Scientists said the data was further encouraging news.
Although the full trial data has yet to be published, the companies say there have been no serious safety concerns.
However, they did notice headaches and fatigue in about 2% of volunteers given the vaccine, although older people seemed to experience minimal side effects.
There is also evidence that the vaccine protects against severe Covid – but this is based on only 10 cases.
It’s still unclear how long protection from the vaccine lasts and if it stops people transmitting the virus.
In the trial, 42% of all participants are from diverse ethnic backgrounds and 41% are aged between 56 and 85 years old.
The trial, which is testing people at 150 sites in the US, Germany, Turkey, South Africa, Brazil and Argentina, will collect data on the safety and efficacy of the vaccine for another two years.
Pfizer and BioNTech expect to produce up to 50 million doses of the vaccine this year and up to 1.3 billion doses by the end of 2021.
There are hundreds of vaccines in development around the world, and about a dozen in the final stages of testing, known as phase three.
The first two to show any results – made by Pfizer-BioNTech and Moderna – both use an experimental approach, called mRNA, which involves injecting part of the virus’s genetic code into the body to train the immune system.
Antibodies and T-cells are then made by the body to fight the coronavirus.
Russia’s Sputnik vaccine has also released early data from phase three based on a smaller number of volunteers and Covid cases.
There are some logistical challenges with mRNA vaccines, namely the need to store them at cold temperatures.
The Pfizer vaccine must be stored at around minus 80C, although it can be kept in a fridge for five days.
Moderna’s vaccine needs to be stored at minus 20C for up to six months and kept in a standard fridge for up to a month.
The first report on the Russian coronavirus vaccine, named Sputnik-V, says early tests showed signs of an immune response.
The report published by medical journal The Lancet said every participant developed antibodies to fight the virus and had no serious side effects.
Russia licensed the vaccine for local use in August, the first country to do so and before data had been published.
However, experts say the trials were too small to prove effectiveness and safety.
But Moscow has hailed the results as an answer to critics. Some Western experts have raised concerns about the speed of Russia’s work, suggesting that researchers might be cutting corners.
Last month, President Vladimir Putin said the vaccine had passed all the required checks and that one of his own daughters had been given it.
Two trials were conducted between June and July, The Lancet paper said. Each involved 38 healthy volunteers who were given a dose of the vaccine and then a booster vaccine three weeks later.
The participants – aged between 18 and 60 – were monitored for 42 days and all of them developed antibodies within three weeks. Among the most common side effects were headaches and joint pain.
The trials were open label and not randomized, meaning there was no placebo and the volunteers were aware they were receiving the vaccine.
According to the report: “Large, long-term trials including a placebo comparison, and further monitoring are needed to establish the long-term safety and effectiveness of the vaccine for preventing Covid-19 infection.”
A third phase of trials will involve 40,000 volunteers from “different age and risk groups,” according to the paper.
Russia’s vaccine uses adapted strains of the adenovirus, a virus that usually causes the common cold, to trigger an immune response.
Kirill Dmitriev, head of a Russian investment fund behind the vaccine, said during a news conference that the report was “a powerful response to the skeptics who unreasonably criticized the Russian vaccine”.
He said that 3,000 people had already been recruited for the next phase of trials.
Health Minister Mikhail Murashko said Russia would start vaccinations from November or December, with a focus on high-risk groups.
However, experts warned that there was still a long way to go until a vaccine could enter the market.
According to the WHO, there are 176 potential vaccines currently being developed worldwide. Of those, 34 are currently being tested on people. Among those, eight are at stage three, the most advanced.
Mikhail Murashko, quoted by Interfax news agency, said that the Gamaleya Institute, a research facility in Moscow, had finished clinical trials of a vaccine and that paperwork was being prepared to register it.
“We plan wider vaccinations for October,” he said, adding that teachers and doctors would be the first to receive it.
Last month, Russian scientists said that early-stage trials of an adenovirus-based vaccine developed by the Gamaleya Institute had been completed and that the results were a success.
Last month the US, UK and Canada security services said a Russian hacking group had targeted various organizations involved in Covid-19 vaccine development, with the likely intention of stealing information.
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