The chairman of Pfizer has said he is not yet sure whether their new vaccine will stop the spread of coronavirus.
In an interview for NBC's Dateline prime-time special titled “Race for a Vaccine”, Albert Bourla admitted he was 'not certain' it would stop Covid-19 from being transmitted.
The Pfizer/BioNTech Covid-19 vaccine has been declared safe for use and is one of the three leading candidates that have led the desperate global search for a way to end the pandemic.
The first batches are already enroute to Britain today, as the UK hopes for millions of doses by the end of the year.
Covid 19 Time Series
Pfizer last month declared its vaccine safe and announced that its candidate had been shown to be more than 90% effective at preventing Covid-19.
However, the vaccine, which is delivered in two doses, is one of the more challenging products to distribute.
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It must be stored in below-freezing temperatures to be transported around the world, while Oxford and AstraZeneca's shot requires a chilled, rather than frozen 'cold-chain.'
In a list of interview highlights released before Dateline's special, Mr Bourla was asked by interviewer Lester Holt whether Pfizer's jab will stop people passing on the vaccine to others.
He asks: “Even though I’ve had the protection, am I still able to transmit it to other people?”
Mr Bourla responds: “I think this is something that needs to be examined. We are not certain about that right now with what we know."
The chairman was explaining it was still uncertain whether people could continue to be carriers of the virus after receiving the vaccination.
Vaccines for infectious diseases most of the time will protect the host - but don't always completely stop the virus being carried and spread to other people.
For instance, the US Center for Disease Control (CDC) explains that the MMR vaccine prevents most, but not all, cases of mumps and complications caused by the disease.
People who receive two doses of the MMR jab are about nine times less likely to get mumps than unvaccinated people who have the same exposure to mumps virus, according to the CDC.
However, some people who receive two doses can still get mumps, especially if they have prolonged, close contact with someone infected.
But the CDC explains that a vaccinated person does get mumps, they will likely have less severe illness than an unvaccinated person.