A recent study from Public Health England (PHE) yet to be peer-reviewed says that COVID-19 vaccine can kill transmission of the coronavirus by half, and one in four people show mild, short-lived side effects after having the AstraZeneca or Pfizer vaccines.
The study analyzed people who already had a single dose of either the Pfizer or AstraZeneca vaccines.
Those who were infected with the virus at least three weeks later were between 38% and 49% less likely to pass the virus on to people living in the same household, compared with those who had not been vaccinated.
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The protection was seen from around two weeks after vaccination and did not seem to differ with age, although most of those in the study were under 60.
Dr Peter English, a retired consultant in communicable disease control, said the study’s authors may even have underestimated the effect of vaccines on transmission.
He added:
The study has yet to be peer-reviewed and included over 57,000 people living in 24,000 households who were the contacts of a vaccinated person.
They were compared with nearly one million contacts of people who had not been vaccinated.
Another study has shown that one in four people have mild, short-lived side effects after receiving the Pfizer or AstraZeneca vaccines.
The most common side effects were headache, fatigue and tenderness, most peaking within 24 hours after vaccination and usually lasting one to two days.
The study is published in the Lancet Infectious Diseases and is based on analysis by researchers at King’s College London with data from the Zoe COVID Symptom Study app.
Tim Spector, professor of genetic epidemiology at King’s College London and lead scientist on the symptom study app, said:
The data comes from 627,383 users of the app who reported effects within eight days of receiving one or two doses of the Pfizer vaccine or one dose of the AstraZeneca vaccine between 8 December and 10 March.
Around 13.5% reported side-effects after their first Pfizer dose, 22% after the second Pfizer dose and 33.7% after the first AstraZeneca dose.
The most reported systemic side-effect was headache, with 7.8% of people reported suffering from headaches after the first Pfizer dose and 13.2% after the second Pfizer dose.
The research found more side-effects in those under the age of 55, and among women.
Participants who had previously had coronavirus were three times more likely to have side-effects affecting the whole body after receiving doses of the Pfizer vaccine than those without known infection.
They were almost twice as likely after the first dose of the AstraZeneca vaccine.