This week the world passed a major milestone in the global rollout of vaccines against COVID-19.
On Tuesday it was six months since the first vaccination was administered, outside a clinical trial, to 90-year-old Margaret Keenan at Coventry Hospital in the United Kingdom.
The anniversary has in large part passed without fanfare, with the Covid pandemic providing little time to look in the rear-view mirror.
In the six months since the world started vaccinating against COVID-19, more things about the vaccine have moved from the "unknown" category to the "known" category, including the impact of vaccination on hospitalisation and death.
What impact is vaccination having?
The impact of vaccination in countries that have managed to immunise a high proportion of their populations has been immense, including in reducing the number of people getting severely ill and hospitalised, and reducing the number of people dying.
In 2020 the United Kingdom was seen as one of the worst countries when it came to responding to the pandemic, but 2021 is a different story, with the country close to the top of the charts when it comes to vaccinating as many people as possible. Soon it will open up vaccination to people under the age of 30.
According to a study published in the journal Nature this week vaccination against COVID-19 in the United Kingdom reduced the number of new infections overall, "with the largest benefit received after two vaccinations and against symptomatic and high viral burden infections".
The study of more than 380,000 participants also found no evidence of any difference between the Pfizer and AstraZeneca vaccines in terms of results.
Professor Kristine McCartney, director of the National Centre for Immunisation Research and Surveillance said there are now 26 different studies into the impact of vaccination in countries like the United Kingdom, Israel and the United States.
"We're getting an array of very comprehensive studies now coming from those settings, looking at prevention of death, serious illness, hospitalisation, illness with any symptoms," Professor McCartney said.
Small countries like Bahrain and Bhutan were also among the most successful countries for the vaccine rollout, she said.
"If you're vaccinated, it's very clear that you're much less likely to become seriously ill or very few people become seriously ill if they're vaccinated," Professor McCartney said.
What about variants?
There are also studies showing the vaccines are working against different variants of COVID-19, but there is still more research to go in this area.
"Overall the vaccines have held up really quite well against the variants," Professor McCartney said.
"It differs a little bit between variant and between vaccines. But encouragingly, there are also now new strategies of how to approach the variants with vaccination."
Those new approaches include "tweaks" to mRNA vaccines like Pfizer and Moderna to change the "message" they send to the body to recognise and act on different variants.
Do we have data on whether the vaccines are stopping people transmitting the virus?
When the vaccines were first introduced, medical experts and health authorities told us it was too early to tell if getting the jab would stop a vaccinated person from transmitting the jab. Six months on and Professor McCartney believes we are closer to getting answers.
There have been two studies in the United Kingdom and one in Norway looking at the effect of vaccination on transmission of the virus in households, looking at the Pfizer and AstraZeneca vaccines in the UK, and Pfizer and Moderna in Norway.
Those studies are showing a 30 to 50 per cent reduction in the transmission to people in the same household or close community.
"Even if you were to be infected, your chances in passing it on to someone else would be cut in half," Professor McCartney said.
What does this mean for the next six months and beyond?
Since vaccination started around the world, more than 2 billion vaccines doses have been delivered. In a worldwide population of almost 8 billion people where many vaccines need two doses, there is still a long way to go.
According to Professor McCartney, the number of doses is something to be celebrated, but health authorities must next look to the question of how long the vaccines provide protection for, and what boosters may be needed.
"In Australia, we have to lay down that first layer of protection and then it's quite likely that we'll need to boost that protection in some, if not a number, of members of the community. But that will be something that comes more in the second phase," she said.