The Pfizer-BioNTech mRNA vaccine was shown to be 95% effective in preventing severe COVID-19 infection in clinical trials. However, given that the acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to spread and evolve into several concerning variants, it remained unknown how the vaccine would respond in a real-life setting.
With the number of global cases rising to over 114 million, Israel has reported 775,807 cases and 5,752 deaths.
Israel has become a unique case study to observe vaccine effectiveness. Compared to most countries, Israel has been proactive in vaccinating almost all of the population.
New research led by Ran D. Balicer from the Clalit Research Institute in Boston suggests that the data provide strong evidence that the Pfizer-BioNTech vaccine works to prevent hospitalization and severe COVID-19 infection.
The authors write:
“This study estimates a high effectiveness of the BNT162b2 vaccine for preventing symptomatic Covid-19 in a noncontrolled setting, similar to the vaccine efficacy reported in the randomized trial. Our study also suggests that effectiveness is high for the more serious outcomes: hospitalization, severe illness, and death.”
The study “BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Mass Vaccination Setting” was published in The New England Journal of Medicine.
Between December 20, 2020, to February 1, 2021, the researchers analyzed data from Clalit Health Services, which covers about 53% of Israel’s population. They investigated outcomes in 596,618 people who were newly vaccinated.
“The five outcomes of interest were documented SARS-CoV-2 infection confirmed by positive PCR test, documented symptomatic Covid-19, hospital admission for Covid-19, severe Covid-19 (according to National Institutes of Health criteria) and death from Covid-19,” write the research team.
Outcomes after the first dose
About 15 days after the first dose, there were 10,561 reported infections. Of these, 5,996 (57%) showed symptoms of COVID-19 disease, 369 were admitted to the hospital, 229 were reported with severe COVID-19 infection, and 41 died.
The researchers also found that 14 to 20 days after the first dose, the vaccine was 46% effective with documented infection, 57% with symptomatic COVID-19 infection, 74% with hospitalization, 62% in preventing severe illness, and 72% in preventing death.
The estimated effectiveness for the vaccine increased to 60% 21 to 27 days after the first injection. The results showed a 66% effectiveness with symptomatic infection, 78% with hospitalization, 80% in preventing severe illness, and 84% in preventing death.
Vaccine benefits increase over time
After a 21-day follow-up, the researchers found that 96% of people had received their second Pfizer-BioNTech vaccine.
The vaccine’s effectiveness rose 7 days after the second dose. They observed it was 92% effective for documented infections, 94% for symptomatic infections, 87% for hospitalization, and 92% effective in preventing severe infection.
Low effectiveness observed for asymptomatic cases
A separate analysis with asymptomatic cases found the vaccine was 29% effective 14 to 20 days after the first dose and 52% effective 21 to 27 days after the first dose.
The vaccine was 90% effective 7 or more days after people received the second dose.
Pfizer-BioNTech vaccine outcomes in vulnerable populations
Given the large population sample, the researcher was able to look at vaccine effectiveness in various age groups. For people 70 years or older and younger age groups, they found it similar to the 94% to 96% efficacy observed in clinical trials.
People with multiple preexisting conditions showed lower vaccine effectiveness than healthy people.
Estimated effectiveness toward the B.1.1.7 variant
The Pfizer-BioNTech vaccine did not test against any of the current variants spreading worldwide. However, in this study, approximately 80% of the sequenced SARS-CoV-2 virus were of the B.1.1.7 variant. The B.1351 variant was reported to be very rare in Israel to perform any substantial data analysis.
The researchers warn that their limited dataset makes them unable to provide a specific estimate for the B.1.1.7 variant. However, based on the limited dataset, they suggest the vaccine could be potentially useful against the B.1.1.7 variant as they observed neutralizing antibodies present after vaccination.
“These results strengthen the expectation that newly approved vaccines can help to mitigate the profound global effects of the Covid-19 pandemic.”