Which COVID-19 Vaccine Is Best? Why Comparing Vaccines Is Harder Than It Looks
Please note: this article was written in mid-2021, early in the COVID-19 vaccine rollout. Vaccines, boosters and recommendations have changed a lot since then. For current advice, ask your doctor or check your national health authority, for example the Australian Department of Health.
There is no single “best” COVID-19 vaccine. Trial results can't be compared fairly, and real-world data showed the main vaccines all protected strongly against severe illness. The best vaccine is the one recommended for you and available to you now.
As COVID-19 vaccines rolled out around the world, one question came up again and again: which vaccine is the best one? It's a fair thing to ask. But the answer is less simple than it sounds, and it starts with what we actually mean by "best".
What Does “Best” Even Mean for a COVID-19 Vaccine?
"Best" can mean very different things depending on what matters most to you:
Keeps you out of hospital and protects you from the worst outcomes.
Protects against the virus variants circulating where you live.
Gives protection that lasts longer before another dose is needed.
Has the best balance of benefits and risks for people like you.
Even if we could agree on one definition, most people didn't get to choose their vaccine in 2021. Supplies were limited, so people received whichever vaccine was available. That choice was guided by clinical data, health authority recommendations and, for people with medical conditions, their doctor's advice.
Why Is It So Hard to Compare COVID-19 Vaccines?
Clinical trial results only go so far
You might expect clinical trials to settle the question. Large phase 3 trials, usually involving tens of thousands of people, are the basis for approval by regulators around the world. They compare the number of COVID-19 cases in people who got the vaccine with those who got a placebo. That gives the vaccine's efficacy: how well it works under the tightly controlled conditions of a trial.
The trials did show different results:
| Vaccine | Efficacy against symptomatic COVID-19 (phase 3 trials) | Source |
|---|---|---|
| Pfizer-BioNTech | About 95% | NEJM, 2020 |
| AstraZeneca (Oxford) | 62% to 90%, depending on the dosing schedule | The Lancet, 2020 |
Why those numbers aren't directly comparable
Each phase 3 trial was run in a different place and at a different time. That means:
- Infection levels in the community were different.
- Public health measures such as lockdowns and masks varied.
- Different virus variants were circulating.
- Volunteers differed in age, ethnicity and underlying health conditions.
So putting the headline efficacy figures side by side can be misleading. During a pandemic, when vaccines are in short supply, it can even be harmful, if it makes people wait for a "better" vaccine instead of taking the one they're offered.
How Can Vaccines Be Compared Fairly?
The fairest way is a head-to-head trial. This is a single study that compares two vaccines directly, in the same population, at the same time, using the same measurements. Because every other factor is the same, any difference in the results comes down to the vaccines themselves.
For example, a phase 3 trial in the UK compared the Valneva vaccine with AstraZeneca. It was still running in mid-2021 and reported its results in October 2021.
What Does Real-World Data Show?
While head-to-head trials take time, we can learn a lot from how vaccines perform in the general population. Real-world data tells us about a vaccine's effectiveness, as opposed to its efficacy in a trial.
How well a vaccine works in a controlled clinical trial.
How well it works in everyday life, across the whole population.
Effectiveness is easiest to compare in countries that used more than one vaccine in the same population. In the UK, Public Health England data from 2021 showed that Pfizer and AstraZeneca performed similarly well. Both reliably protected against symptomatic COVID-19, hospitalisation and death, even after a single dose.
So a vaccine that looked "best" on trial efficacy alone didn't necessarily come out ahead in the real world.
What About the Future?
The first COVID-19 vaccine you get is unlikely to be your last. Immunity naturally fades over time, so booster doses are needed to keep protection strong.
- Mixing vaccines: data from Spain's CombiVacS trial showed that giving a different vaccine for a later dose was safe and triggered a strong immune response. That made "mix and match" a useful strategy for keeping protection high.
- Variants: new variants were already circulating in 2021. Existing vaccines gave somewhat less protection against them but still protected people well.
- Updated vaccines: companies including Moderna were already working on variant-specific boosters. Updated vaccines did later become part of booster programs.
In other words, the "best" vaccine may turn out to be a combination of different vaccines over time. A vaccine with the highest efficacy in a phase 3 trial won't necessarily be the one that best protects you against the variants circulating in the future.
The Bottom Line
Wanting the "best" vaccine is completely understandable. But the best vaccine for you is the one available to you now, because it:
- reduces your chance of catching COVID-19,
- cuts the spread to vulnerable people in your community, and
- greatly lowers your risk of serious illness.
All the approved vaccines did this, and did it well. Those benefits grow as more people are vaccinated, building community protection (often called herd immunity) and slowing the spread of the virus.
The pandemic was a fast-moving situation, with new variants, uncertain global vaccine supply and the risk of sudden outbreaks. Waiting for a perfect vaccine was never a realistic option.
- There is no single best COVID-19 vaccine. It depends on what "best" means.
- Trial efficacy figures can't be compared directly, because trials took place in different places, at different times, with different variants.
- Head-to-head trials and real-world data are the fair ways to compare vaccines.
- UK data showed Pfizer and AstraZeneca both protected strongly against severe illness.
- Boosters and mixed doses help keep protection high over time.
Frequently Asked Questions
Which COVID-19 vaccine is the best?
There is no single best COVID-19 vaccine for everyone. Clinical trials and real-world data showed that all approved vaccines strongly reduced the risk of severe illness, hospitalisation and death. In practice, the best vaccine is the one recommended for you that you can get now.
What is the difference between vaccine efficacy and effectiveness?
Efficacy is how well a vaccine works in a controlled clinical trial. Effectiveness is how well it works in the real world, across the general population, where conditions are less controlled.
Why can't we compare COVID-19 vaccines using trial results?
Phase 3 trials for different vaccines were run in different countries, at different times, with different variants circulating and different groups of volunteers. Those differences make a direct comparison of their efficacy figures unreliable.
How effective were the Pfizer and AstraZeneca vaccines in trials?
In their phase 3 trials, the Pfizer-BioNTech vaccine showed about 95% efficacy against symptomatic COVID-19, while the AstraZeneca vaccine showed between 62% and 90% depending on the dosing schedule used.
Did Pfizer and AstraZeneca work equally well in the real world?
In 2021, UK real-world data showed both vaccines gave strong protection against symptomatic illness, hospitalisation and death, even after a single dose.
What is a head-to-head vaccine trial?
It is a single study that compares two vaccines directly in the same population, using the same methods. One example was a UK trial comparing the Valneva vaccine with AstraZeneca, which reported its results in October 2021.
Is it safe to mix different COVID-19 vaccines?
Studies such as Spain's CombiVacS trial in 2021 found that giving a different vaccine for a later dose was safe and produced a strong immune response. Mixing vaccines later became common for booster doses.
Should I wait for a better vaccine?
Health experts advised against waiting. Every available vaccine reduced the risk of severe disease and helped slow the spread of COVID-19 in the community. For current advice, speak to your doctor or your local health authority.
Sources: Polack et al., Safety and Efficacy of the BNT162b2 mRNA COVID-19 Vaccine, NEJM 2020 · Voysey et al., ChAdOx1 nCoV-19 vaccine interim analysis, The Lancet 2020 · UK Government: COVID-19 vaccines, further evidence of success (2021) · CombiVacS mixed-dose trial, Spain (2021) · Valneva phase 3 results vs AstraZeneca (October 2021). This article is for general information only and is not medical advice.
Post a Comment
0 Comments