be asked to wait while the HSE started vaccinating people in their 40s or 30s before them with Pfizer and Moderna jabs?

Mixing it up

The new plan will see much more flexible use of vaccines. The rules about confining AstraZeneca and Johnson & Johnson vaccines to the over-50s are likely to be relaxed.

The HSE plans to offer the other vaccines based on availability. So, people in their 50s can also be offered the Pfizer or Moderna vaccines.

It means people in their 50s will not face any extended delay they might have encountered if they had to wait for supplies of Johnson & Johnson in June.

Next in queue

After people in their 50s are vaccinated, the portal will open to those in their 40s and then proceed to the younger age groups. What makes the new plan different for the under-50s is that they will be offered the vaccines that are available. None will be off-limits.

They include the AstraZeneca and Johnson & Johnson vaccines which, according to Niac advice, should be confined to over-50s. However, it states that the benefits of the vaccines outweigh the extremely low risks of unusual blood clots.

It allows for use of the vaccines in the under-50s, where alternatives were not available. In the UK, the cut-off for the AstraZeneca vaccine is under-30.

There may be more precise guidelines around giving these two vaccines to younger age groups when it comes to the time.

Speeding up roll-out

There is some debate around whether it would have not been just practical, but also more effective in giving vaccines to younger age groups earlier.

More than three quarters of people who are testing positive now are under 45 and the argument is that if more were vaccinated, they would be less likely to spread the virus.

Jabs for younger age groups

More needs to be known about how much the vaccines block transmission. It is clear they protect people from getting very sick if they catch Covid-19, so it would make more sense at this point to give the vaccine to older age groups who are more susceptible to the ill effects of the virus.

As the country opens up, the risks of infection increase for the unvaccinated.

The new plan should not make much difference to the overall expectation of when younger people are offered the vaccine. Much depends on expected deliveries arriving here over May and June.

The aim remains to have around 82pc of the adult population with at least one vaccine dose by the end of June.

The power of vaccination is becoming more clear in countries that are ahead of us. In the UK there has been talk of ending physical distancing later in June, although this idea has been rejected by public health experts. People are also looking ahead and scientists say vaccines should be rolled out to the adult population as soon as possible.

These should be followed up by booster doses to protect against new variants of the virus. These new variants remain a threat and can make existing vaccines less effective. There is still a fear that one or more of these variants could lead to another wave in the autumn.

Visit our Covid-19 vaccine dashboard for updates on the roll out of the vaccination program and the rate of Coronavirus cases Ireland