The World Health Organization’s Health Emergencies Programme executive director Michael Ryan said on Wednesday that vaccines should not be seen as a “unicorn” solution, and are likely to arrive too late to play a role in the second-wave surge in infections being seen in Europe and the Americas.

“I think it’s at least four to six months before we have significant levels of vaccination going on anywhere,” he said, during a public question and answer session.

While it is difficult to pin down an exact number, scientists generally estimate that at least two-thirds of populations – or even as many as 90 per cent – would need to be vaccinated for a “herd immunity” phenomenon to kick in, where the level of people who cannot get infected in a community stops or significantly reduces the virus’ ability to spread.

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Gregory Gray, an infectious disease epidemiologist at Duke University in the US, said even as a vaccine roll-out could allow for some of our current Covid-19 control measures to be reduced, it was important to remain “cautious and vigilant for future outbreaks”, as distribution would not be universal right away.

“Sars-CoV-2 is likely to be around for a long time. While we will soon have vaccines available to many, we would need to protect the vast majority of the world’s population to knock down the Sars-CoV-2 prevalence to levels where we could altogether stop wearing masks and stop social-distancing efforts,” he said.

Getting enough doses out to the world will take time, coordination and infrastructure. Pfizer and BioNTech have said they could produce 1.3 billion doses by the end of 2021. Several hundred million doses are already booked by major economies like the US and EU.

Each immunisation requires two doses and there is an additional hurdle – they need to be transported and stored at minus 70 degrees Celsius (minus 94 Fahrenheit).

All told, leading vaccine makers have projected that some 16 billion doses could be made next year, according to data collected last month by British life sciences analytics firm Airfinity, but it remains to be seen if and when all these vaccines will come online and how distribution hurdles will be overcome.

Nevertheless, the announcement on Wednesday from Pfizer and BioNTech provides a new jolt of hope that there is an end in sight to a pandemic that has caused more than 1.3 million deaths worldwide.

“It’s an absolute landmark,” said Kylie Quinn, a vice-chancellor’s research fellow at RMIT University in Melbourne.

“It leverages so much information that we have been building over the past 20-25 years trying to make vaccines for other things, like HIV, TB, malaria, Ebola. All of this information has enabled us to respond with such speed, and it has such implications [for] future development of vaccines over the next 10 years,” she said.

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Pfizer and BioNTech announced results after their trial reached a planned end point of 170 infections of Covid-19 among their nearly 44,000 participants. Of the cases, 162 were observed in the placebo group, while there were eight cases among those who had received the vaccine candidate, BNT162b2.

The efficacy rate of 95 per cent was consistent across age, gender, race and ethnicity demographics, the companies said.

Notably, the observed efficacy for adults over 65 years of age was over 94 per cent, an important marker for a group whose Covid-19 mortality rate far exceeds younger age groups. Some vaccines, such as that for influenza, are not as effective in older adults because of their weakened immune systems.

But questions remain about the long-term efficacy of the vaccine and its ability to protect recipients from spreading Covid-19. Experts say that generally if people are not becoming sick, their ability to spread the disease is likely to be reduced because of the lower levels of the virus.

Immunologist Ashley St John, an associate professor at Duke-NUS Medical School in Singapore, said it was possible the efficacy of BNT162b2 could decline with time, but “there could be ways to make a good vaccine better, including through optimising the vaccination schedule”.

“Right now, Covid is spreading like a wildfire and we need a vaccine that can help us, even if for the short term, to get this under control,” she said. The trial will continue to collect efficacy and safety data from participants for an additional two years.

Both vaccines use a novel mRNA platform and a design targeting the virus’ spike protein.

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The fact that they are reporting similar results – not only on efficacy but also on indications that the vaccines may protect against severe disease – adds to the strength of the data sets, according to RMIT’s Quinn.

“We are starting to build the picture, and it seems that with both of these vaccines there is a good chance they are going to protect well against severe disease, which is huge,” she said.

Additional reporting by Zhuang Pinghui