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Explainer: Why you may have a second dose vaccine appointment sooner than recommended

The HSE says that a 17 day gap for Pfizer is “safe and effective”.
Jul 29th 2021, 8:01 PM 51,605 19

THE HSE HAS moved to reassure people receiving a second dose of a Covid-19 vaccine sooner than the recommended interval between doses that it is “safe and effective”. 

The roll-out of Covid-19 vaccine has ramped up further in recent weeks with anyone aged over 18 now available to register for a vaccine and those aged 16 to 18 soon to be eligible. 

Less than a month ago, people in their early 30s became eligible to register and some in that age group have now had a first jab and have also been called for a second dose.  

Pfizer has accounted for over two-thirds of the total 5.7 million jabs administered in Ireland so far. 

Under the HSE’s clinical guidance, the recommended interval between doses of Pfizer is 21 to 28 days, with NIAC also saying that the “standard interval” is three to four weeks.  

The HSE also states on its website that the “minimal interval” between Pfizer doses is 17 days, with any second doses delivered before 17 days considered “invalid”. 

“If a dose is given between 17 and 27 days, this is considered a valid dose,” the HSE’s website states. 

Confusion over what is considered a “valid” interval and “recommended” interval has caused a number of people to query why they are booked in for a second dose slot less than three weeks after their first dose. 

In some cases, second doses are being booked for 17 or 18 days after the first dose. 

In a statement to The Journal, the HSE confirmed it is preferable to have a second dose of Pfizer within three to four weeks after the first dose but that the pace of the roll-out has brought the timeline forward in some instances:

We strive to deliver all second doses of Covid-19 vaccines between 21-28 days after the first dose, however for operational reasons and due to the pace of the rollout we are in a position to offer the second dose after 17 days in some cases. Second doses within this widow are clinically safe and effective.

Speaking to The Journal yesterday, NIAC chair Professor Karina Butler said that “the usual interval is three to four weeks” but that the licensed range is “three to six weeks”.

Other two-dose vaccines

In the case of Moderna, the other mRNA Covid-19 vaccine licenced for use in the EU, the recommended interval between doses is 28 days while the minimum interval is 24 days.

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For Oxford/AstraZeneca, a viral vector vaccine, the interval between doses is 4-12 weeks but four weeks is seen as preferable due to the need to vaccinate people quickly to counter the Delta variant. 

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Rónán Duffy


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