Pfizer Covid jab ‘effective at preventing hospital admission for at least six months’

‘Pfizer jab effective at preventing hospital admission for at least six months’. Picture: Yui Mok/PA

The Pfizer Covid vaccine is highly effective at preventing hospital admission even with the Delta variant, new research shows – though its effectiveness against infection almost halves after six months.

Two doses of the jab are 90% effective against Covid-19 hospital admission for all variants for at least six months, according to the study.

But effectiveness against infection fell over the study period, dropping from 88% within one month after receiving two vaccine doses, to 47% after six months.

Looking at specific variants, researchers found that the reduction in vaccine effectiveness against infection over time are probably due to waning immunity, and not the Delta variant escaping the protection offered by the jab.

The campaign to deliver a third dose of the Covid-19 vaccine to medically vulnerable groups will begin this week, HSE chief executive Paul Reid has said. 

Appointments are likely to be made from Wednesday, with the third dose administered to those who are immunocompromised and over the age of 12 on Friday.

Mr Reid said contact would be made with those who are deemed at highest risk, adding that risk would be determined by clinical teams, focusing on the most vulnerable groups.

The researchers say the new  US study highlights the importance of improving vaccination rates worldwide and monitoring vaccine effectiveness to determine who should be prioritised for a booster dose.

Dr Luis Jodar, senior vice president and chief medical officer, Pfizer vaccines, said: “Our variant-specific analysis clearly shows that the BNT162b2 vaccine is effective against all current variants of concern, including delta.

“Covid-19 infections in people who have received two vaccine doses are most likely due to waning and not caused by delta or other variants escaping vaccine protection.”

Researchers analysed 3,436,957 electronic health records from the Kaiser Permanente Southern California (KPSC) health system between December 4, last year, and August 8 this year.

During the study period, 5.4% of people were infected with coronavirus,

Among those who were infected, 6.6% were admitted to hospital, and the average time since being fully vaccinated was between three to four months.

An analysis of 8,911 positive tests found the Delta variant made up 28% of the overall proportion of positive tests.

According to the study, the Pfizer jab was 93% effective against Delta variant infections one month after two doses but fell to 53% after four months.

Effectiveness against non-Delta variants was 97% one month after receiving two doses, and fell to 67% after four months.

Meanwhile, effectiveness against Delta-related hospital admissions remained high (93%) for the duration of the study period.

The researchers did not see a difference in waning between different variants.

The US study, conducted by Kaiser Permanente and Pfizer, is published in The Lancet.