Study reveals single vaccine dose can reduce household transmission of COVID-19 by up to half

London [UK], April 29 : A single dose of the COVID-19 vaccine can limit household transmission by up to half, according to a study by Public Health England released on Wednesday, signalling the effectiveness of the vaccines at preventing spread.
According to The Hill, the research -- which has yet to be peer-reviewed -- found that people who got COVID-19 three weeks after receiving one dose of either the Pfizer-BioNTech or AstraZeneca vaccines were between 38 per cent and 49 per cent less likely to give the virus to those in their household, compared to those who didn't receive any vaccine dose.
Public Health England analyzed more than 57,000 contacts from 24,000 households in which a person who had received a vaccine dose tested positive for the virus and compared it with almost 1 million contacts of cases among unvaccinated people.
"We have shown that both the vaccines are associated with reduced likelihood of household transmission by 40-50 per cent from individuals diagnosed with COVID-19 after vaccination, highlighting important wider benefits to close contacts," the conclusion of the research read.
"These results could also have implications for transmissibility in other settings with similar transmission risks. These would need to be considered in future pandemic modelling to fully capture the impact of the vaccination programme and to inform public health strategies and public communication going forward," it added.
The Hill reported that cases among household contacts were considered secondary cases if they received a positive COVID-19 test two to 14 days after the initial case.
The researchers found protection was present about 14 days after vaccination and remained steady despite the different ages of cases or contact. The measured protection is in addition to the 60 per cent to 65 per cent decreased risk of the vaccinated person developing symptomatic COVID-19 four weeks after one dose.
Researchers said the results would likely be similar in other high-risk transmission locations besides households, such as shared accommodations and prisons.
British Health Secretary Matt Hancock called the study "terrific news," saying, "We already know vaccines save lives and this study is the most comprehensive real-world data showing they also cut transmission of this deadly virus."
"It further reinforces that vaccines are the best way out of this pandemic as they protect you and they may prevent you from unknowingly infecting someone in your household," he added in a statement, as quoted by The Hill.
But Mary Ramsay, head of immunization at Public Health England, still encouraged caution, saying "even if you have been vaccinated, it is really important that you continue to act like you have the virus, practise good hand hygiene and follow social distancing guidance."
Vaccine recipients are still able to test positive for COVID-19, even after being fully vaccinated, because vaccines are not 100 per cent effective. But the vaccines have been found to decrease the risk of severe illness and death from COVID-19.
Meanwhile, The Pfizer and Moderna vaccines were 94 per cent effective in preventing hospitalization for COVID-19 among people age 65 and older, according to a US Centers for Disease Control and Prevention (CDC) study released Wednesday.
The study provides new evidence on the benefits of vaccination and builds on results from the clinical trials by adding real-world evidence from 417 hospitalized adults in 14 states from January to March.
"This multisite U.S. evaluation under real-world conditions suggests that vaccination provided protection against COVID-19-associated hospitalization among adults aged [65 and older]," the study states.
In the US, as more people are vaccinated, deaths from COVID-19 have fallen markedly, from highs in January of more than 3,000 per day to about 650 per day currently, according to CDC data.