A possible breakthrough vaccine for Covid-19 is likely to involve people getting more than one dose and it is still unclear how long its protection against the deadly virus would last, a leading scientist said yesterday.
Kingston Mills, professor of experimental immunology in Trinity College, was commenting after studies have sparked debate on how vaccines against the virus might work.
A global race is on to develop a vaccine and in an optimistic forecast Dr Anthony Fauci, of the US National Institute of Allergy and Infectious Diseases, said one could be ready at the end of the year.
Prof Mills said: "Several different approaches are being developed. If one of them works it would be great, and it would be unfortunate if none worked."
One of the studies which has led to debate on how long a vaccine might work involved 96 people who were tracked by a team at King's College in London.
It found 60pc had a strong antibody response at the height of their infection. This dropped to 17pc three months later and in some the antibodies were not detectable.
The question for researchers now is that if natural antibodies fall off, what impact will that have on how effective vaccines will be?
Prof Mills said it will not be possible to know how long a vaccine will last until data from clinical trials is available.
"All the early data is based on short-term testing after immunisation," he said. "You would not know for a year or two after using the vaccine how quickly the immune response drops off."
He said the likelihood is that people will need "at least two doses" of the vaccine.
Meanwhile, it emerged yesterday that Moderna will start the final stage of human trials for its vaccine candidate on July 27.
This follows promising results from earlier testing. The study should run until October 2022 but preliminary results should be available well before then.
The company aims to enrol 30,000 adults in the clinical trial, which is designed to test whether the vaccine works to prevent Covid-19.
The trial will also examine the vaccine's safety.
Those who take part in the trial will either receive the vaccine or a placebo.
They will be tracked for two years to see whether they get Covid-19 or have any negative reactions to the vaccine.
The researchers will also periodically measure participants' antibody levels.
Moderna has also published data from its phase one clinical trial in the 'New England Journal of Medicine'.
That trial, which involved 45 volunteers, was aimed at testing the new drug's safety, not its effectiveness.
But the company said results from all 45 participants showed they developed antibodies key to fighting the virus at levels up to four times the amount found in patients who got sick and then recovered from the virus.
Researchers point out that while the findings are promising, scientists have not yet shown that Covid-19 antibodies lead to immunity, and if so, how long it lasts.
Everyone involved in the trial receives two shots of the vaccine, 28 days apart.
The most common side effects were fatigue, chills, headache and weakness, the study found.
The company said it is committed to advancing the clinical development of the vaccine "as quickly and safely as possible while investing to scale up manufacturing so that we can help address this global health emergency".