A single dose of Pfizer and BioNtech's COVID-19 vaccine cuts the number of asymptomatic infections and could significantly reduce the risk of transmission of the virus, results of a UK study found on Friday.
Researchers analysed results from thousands of COVID-19 tests carried out each week as part of hospital screenings of healthcare staff in Cambridge, eastern England.
"Our findings show a dramatic reduction in the rate of positive screening tests among asymptomatic healthcare workers after a single dose of the Pfizer-BioNTech vaccine," said Nick Jones, an infectious diseases specialist at Cambridge University Hospital, who co-led the study.
After separating the test results from unvaccinated and vaccinated staff, Jones' team found that 0.80 percent tests from unvaccinated healthcare workers were positive.
Frequently Asked Questions
A vaccine works by mimicking a natural infection. A vaccine not only induces immune response to protect people from any future COVID-19 infection, but also helps quickly build herd immunity to put an end to the pandemic. Herd immunity occurs when a sufficient percentage of a population becomes immune to a disease, making the spread of disease from person to person unlikely. The good news is that SARS-CoV-2 virus has been fairly stable, which increases the viability of a vaccine.
There are broadly four types of vaccine — one, a vaccine based on the whole virus (this could be either inactivated, or an attenuated [weakened] virus vaccine); two, a non-replicating viral vector vaccine that uses a benign virus as vector that carries the antigen of SARS-CoV; three, nucleic-acid vaccines that have genetic material like DNA and RNA of antigens like spike protein given to a person, helping human cells decode genetic material and produce the vaccine; and four, protein subunit vaccine wherein the recombinant proteins of SARS-COV-2 along with an adjuvant (booster) is given as a vaccine.
Vaccine development is a long, complex process. Unlike drugs that are given to people with a diseased, vaccines are given to healthy people and also vulnerable sections such as children, pregnant women and the elderly. So rigorous tests are compulsory. History says that the fastest time it took to develop a vaccine is five years, but it usually takes double or sometimes triple that time.
This compared with 0.37 percent of tests from staff less than 12 days post-vaccination - when the vaccine's protective effect is not yet fully established - and 0.20 percent of tests from staff at 12 days or more post-vaccination.
The study and its results have yet to be independently peer-reviewed by other scientists, but were published online as a preprint on Friday.
This suggests a four-fold decrease in the risk of asymptomatic COVID-19 infection amongst healthcare workers who have been vaccinated for more than 12 days, and 75 percent protection, said Mike Weekes, an infectious disease specialist at Cambridge University's department of medicine, who co-led the study.
The level of asymptomatic infection was also halved in those vaccinated for less than 12 days, he said.
Britain has been rolling out vaccinations with both the Pfizer COVID-19 shot and one from AstraZeneca since late December 2020.
"This is great news – the Pfizer vaccine not only provides protection against becoming ill from SARS-CoV-2, but also helps prevent infection, reducing the potential for the virus to be passed on to others," Weeks said. "But we have to remember that the vaccine doesn’t give complete protection for everyone."
Key real-world data published on Wednesday from Israel, which has conducted one of the world's fastest rollouts of Pfizer's COVID-19 vaccine, showed that two doses of the Pfizer shot cut symptomatic COVID-19 cases by 94 percent across all age groups, and severe illnesses by nearly as much.Follow our full coverage of the coronavirus pandemic here.