At the end of a long, dark COVID-19 winter, vaccines are the spring we’ve all been waiting for. If you had asked most scientists this time last year whether they thought that we would have a COVID-19 vaccine licensed and given to millions of people by the start of 2021, the answer would almost certainly be “absolutely not”.
And yet, here we are. Millions of people already immunized, safe from the numerous harms of COVID-19. It’s been a doom-filled year, but things are really looking up for us all.
How good are the vaccines really? Well, we already knew, from the massive clinical trial evidence, that our COVID-19 vaccines were safe and effective enough to use — even a relatively bad vaccine is much safer than infection with COVID-19. But now we have real-world data rolling in from tens of millions of vaccinations, which allows us to see things at a population scale.
The results are in. And they are looking good.
So here are some facts about COVID-19 vaccinations to brighten your day.
They Are Safe
As I’ve written before, we knew from clinical trial evidence that there were no common serious adverse events from COVID-19 vaccines. Given the size of the trials, we could exclude things that happened once every few thousand people, which means that any serious issues had to be pretty rare.
But, with millions vaccinated, we can put a number on just how often these serious side-effects — things that can be life-threatening — happen.
In a word? Rarely.
Using data from the UK and US, we can confidently say that the rate of serious issues associated with vaccination is somewhere around 10–15 per million vaccine doses given. The most common serious problem is anaphylaxis, which makes up the vast majority of the reported vaccine serious adverse events. There are a few other worries, which vary from vaccine to vaccine — for example, the UK regulator is monitoring whether Bell’s Palsy may be a very rare side-effect — but anaphylaxis is definitely the most common serious reaction.
And between these two countries, with a combined ~80 million vaccine doses given, there have so far been 0 deaths associated with COVID-19 vaccination. Given an infection fatality rate of 0.5–1% (roughly), that makes vaccines at least 400,000x safer than getting COVID-19. Probably more.
They Are Effective
Yes, we knew that COVID-19 vaccines were efficacious before — we knew that, in clinical trials, they prevented a large proportion of COVID-19 cases.
But what happens when you start giving these vaccines in the real world?
With data from real people who have been vaccinated, we now know that the exact same thing happens. People who have been vaccinated are substantially less likely to contract COVID-19. One large study of 100,000s of people in Israel found that a single dose of the Pfizer/BioNTech vaccine prevented 46% of COVID-19, and both doses pushed this up to 92%. That’s people in the real world who got their vaccines on schedule. Another study in Britain found similar levels of effectiveness for the Astrazeneca vaccine, despite its slightly lackluster performance in clinical trials.
Overall, the vaccines appear to live up to the hype. Not only do they prevent an enormous amount of disease, they also appear to prevent the worst complications of COVID-19 as well — in the Israeli study, people with two doses of the vaccine were >90% less likely to go to hospital or die from COVID-19 compared to those who had not been vaccinated. While this evidence is observational, and thus imperfect, it matches up with clinical trial data almost exactly. It is almost certain that this represents a true reduction in severe issues caused by the coronavirus that happens after you get your vaccine.
They Prevent Transmission As Well As Disease
Last but not least, we have the least certain but perhaps most exciting fact — vaccines appear to prevent not just symptomatic COVID-19, but transmission as well. That means that, once you’re vaccinated, not only will you be far less likely to get sick from coronavirus yourself, you will be unlikely to spread the disease to others as well.
This is, in a word, fantastic. It is also, however, a bit uncertain still.
We know from preclinical studies and evidence from people who have been vaccinated that it’s very likely that people who are immunized will spread the disease much less. Unfortunately, even with this evidence it’s hard to be definite about whether vaccines prevent transmission entirely, a little bit, or a lot.
That doesn’t mean that we have no information. We know that the vaccines currently in use probably do prevent transmission. A recent modelling paper suggested that the Pfizer vaccine was at least 61% protective against transmission after a single dose, and potentially up to 90% effective after two. An informal analysis on Twitter from infectious disease ecology expert Professor Kilpatrick showed a similar reduction associated with the Moderna vaccine.
While these transmission benefits are likely to vary from vaccine to vaccine, and may not be quite as large as our initial models suggest, they are still amazingly good news. It looks like vaccines really can halt the pandemic in its tracks.
The main message here is pretty simple — get vaccinated when your turn comes. The vaccines are safe, effective, and given they prevent transmission will save not just your own life but the lives of the people around you.
Yes, it’s normal to be a tad worried about vaccines. I absolutely understand being a bit nervous, because before I studied them I was quite afraid of needles myself. Some people like to shame and ridicule those who are concerned about vaccination, but given that I was once that person I think it’s worth being empathetic. If you’ve ever got a serious concern about vaccines, I try to respond to every question asked on twitter.
But the data is in. The checks have been done. COVID-19 vaccines are saving the world, one slightly sore arm at a time.