First dose of vaccine already cuts covid transmission

londonA single dose of covid vaccine can stop transmission of the virus by almost 50%. The data comes from a study, yet to be reviewed, made public on Wednesday morning by Public Health England (PHE).

Thus, people who have received a first dose of the Pfizer or AstraZeneca vaccines, and who nevertheless became infected three weeks later - when it is considered that the human body has developed sufficient antibodies - are between 49 and 38% less likely to transmit the virus than unvaccinated people.

The study included more than 57,000 contacts from 24,000 different households in which there had been a PCR-confirmed case, compared with almost one million contacts of unvaccinated people. When the detected case of infection had not received any type of vaccination, 10% of the people in their household bubble were infected. Contacts were defined as secondary covid cases if they tested positive two to 14 days after the initial household case. Most of the people in the study were under 60 years of age.

The PHE study has also shown that protection against covid manifests around 14 days after vaccination, with similar levels of immunity regardless of age of the cases or contacts.

Mary Ramsay, head of vaccination at PHE, said in a statement: "Not only do vaccines reduce the severity of the disease and prevent hundreds of deaths every day, but we now see that they also have an additional impact by reducing the likelihood of transmitting covid to others."

In terms of households being high-risk spaces for transmission, the findings advance evidence on the potential reach of the vaccination campaign in preventing onward transmission. Therefore, "similar results could be expected in other settings" with similar transmission risks.