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Pfizer vaccine delivers encouraging first results in Israel — Two studies

Early findings from Israel’s COVID-19 vaccination programme suggest that the rollout of the Pfizer BioNTech vaccine is leading to fewer new infections and is at least 50% effective 13 to 24 days after the first dose.

Israeli Ministry of Health figures found that only 531 people out of almost 750 000 fully vaccinated over 60 year olds tested positive for COVID-19 (0.07%). Of these, just 38 were hospitalised with moderate, severe, or critical disease.

The ministry analysed the records of nearly 1m people between their first vaccine dose to at least seven days after the second dose. They found that there were three covid-19 deaths in vaccinated over 60s, but said it was possible they contracted the virus at an earlier stage before their immunity had time to build up.

In the period before the protection took effect, over 7,000 infections were recorded, with just under 700 cases of moderate to critical illness and 307 deaths. No time scale or age group for these figures was given. The Ministry of Health said that the current data indicated that new cases and illnesses fell consistently from 14 days following the first dose.

Currently Israel has vaccinated more than 3.1m people, 1.8m of whom have received a second dose. Notably the country is not vaccinating certified recovered covid-19 patients, although the Ministry of Health website does not provide information on how someone is certified to have recovered.

The website states that “there isn’t enough information about the period of time during which a recovered coronavirus patient is considered protected, a phenomenon known as ‘natural immunity.’ At the first stage, individuals deemed to be recovered patients will not be vaccinated.” Other exclusions include people with a history of severe allergic reactions and children under 16.

A study from researchers at the Maccabi Institute for Research & Innovation, Maccabi Healthcare Services, and Sackler Faculty of Medicine, Tel Aviv University, has analysed the data of more than 500 000 people, of whom just over 350,000 had 13-24 days of follow-up post first vaccine dose, to estimate the efficacy of the Pfizer BioNTech vaccine. It found that the cumulative incidence of SARS-CoV-2 infection was 0.57% during days one to 12 and 0.27% in days 13-24. It concluded that a single dose of the vaccine was 51% effective 13-24 days post vaccination.

Meanwhile, researchers from the University of East Anglia reanalysed the same data and said that efficacy was “pretty much zero at day 14, but then rose to about 90% at day 21 before levelling off.” The team, who published a preprint on the findings, said that there was an initial surge in infection risk after having the vaccine, and suggested this could be because “people were less cautious about maintaining protective behaviours as soon as they have the injection.”

They added, “What our analysis shows is that a single dose of vaccine is highly protective, although it can take up to 21 days to achieve this. The early results coming from Israel support the UK policy of extending the gap between doses by showing that a single dose can give a high level of protection.”

 

Study details (1)
The effectiveness of the first dose of BNT162b2 vaccine in reducing SARS-CoV-2 infection 13-24 days after immunization: real-world evidence

Gabriel Chodick, Lilac Tene, Tal Patalon, Sivan Gazit, Amir Ben Tov, Dani Cohen, Khitam Muhsen
Maccabi Institute for Research & Innovation, Maccabi Healthcare Services, Sackler Faculty of Medicine, Tel Aviv University,

Published in medRxiv on 27 January 2021

Abstract
Background
BNT162b2 vaccines showed high efficacy against COVID-19 in a randomised controlled phase-III trial. A vaccine effectiveness evaluation in real life settings is urgently needed, especially given the global disease surge. Hence, we assessed the short-term effectiveness of the first dose of BNT162b2-vaccine against SARS-CoV-2 infection. Given the BNT162b2 Phase-III results, we hypothesized that the cumulative incidence of SARS-CoV-2 infection among vaccinees will decline after 12 days following immunization compared to the incidence during the preceding days.
Methods
We conducted a retrospective cohort study using data from 2·6 million-member state-mandated health provider in Israel. Study population consisted of all members aged 16 or above years who were vaccinated with BNT162b2-vaccine between December/19/2020 and January/15/2021. We collected information regarding medical history and positive SARS-CoV-2 polymerase chain reaction test from days after first dose to January/17/2021. Daily and cumulative infection rates in days 13-24 were compared to days 1-12 after first dose using Kaplan-Meier survival analysis and generalized linear models.
Findings
Data of 503,875 individuals (mean age 59·7 years SD=14·7, 47·8% males) were analysed, of whom 351,897 had 13-24 days of follow-up. The cumulative incidence of SARS-CoV-2 infection was 0·57% (n=2484) during days 1-12 and 0·27% (n=614) in days 13-24. A 51·4% relative risk reduction (RRR) was calculated in weighted-average daily incidence of SARS-CoV-2 infection from 43·41-per-100,000(SE=12·07) in days 1-12 to 21·08-per-100,000(SE=6·16) in days 13-24 following immunization. The decrement in incidence was evident from day 18 after first dose. Similar RRRs were calculated in individuals aged 60 or above (44.5%), younger individuals (50.2%), females (50.0%) and males (52.1%). Findings were similar in sub-populations and patients with various comorbidities.
Conclusions
We demonstrated an effectiveness of 51% of BNT162b2 vaccine against SARS-CoV-2 infection 13-24 days after immunization with the first dose. Immunization with the second dose should be continued to attain the anticipated protection.

 

Study details (2)
Estimating the effectiveness of the Pfizer COVID-19 BNT162b2 vaccine after a single dose. A re-analysis of a study of ‘real-world’ vaccination outcomes from Israel

Paul R Hunter, Julii Brainard

Published in medRxiv on 1 February 2021

Abstract
A distinctive feature of the roll out of vaccination against SARS-CoV-2 virus in the UK was the decision to delay the timing of the second injection till 12 weeks after the first. The logic behind this is to protect more people sooner and so reduce the total number of severe infections, hospitalisations, and deaths. This decision caused criticism from some quarters due in part to a belief that a single injection may not give adequate immunity. A recent paper based on Israel’s experience of vaccination suggested that a single dose may not provide adequate protection. Here we extract the primary data from the Israeli paper and then estimate the incidence per day for each day after the first injection and also estimate vaccine effectiveness for each day from day 13 to day 24. We used a pooled estimate of the daily incidence rate during days 1 to 12 as the counterfactual estimate of incidence without disease and estimated confidence intervals using Monte Carlo modelling. After initial injection case numbers increased to day 8 before declining to low levels by day 21. Estimated vaccine effectiveness was pretty much 0 at day 14 but then rose to about 90% at day 21 before levelling off. The cause of the initial surge in infection risk is unknown but may be related to people being less cautious about maintaining protective behaviours as soon as they have the injection. What our analysis shows is that a single dose of vaccine is highly protective, although it can take up to 21 days to achieve this. The early results coming from Israel support the UK policy of extending the gap between doses by showing that a single dose can give a high level of protection.

 

Adding to this analysis is a study by Professor Dvir Aran, a biologist at the Technion-Israel Institute of Technology, who suggests the vaccine is between 66%-85% effective at preventing infection and 87%-96% effective for preventing severe disease. The Daily Telegraph reports that the results are not quite as strong as Pfizer’s own phase three trial results but not far off.

“Our sensitivity analysis provides an estimate for the effectiveness of the vaccine in reducing positive and severe cases”, said the authors. “While this estimate is lower than the efficacy of the (Pfizer trial) it is still substantive and provides reassurance for the vaccine efficacy”.

The degree to which the Pfizer vaccine appears to block infection is the perhaps the strongest signal yet that it may block transmission of the virus – the key to eventually reaching herd immunity.

However, the results also suggest the first dose of the vaccine may not be “very effective” in reducing cases. This raises a possible concern over the UK strategy of leaving 12 weeks between shots, rather than the three weeks recommended by Pfizer.

“We see that immediately after the second dose the effectiveness jumps”, said Aran, adding that this could be explained by either the immediate impact of the second dose or the first dose coincidentally becoming effective on the three-week mark. “We will have to wait and see numbers from the UK”, he said.

The Daily Telegraph reports that another Israeli study shows the vaccination campaign appears to have had a marked impact on case numbers, hospitalisations and serious illness among those over 60 – the first group to be vaccinated.

Among this group, there was a 35% drop in cases, a 30% in hospitalisations and a 20% fall in those critically ill over the two weeks to February 1 (see charts below).

The study’s lead author Professor Eran Segal, a computer scientist at the Weizmann Institute, said: “We say with caution, the magic has started”. Segal said that by comparing their results with other age groups and the trends seen in the first wave of the pandemic, they could be “reasonably certain” that the vaccine was working.

 

[link url="https://www.bmj.com/content/372/bmj.n338"]BMJ material[/link]

 

[link url="https://govextra.gov.il/ministry-of-health/covid19-vaccine/en-covid19-vaccine-faqs"]Israeli Ministry of Health site[/link]

 

[link url="https://www.medrxiv.org/content/10.1101/2021.01.27.21250612v1"]medRxiv study (Open access)[/link]

 

[link url="https://www.medrxiv.org/content/10.1101/2021.02.01.21250957v1"]medRxiv study (Restricted access)[/link]

 

[link url="https://www.telegraph.co.uk/global-health/science-and-disease/magic-has-started-early-data-show-israels-vaccination-campaign/?"]Full report in The Daily Telegraph (Restricted access)[/link]

 

[link url="https://github.com/dviraran/covid_analyses/blob/master/Aran_letter.pdf"]GitHub study (Open access)[/link]

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