Q&A: Why new data on vaccine effectiveness and intervals is relevant to Ireland
Re-think is warranted on policy of not giving AstraZeneca vaccine to older people
GPs and practice nurses receive their second dose of the Covid-19 Moderna Vaccine at St Mary’s Hospital in the Phoenix Park, Dublin. Photograph: Dara Mac Donaill / The Irish Times
In tandem with scaled-up of vaccinations, more reliable data is emerging on how effective vaccines are. With the UK and Israel significantly ahead of others countries in administering the jab, it is no surprise the most telling indications are now emerging from these jurisdictions.
First up, it is important to stress the latest findings – an Israeli study in the Lancet and research by Public Health Scotland (PHS) and Public Health England (PHE) – provide a lot of reassurance on the Pfizer and Oxford-AstraZeneca vaccines; especially in terms of first dose benefits. Positive news on their benefits with older people has also emerged.
But they are also flagging significant evidence that may warrant a revision of approach; on duration between first and second doses, and on not recommending the AstraZeneca jab for people over 65 – in both instances this is relevant to Ireland.
In England, a study in healthcare workers under 65 found one dose of the Pfizer vaccine reduced the risk of catching the virus by 70 per cent – and 85 per cent after the second dose. The healthcare workers were tested for the virus every two weeks, so it picked up asymptomatic infections as well as those who had symptoms.
What are the overall findings?
The Israeli study found an 85 per cent reduction in symptomatic Covid-19 within 15 to 28 days with an overall reduction of infections, including asymptomatic cases detected by testing, of 75 per cent.
One dose of vaccine against Covid-19 in Scotland has cut hospital admissions by more than 85 per cent, according to the first data published on the impact of the UK programme. By the fourth week after receiving the initial dose, the Pfizer and AstraZeneca vaccines had reduced risk of hospitalisation by up to 85 per cent and 94 per cent respectively.
What are we to make of dose interval data?
Both vaccines are being given as single doses until up to 12 weeks. While there is trial data to support the gap for the AstraZeneca vaccine, there is none for the Pfizer vaccine, which was given as a second dose at three weeks.
The UK is only place in the world where it was decided to extend the period to 12 weeks in an effort to get more vulnerable people vaccinated with a first dose. The HSE decided to extend the interval between the first and second doses of the Pfizer vaccine from 21 to 28 days to spread the benefit of the vaccine to more people.
Worryingly the Public Health Scotland (PHS) study shows an apparent rise in hospital admissions among people given one dose of the Pfizer vaccine after 21 days. The numbers were very small, however, and there was uncertainty over their significance, say the researchers, who did not look specifically at “waning immunity”.
Though the effectiveness of the vaccines reduced over time, they underline numbers were consistent with a relatively constant protection of about 70 per cent in preventing severe illness and hospitalisations.
Ireland needs to re-think its strategy given these findings, according to UCC immunologist Dr Elizabeth Brint. It could be time to consider spreading out the time between administering the first and second dose of the Pfizer vaccine.
The Lancet data indicates the first dose of this vaccine confers much higher protection than previously thought. “In addition, emerging evidence shows that vaccination is indeed reducing transmission.”
She adds: “Therefore, surely it is time for a vaccination strategy rethink with a shift to a model more like what the UK is perusing, which is currently achieving good results, with more people receiving the first dose and spacing the second dose out more to, for example, nine to 12 weeks.”
Re-thinking the strategy is pertinent, she believes, in light of transmission rates remaining stubbornly high while, anecdotally, it appears public compliance with restrictions seems to be on the wane.
The UK evidence shows spreading out Pfizer doses to nine or even 12 weeks did work and there was “no reason to assume any drop in overall protection if the times between the first and second doses were spaced out further”.
Some scientists, however, point to the risk that extending the interval means weaker protection which increases the risk of “vaccine escape variants” emerging.
What of findings relating to older people?
Among over-80s vaccination was associated with an 81 per cent reduction in hospital admission risk in the fourth week, when the PHS results for both vaccines were combined.
The AstraZeneca vaccine appears to have performed very well in older people. Clearly, this could be cause for rethink in those countries that decided not to allow it to be used in over-65s because of a shortage of trial data.
PHE released the results of testing in the over-80s which found that 3 weeks after the first dose, the Pfizer vaccine was 57 per cent effective against symptomatic illness, whether mild or more severe.
Although not many people have had a second dose, the evidence suggested efficacy rose to 85 per cent in those who did. The data also shows people who have been vaccinated who catch the infection are much better protected against severe disease, hospitalisation and death.
In Ireland, the HSE decreed earlier this month that only the Pfizer and Moderna vaccines should be administered to over-70s, especially because of indication of reduced efficacy. These findings will prompt a re-evaluation of this approach.
So what is the best advice now?
The strong public health advice is to take whatever vaccine is offered, while the second dose remains a vital element of the vaccination programme. People should continue to follow all the public health advice, such as wearing masks and keeping apart, even when they have been vaccinated.
As more data comes in, there will be more precision on efficacy against different end-points – infection; mild-to-moderate disease, severe disease, hospitalisation, death and “long-Covid”.
If “herd immunity” is to be achieved through vaccination, vaccines need to prevent infection and transmission. These early data are the first to demonstrate real-world reductions in infection, which mean likely reductions in transmission.