The COVID-19 vaccine developed by Pfizer and BioNTech is effective at preventing symptomatic and severe disease in people with some chronic illnesses, like diabetes and heart disease, the biggest real-world study showed on Thursday.
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The analysis of almost 1.4 million people by Israel's largest healthcare provider will offer further hope for countries as they get shots into citizens' arms, particularly those considered vulnerable, and curb the pandemic that has killed more than 3.1 million people.
The vaccine was 80% effective against symptomatic infection for people with heart or chronic kidney diseases, 86% for people with type 2 diabetes, 75% for cerebrovascular disease, and 84% for people suffering from immunodeficiency, according to the Clalit Research Institute study.
For people who were vaccinated and were already suffering three or more chronic conditions or risk factors, such as heart disease, neurological disease, chronic kidney disease, chronic lung disease, smoking, pregnancy or obesity, the research shows it was 88% effective in preventing symptomatic infection.
It was more than 90% effective against severe disease for people with type 2 diabetes, heart or cerebrovascular disease and 100% for people suffering from immunodeficiency.
The data is the latest from Israel where a universal and digitized healthcare system and the speedy vaccination program have allowed researchers insights into the vaccine's potency. Clalit covers more than half of Israel's population.
The results were lower than the 96% overall vaccine effectiveness seven days or more after the second dose, found by the study and the 95% effectiveness found in clinical trials last year.
But researchers said they offered some optimism that the vaccine still offers protection against severe illness in people who become infected after they get their shots.
"Protection is mildly reduced among patients with several co-morbidities. These results are very encouraging, as they suggest that most COVID-19 cases will be prevented by vaccination even in the elderly and chronically ill," said Professor Ran Balicer, Clalit's chief innovation officer.
"People with chronic diseases, multiple chronic or severe chronic diseases, should get vaccinated because the vaccine is very effective in protecting them against the high rates of complications that are expected," Balicer said.
The research was also carried out by Harvard and the University of Michigan and published in the New England Journal of Medicine on Thursday.
The Clalit study compared about 700,000 people vaccinated between Dec. 20, 2020 and Feb. 14 against the same size group of unvaccinated people, matching age, gender and other characteristics.
The subgroup of the people with chronic diseases was about 130,000 people, Balicer said.
More than half of Israel's 9.3 million population has been fully inoculated since its vaccination drive began in late December. COVID-19 cases have dropped continuously since a mid-January peak as the economy has largely opened.
Until mid-April, Israel has documented 98% fewer coronavirus cases, 93% fewer critically ill and 87% fewer COVID-19 deaths, according to Prof. Eran Segal, data scientist at the Weizmann Institute of Science.
Balicer said that although Israel was not yet at "herd immunity," the sharp drop was "proof of the potential of mass vaccination to really take us out of harm's way and shows the light at the end of the tunnel".
The large sample size allowed researchers to look more closely at subgroups of people with specific chronic diseases which would not necessarily be examined in a vaccine clinical trial, the researchers said.
It also found the vaccine to be 92% effective in preventing symptomatic COVID-19 among people over the age of 70, 96% for overweight people and 93% for those suffering obesity and provided 90% protection for people suffering from hypertension.
Danny Altmann, an immunology professor at the Imperial College London, said the study was among the first real-world research to offer such granular data into vaccinated subgroups.
"Transitioning into real-world application, the effectiveness still looks terrific, but inevitably there are people who make poor vaccine responses," he said in an email to Reuters.
"We need to know who they are, why, and what can be done to rescue immunity. Next, we need to see the results from each of the big cohort studies for the various patient groups."
The U.S. Centers for Disease Control and Prevention (CDC) Director Rochelle Walensky said that of the 84 million people who have been fully vaccinated in the United States, fewer than 6,000 have got sick with COVID-19 more than two weeks after being fully dosed.
Of those, nearly 400 were hospitalized and around 75 died, according to CDC data. Some of the hospitalizations and deaths were not due to COVID-19 infections.
Pfizer's late-stage clinical trial included people with co-morbidities. The most frequently reported co-morbidities were obesity (35.1%), diabetes (with and without chronic complications, 8.4%) and pulmonary disease (7.8%), a spokesman said.
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