Is there a COVID vaccine yet?
There have been several potential coronavirus vaccines reporting promising results in trials, but none have been authorised for use in the US or Europe yet.
Russia announced in August that its Sputnik V vaccine had been approved for use, but the announcement was criticised as being "dangerously early" because it had not yet been tested on a large number of people.
In November, Pfizer and Moderna announced their vaccines had proved to be 90% and 94.5% effective, respectively.
The news was hailed as promising by experts even though several outstanding questions remain, notably whether the vaccines protect against transmitting infection and how long their protection lasts.
Michael Mina, a professor at the Harvard School of Public Health, said that it is possible that there is an early immune response to the vaccine that does not persist, for instance. He said that the body may be making antibodies that later die.
“We may be measuring the effects of an impressive front line army that spins up in response to the vaccine - but then we should be careful not to assume the same efficacy persists to hold that line after most of the troops disappear,” Mina tweeted.
But, he added, the vaccine results showed that the vaccines were targeting the right protein and many have said the high efficacy provided hope that the vaccines would work against the virus.
“The more [antibodies] you start with the longer they last,” said Dr Barry Bloom, the former dean of Harvard T.H. Chan School of Public Health, at a press conference on 16 November. Dr Bloom said that the more than 90% efficacy was "probably better than any expert’s expectations."
Though experts say that as trials continue, that efficacy is likely to go down as more COVID-19 cases are confirmed among participants.
"We must assume [that] these clinical trials have been developed under 'optimal' conditions, and the efficacy data may differ -and eventually be lower- when the vaccines will be applied in field conditions," Professor Jose Vazquez-Boland, Chair of Infectious Diseases at the University of Edinburgh's medical school, told Euronews.
When will the first COVID-19 vaccines arrive in Europe?
"If all goes well and of course this is pending authorisation by the European Medicines Agency once they submit to be authorised, we would expect that we could possibly have vaccines available, possibly [the] end of 2020, beginning 2021," said EU Commissioner for Health Stella Kyriakides last week.
Andrea Ammon, who heads up the European Centre for Disease Control, put forward a similar timescale. She told AFP that in an optimistic scenario there could be vaccines by the first quarter of 2021.
Healthcare workers and those in vulnerable groups will be vaccinated first but the details of how that distribution chain will work are still being worked out, Ammon told AFP.
"In the best-case scenario, [vaccine distribution] could even be as early as before the end of 2020 for some pilot sector of the population, e.g. some at-risk people or healthcare workers, with mass vaccination being likely to be progressively rolled out along 2021," said Professor Vazquez-Boland at the University of Edinburgh.
The World Health Organization's chief scientist Dr Soumya Swaminathan said on 16 November: “We are looking at at least the first half of next year as being a period of very very limited doses. Supplies are going to be limited. There are bilateral deals that companies have done. So many of the doses have already been booked by some countries."
Meanwhile, the European Medicines Agency is working to authorise vaccines quickly and has already started a "rolling review" of some vaccines, to speed up the authorisation process.
How long before a COVID vaccine stops the pandemic?
Achieving herd immunity - the point at which a large enough portion of the population is immune that infection spread is prevented - would depend in part on how effective the vaccine is and its distribution.
Its origins come from veterinary medicine, Dr Vazquez-Boland explained to Euronews. The "threshold necessary to effectively halt the spread varies from one infectious disease to another", he added.
It depends in part on how infectious the disease is and how effective the immune protection is.
“We have plenty of vaccines that are life-saving vaccines, measles is an example of that, a highly efficacious vaccine over 95% efficacy and yet we still have measles outbreaks,” Dr Kate O’Brien, the World Health Organisation's director of immunisation, said at a press conference on Monday.
“Getting to vaccine efficacy is like building a base camp at Everest but the climb to the peak is really about delivering vaccines,” Dr O’Brien added.
Dr Bloom, who is also a research professor at Harvard, says: “There will still be lots of people that are not vaccinated in the first six months or year and they have the capacity to transmit infection."
This means that people, even those who are vaccinated, will need to continue wearing masks and practising some forms of distancing to prevent high levels of virus in the community, he added.
“There’s no question the higher the effectiveness of the vaccine the smaller the number of people that have to receive the vaccine to get to [herd immunity],” added Dr Bloom at a Harvard School of Public Health press conference.
What are the main challenges for distributing the vaccine?
Many existing vaccine distribution chains are in place to immunise children and adolescents. But the COVID-19 vaccines will need to target adults, who are more at risk for serious disease, experts say.
The best bet would be to have multiple vaccine candidates because some vaccines will be better for certain circumstances than others.
Professor Robin Shattock at Imperial College London's Department of Infectious Disease told Euronews that "reaching everyone and ensuring they get two doses [and] catching those that for whatever reason miss doses, will be a major undertaking".
That means that for some low- and middle-income countries, a one-dose shot that provides immunity and doesn't require any boosters would be better so that they don't have to find people again to get second doses.
But the vaccine will also need to be distributed to many different populations in higher-income countries as well.
Less access to primary care could result "in reduced access to the vaccine in poorer areas due to lack of human resources to deliver the programme in these areas," a Royal Society report said on vaccine distribution in the UK for instance.
"The cornerstone is always the primary care networks. These will need to be suitably reinforced and prepared to both implement the vaccination strategy and the (phase 4) monitoring of the safety and efficacy," said Professor Vazquez-Boland, who points out that monitoring any adverse effects of these new vaccines will be important.
Distribution is also impacted by how the vaccines are stored.
One advantage of the Moderna vaccine candidate, for instance, experts say, is that it does not need to be stored at ultra-cold temperatures, and can be stored in a normal refrigerator for 30 days, making distribution easier.
"It will also be a huge challenge to manufacture and distribute vaccines globally with the ever-present risk of a black market in fake/counterfeit vaccines," adds Professor Shattock.
How much of a problem is vaccine scepticism?
Experts have said that changing people’s opinions about vaccines could be key to making sure that herd immunity is achieved.
“I am concerned about the anti-vaccine movements,” Dr Bloom said, stating that it’s a “powerful movement” and the tools we have to deal with misinformation are more “limited” than the tools we have to get a vaccine to work.
Heidi Larson at the London School of Hygiene & Tropical Medicine told a Euronews-moderated panel in September that there were important lessons to be learned from the Ebola epidemic.
She said that experts needed to have "empathy" for individuals who might be unsure about a vaccine and work on building confidence. "We can get in there and start communicating and engaging," she said.