JUST as the COVID-19 second wave started subsiding, there’s an apprehension of a third wave striking India, as has been the case in some other countries. Kerala, in particular, is witnessing a surge in number of COVID cases over the past few days.
VACCINE EFFICACY & EFFECTIVENESS
COVID-19 vaccines have proven to be safe, effective and life-saving. Like all vaccines, they do not fully protect everyone who is vaccinated, and we do not yet know how well they can prevent people from transmitting the virus to others. But vaccination is the best option available to avert COVID-19.
All COVID-19 vaccines approved by WHO for emergency use have been through randomised clinical trials to test their quality, safety and efficacy. To be approved, vaccines are required to have a high efficacy rate of 50% or above. After approval, they continue to be monitored for ongoing safety and effectiveness. But what is the difference between efficacy and effectiveness?
A vaccine’s efficacy is measured in a controlled clinical trial and is based on how many people who got vaccinated developed the disease compared to how many people who got the placebo (dummy vaccine) developed the same outcome. From this we get the efficacy – a measure of the extent to which a vaccine lowers the risk of getting sick.
So, for example, let’s imagine a vaccine with a proven efficacy of 80%. This means that – out of the people in the clinical trial – those who received the vaccine were at an 80% lower risk of developing the disease than the group which received the placebo. An efficacy of 80% does not mean that 20% of the vaccinated group will become ill.
Vaccine effectiveness is a measure of how well vaccines work in the real world. Effectiveness is measured by observing how well the vaccines work to protect communities as a whole. Effectiveness in the real world can differ from the efficacy measured in a trial, because we cannot predict exactly how effective vaccination will be for a much bigger and more variable population getting vaccinated in more real-life conditions.
VACCINE PROTECTION & DURATION
Vaccines offer strong protection, but that protection takes time to build. People must take all the required dosage of a vaccine to build full immunity. For two-dose vaccines, vaccines only give partial protection after the first dose, and the second dose increases that protection. For a one-dose vaccine, people will have built maximum immunity against COVID-19 a few weeks after getting vaccinated.
The COVID-19 vaccines can stop most people from getting sick with COVID-19, but not everyone. Even after someone takes all of the recommended dosage and waits a few weeks for immunity to build up, there is still a chance that they can get infected. Vaccines do not provide 100% protection, so ‘breakthrough infections’ – where people get the virus, despite having been fully vaccinated – will occur.
If vaccinated people get sick, they are likely to have milder symptoms. It is very rare for someone vaccinated to experience severe illness or die from the disease s/he is vaccinated against.
