Scientists have called for the Government to open up the vaccine programme to younger people to immunise more people against Covid-19 as the more contagious Delta variant spreads.
Dr Anne Moore, a vaccine expert at University College Cork, said younger people should be offered any available AstraZeneca and Johnson & Johnson jabs once they are made aware of the very low risk of blood-clotting as a side effect so that more people can be protected.
“We really are in a race at this stage and, if possible, we should open up the immunisation logistics to allow people of any age to register and to be vaccinated as soon as possible,” she said.
Kingston Mills, professor of experimental immunology at Trinity College Dublin, said that it would be “sensible” to administer the one-dose J&J jab to younger people who account for a large majority of the new Covid-19 cases given the low risk from blood clotting side effects.
Newly published research this week has shown the effectiveness of mixing vaccines. Prof Mills said that giving people a "primer" first dose of the AstraZeneca with a follow-up booster dose of the Pfizer vaccine has resulted in a "dramatically enhanced" antibody response.
“There is little rationale for confining it to the over 50s or the over 60s. If they are going to use it, they should use it in the whole population,” he said of the spare AstraZeneca vaccines.
Prof Mills said the Government had contained the pandemic in terms of protecting people against disease and that now it had to prevent the transmission of the virus; this meant vaccinating people in the 18- to 24-year-old age group where transmission rates are highest.
“It might be sensible to vaccinate those now especially with any available spare vaccine. That seems to me to be an ideal cohort to give it to,” he said.
He advised that if the Government has substantial spare vaccines available, they should “just get it out as quickly as possible and stop the transmission of the virus.”
However, not everyone agrees. Sam McConkey, a professor of infectious diseases at the Royal College of Surgeons in Ireland, said the Government should stick to its strategy.
"Moderna or Pfizer; if we got a large number of mRNA vaccines that would be preferable," he said, "I'm not sure it should be a priority for us to change our national guidelines to AstraZeneca."
The Delta strain of the virus is now accounting for one-fifth of Irish cases, and rates are expected to keep rising, as pointed out in Brussels by Taoiseach Micheál Martin.
A Public Health England paper last month found both the Pfizer and AstraZeneca vaccines are highly effective against the variant after two doses, but only 33 per cent three weeks after the first.
Prof McConkey pointed to a key difference; that Pfizer offered 88 per cent protection against symptomatic disease after the second dose, compared to just 60 per cent with AstraZeneca.
Based on that, he argued, the Government strategy up to now of using Pfizer or Moderna mRNA on younger people over AstraZeneca should remain the case, if possible.
UCD virologist Dr Gerald Barry said supply should influence decisions. While mRNA is preferable, AstraZeneca could be appropriately used on younger people, if the only vaccine available.
The risk of clots amongst young people from AstraZeneca is small compared with the risk posed by the more contagious Delta variant, said Dr Barry: “That’s the risk equation that they are weighing up,” he said.
Dependent on supply
However, he continued: “If it was the case that we only had to pause for two or three weeks then that’s a different question. If there was only a two- or three-week delay, you would be better waiting.”
Second doses of mRNA vaccines are given more quickly than AstraZeneca ones – about three to four weeks for the former, compared to eight weeks for the latter.
“The quicker you get your double shot the better,” Dr Barry said, but continually-changing vaccine messaging creates a communications challenge to get the benefits for younger people across, he said.
“I would always favour the mRNA vaccine in this age group as much as is possible,” he said, “/[but/] if it’s the only thing on the table, then AstraZeneca is the one to go for.”
Eighty-four per cent of new infections are now amongst those aged 45 and younger. The National Immunisation Advisory Committee (Niac) is now considering AstraZeneca's future use.
The use of the vaccine has varied considerably across the European Union, mostly due to earlier concerns around small numbers of associated blood clottings.
More than a dozen countries have at one time suspended its use, before later resumption. Some, including France, the Netherlands and Germany, have set a minimum age.