The Deputy Chief Medical Officer has said news about Covid-19 vaccines is promising, but cautioned that "we will have to overcome vaccine hesitancy".
It comes after pharmaceutical company Moderna said its experimental vaccine was 94.5% effective in preventing Covid-19, based on interim data from a late-stage clinical trial.
It is the second US company in a week to report results that far exceed expectations.
Together with Pfizer's vaccine, also shown to be more than 90% effective, and pending more safety data and regulatory review, the US could have two vaccines authorised for emergency use in December with as many as 60 million doses of vaccine available by the year's end.
Next year, the US government could have access to more than one billion doses just from the two vaccine makers, more than needed for the country's 330 million residents.
The vaccines, both built using new technology known as messenger RNA or mRNA, represent powerful new tools to fight a pandemic that has infected 54 million people worldwide and killed 1.3 million.
The news also comes at time when Covid-19 cases are soaring, hitting new records in the US and pushing some European countries back into lockdowns.
"We are going to have a vaccine that can stop Covid-19," Moderna President Stephen Hoge said in a telephone interview.
Speaking at a briefing at the Department of Health, Deputy CMO Dr Ronan Glynn said that people are justifiably asking questions about these vaccines.
He said it is very important that we wait for the data, saying health officials will communicate with people when they are confident that these vaccines are safe and effective and not before that.
Dr Glynn said it is probably the first time in history we have seen an anti-vaccine campaign being organised in advance of the development of a vaccine.
He said people can expect to be fed with disinformation and lies and the National Public Health Emergency Team's job is purely to present the facts and to make sure people get accurate information.
.@ronan_glynn : "Vaccines at best are preventative, there is no vaccine yet developed that will help anyone who gets sick ... it's too early for people to drop their guard" | https://t.co/LRWAdClo1A pic.twitter.com/bTn2jGlat3— RTÉ News (@rtenews) November 16, 2020
Moderna's interim analysis was based on 95 infections among trial participants who received either a placebo or the vaccine.
Of those, only five infections occurred in those who received the vaccine, which is administered in two shots 28 days apart.
A key advantage of Moderna's vaccine is that it does not need ultra-cold storage like Pfizer's, making it easier to distribute.
Moderna expects it to be stable at standard refrigerator temperatures of 2C to 8C for 30 days and it can be stored for up to six months at -20C.
Pfizer's vaccine must be shipped and stored at -70C, the sort of temperature typical of an Antarctic winter.
It can be stored for up to five days at standard refrigerator temperatures.
The data from Moderna's 30,000 participant-strong trial also showed the vaccine prevented cases of severe Covid-19, a question that still remains with the Pfizer vaccine.
Of the 95 cases in Moderna's trial, 11 were severe and all 11 occurred among volunteers who got the placebo.
The European Commission said that positive results announced by US biotech firm Moderna for its Covid-19 vaccine candidate were encouraging and said the bloc was working to sign more supply deals with vaccine makers.
"More encouraging news from #COVID19 vaccine trials w/@moderna," EU health commissioner Stella Kyriakides said on Twitter.
The EU has been in talks with Moderna for its experimental Covid-19 vaccine at least since July, an internal EU document seen by Reuters showed.
On 24 August the EU Commission, which conducts talks with vaccine makers on behalf of EU states, said exploratory talks with Moderna had been concluded with the aim of signing a contract for the supply of 80 million doses of its vaccine, with the option of buying another 80 million.
"Signing contract w/ @pfizer & @BioNTech_Group later this week, more to come soon," Ms Kyriakides said.
More encouraging news from #COVID19 vaccine trials w/@moderna_tx publishing successful results today.— Stella Kyriakides (@SKyriakidesEU) November 16, 2020
We are doing everything we can to secure safe & effective vaccines.
Signing contract w/ @pfizer & @BioNTech_Group later this week, more to come soon. pic.twitter.com/eFTrU7AOAJ
Last week the Commission reached a deal with Pfizer and BioNTech on the supply of their potential Covid-19 vaccine hours after the companies announced their positive results, EU officials said, adding that the timing was a coincidence.
The formal signing of that contract is expected later this week.
Moderna, part of the US government's Operation Warp Speed programme, expects to produce around 20 million doses of the vaccine for the US this year, millions of which the company has already made, and is ready to ship if it receives FDA authorisation.
"Assuming we get an emergency use authorisation, we'll be ready to ship through Warp Speed almost in hours," Mr Hoge said.
"So it could start being distributed instantly."
The European Centre for Disease Control's principal expert Dr Agorista Baka said national governments may have multiple vaccines available to them at the same time, but logistical issues will arise in deploying them, in particular in transporting vaccines in a frozen condition.
Speaking to RTÉ's News at One, Dr Baka said that news from Moderna is exciting and offers "light at the end of the tunnel" and a fantastic tool to combat the virus.
The Chair of the National Immunisation Advisory Committee said it seems we can be "very hopeful" that vaccines will be generally available towards the spring or summer of next year.
Speaking on the same programme, Professor Karina Butler said plans are being put in place by the Governmental Immunisation Strategy so that the vaccines can be distributed and administrated and offered to those who are most likely to benefit from them, those who are most at risk and those who will have the least chance of having any potential adverse reaction to it.
She said at face value the announcement from Moderna is a breakthrough and that it is a very exciting day.
The 95 cases of Covid-19 included several key groups who are at increased risk for severe disease, including 15 cases in adults aged 65 and older and 20 in participants from racially diverse groups.
Most side effects were mild to moderate. A significant proportion of volunteers, however, experienced more severe aches and pains after taking the second dose, including about 10% who had fatigue severe enough to interfere with daily activities while another 9% had severe body aches.
Most of these complaints were generally short-lived, the company said.
Moderna's data provides further validation of the promising but previously unproven mRNA platform, which turns the human body into a vaccine factory by coaxing cells to make certain virus proteins that the immune system sees as a threat and mounts a response against.
Moderna expects to have enough safety data required for US authorisation in the next week or so and the company expects to file for emergency use authorisation in the coming weeks.
The United States has the world's highest known number of Covid-19 cases and deaths with more than 11 million infections and nearly 250,000 deaths.
The Trump administration has primarily relied on development of vaccines and treatments as its response to the pandemic.
Moderna has received nearly $1 billion in research and development funding from the US government and has a $1.5 billion deal for 100 million doses.
The US government also has an option for another 400 million doses.
The company hopes to have between 500 million and 1 billion doses in 2021, split between its US and international manufacturing sites and dependent in part on demand.
The US government has said Covid-19 vaccines will be provided free to Americans, whether they have health insurance, are uninsured or are covered by government health programs such as Medicare.
Moderna also said it will use its data to seek authorisation in Europe and other regions.
Other countries such as China and Russia have already begun vaccinations.
Russia licensed its "Sputnik-V" Covid-19 vaccine for domestic use in August before it released data from large-scale trials.
It said on 11 November that its vaccine was 92% effective based on 20 infections in its large trial.
Vaccine will not be enough to stop pandemic, says WHO chief
The head of the World Health Organization has said that a vaccine would not by itself stop the coronavirus pandemic.
There have been more than 54 million cases of Covid-19 since it broke out in China last year and more than 1.3 million people have died.
"A vaccine will complement the other tools we have, not replace them," director-general Tedros Adhanom Ghebreyesus said. "A vaccine on its own will not end the pandemic."
The WHO's figures for Saturday showed that 660,905 coronavirus cases were reported to the UN health agency, setting a new high water mark.
That number, and the 645,410 registered on Friday, surpassed the previous daily record high of 614,013 recorded on 7 November.
Dr Tedros said that supplies of the vaccine would initially be restricted, with "health workers, older people and other at-risk populations (to) be prioritised.
"That will hopefully reduce the number of deaths and enable the health systems to cope."
But he warned: "That will still leave the virus with a lot of room to move. Surveillance will need to continue, people will still need to be tested, isolated and cared for, contacts will still need to be traced... and individuals will still need to be cared for."
There are currently more than three dozen other Covid-19 vaccine candidates in development, 11 of which are in or have completed phase 3 trials.