The Pfizer vaccine provides strong protection against Covid symptoms and severe disease after two doses but markedly lower protection after a single dose, the first large-scale peer-reviewed study of the real-world effectiveness of the vaccine has found.
Separate survey data published by the Department of Health and Social Care (DHSC) found that for those over 80 who had received just a single dose of the Pfizer vaccine blood antibodies were relatively low at 34.7 per cent.
The study by Israel’s Clalit Research Institute was conducted in collaboration with researchers from Harvard University and published in the prestigious New England Journal of Medicine on Tuesday night.
It found two doses of the Pfizer vaccine reduced symptomatic Covid-19 by 94 per cent and severe disease by 92 per cent. A single dose reduced symptomatic Covid-19 by 57 per cent and severe disease by 62 per cent after three weeks.
The single-dose findings are lower than was reported by Public Health England for the Pfizer jab earlier this week for severe disease and may raise questions about the UK strategy of delaying the second dose of the Pfizer vaccine to 12 weeks. The vaccine’s makers say the second dose should not be delayed beyond six weeks and recommend three.
The antibody survey published by the DHSC and conducted by Imperial College London and Ipsos MORI gives a similar signal. After two doses of the Pfizer-BioNTech vaccine, the proportion of participants who tested positive for antibodies was high across all age groups (100 per cent in those under 30, and 87.9 per cent in those 80 and over). But for older adults who received a single dose, the proportion testing positive for antibodies was just 34.7 per cent in those aged 80 and over.
Clalit is Israel’s biggest health care provider, covering over 50 per cent of the population and the peer-reviewed study is the most comprehensive to date on the Pfizer vaccine. The study examined data on 600,000 vaccinated individuals in Israel, along with 600,000 carefully matched unvaccinated control subjects.
The vaccine effectiveness for preventing symptomatic Covid-19 proved consistent across age groups, including adults aged over 70. The study also evaluated subpopulations with different numbers of comorbidities and found indications that vaccine effectiveness for preventing symptomatic Covid-19 may be slightly lower for individuals with a higher number of comorbidities, although the difference was not statistically significant.
The fast-moving UK variant B.1.1.7 became dominant in Israel during the study period and so strongly confirms that the Pfizer vaccine protects against it.
The study’s lead author, Professor Ran Balicer of the Clalit Research Institute, said the study confirmed the findings of the original Pfizer trial and confirmed that the “nationwide vaccination campaign in Israel is effectively protecting individuals against the currently prevalent strains of the coronavirus”, allowing for the easing of restrictions there.
He added: “Our study provides single-dose vaccine effectiveness for only the first three weeks following the first dose, since almost everyone in Israel gets their second dose after three weeks. In the UK, people are waiting 12 weeks between doses, and our study does not provide any information on first dose vaccine effectiveness past the third week.”