The US government’s first look at the real-world use of Covid-19 vaccines found their effectiveness was nearly as robust as it was in controlled studies.
The two vaccines available since December – Pfizer-BioNTech and Moderna – were 90 per cent effective after two doses, the Centres for Disease Control and Prevention (CDC) reported on Monday.
In testing, the vaccines were about 95 per cent effective in preventing Covid-19.
“This is very reassuring news,” said Mark Thompson, the study’s lead author. “We have a vaccine that’s working very well.”
The study is the government’s first assessment of how the shots have been working beyond the drug makers’ initial experiments. Results can sometimes change when vaccines are used in larger, more diverse populations outside studies.
With about 4,000 participants from six states, the study focused on healthcare workers, first responders and other front-line workers who had first priority for the shots. They were given nasal swab test kits to use every week to check for signs of infection.
“The evidence base for (currently available) Covid-19 vaccines is already strong and continues to mount ever higher with studies like this one,” said David Holtgrave, dean of the University at Albany’s School of Public Health.
The study included roughly 2,500 volunteers who received two vaccine doses, about 500 who received one dose and about 1,000 who were not vaccinated.
The researchers counted 205 infections, with 161 of them in the unvaccinated group. Of the remaining 44, the CDC said 33 of them were in people apparently infected within two weeks of their last shot.
A person is considered fully vaccinated two weeks after their final dose of vaccine.
No one that took part in the study died and only two were admitted to hospital. Mr Thompson did not say whether the people who were admitted were vaccinated or not.
“These findings should offer hope to the millions of Americans receiving Covid-19 vaccines each day and to those who will have the opportunity to roll up their sleeves and get vaccinated in the weeks ahead,” said agency head Dr Rochelle Walensky in a statement. “The authorised vaccines are the key tool that will help bring an end to this devastating pandemic."
Different studies have tried to look at how the vaccines have performed, including work done in Israel and the UK, and a US study of Mayo Clinic patients.
Unlike the Mayo study, which focused on hospital admission and death, the CDC study looked for any infection – including infections that never resulted in symptoms, or were identified before people started feeling sick.
About two-thirds of the participants who were vaccinated received Pfizer shots, one-third received Moderna shots and five received the newest shot from Johnson & Johnson.