When a COVID cluster includes people who are vaccinated against the virus, we inevitably hear rumblings of complaint from people who wonder what the point is of vaccination if there is no prevention.
But when you read past the headlines, you usually see the answer: in most cases, those who were vaccinated and contracted COVID-19 didn’t die, didn’t develop severe symptoms and didn’t need to be hospitalised.
For unvaccinated Australians in their later years, the chance of dying from COVID is high. For unvaccinated people in their 80s, around 32% who contract COVID will die from it. For people in their 70s, it’s around 14%. (For unvaccinated people in their 60s, it drops to around 3%. And for under-50s, it’s less than 1%.)
The good news is both Pfizer and AstraZeneca are very effective at prevention of severe disease and death from COVID-19, even from the more virulent Delta strain
So how effective are our vaccines at prevention ?
Preliminary data from the United Kingdom shows after your first dose of either Pfizer or AstraZeneca, you’re 33% less likely than an unvaccinated person to contract the Delta variant.
Two weeks after your second dose, this rises to 66% for AstraZeneca and 80% for Pfizer. This data is for any form of COVID-19, from mild to severe.
But when you look at how much the vaccines reduce your risk of developing severe illness that requires hospitalisation, the coverage is high for both. Pfizer and Astrazeneca vaccines are 96% and 92% effective (respectively) in prevention of Delta variant hospitalisations.
Why do some people still get COVID after being vaccinated?
Vaccines aren’t magic barriers. They don’t kill the virus or pathogen they target.
Rather, vaccines stimulate a person’s immune system to create antibodies. These antibodies are specific against the virus or pathogen for the vaccine and allows the body to fight infection before it takes hold and causes severe disease.
However, some people won’t have a strong enough immune response to the vaccine and may still be susceptible to developing COVID-19 if exposed to the virus.
How a person responds to a vaccine is impacted by a number of host factors, including our age, gender, medications, diet, exercise, health and stress levels.
It’s not easy to tell who hasn’t developed a strong enough immune response to the vaccine. Measuring a person’s immune response to a vaccine is not simple and requires detailed laboratory tests.
And while side effects from the vaccine indicate you’re having a response, the absence of symptoms doesn’t mean you’re having a weak response.
It also takes time for the immune system to respond to vaccines and produce antibodies. For most two-shot vaccines, antibody levels rise and then dip after the first dose. These antibodies are then boosted after the second.
But you’re not optimally covered until your antibody levels rise after the second dose.