EFFICACY OF EXPECTED COVID19 VACCINE

Many of us think that the society may come to normal when the Covid 19 vaccine becomes available. According to scientists different vaccines may offer different levels of protection. It depends on the vaccine's efficacy or effectiveness. If 100 people who have not been exposed to the virus are given a vaccine that has an efficacy of 80%, that means that an average of 80 of them would not get infected. The difference between efficacy and effectiveness is that the former applies when vaccination is given under controlled circumstances, like a clinical trial,  and the latter is under 'real world' conditions. Typically, a vaccine's effectiveness tends to be lower than its efficacy.

In an epidemic or pandemic, as more people are exposed to the virus, the number of new infections per day steadily increases until it reaches a peak and begins to drop. However how long it takes depends upon how the virus and the response to it may evolve over time. To stop the pandemic, the number of new infections per day needs to drop to zero, or at least to a very low number, as quickly as possible. If the Covid 19 pandemic was just beginning and the population infected was close 0%, the simulations show that the vaccine efficacy would have to be at least 60% to stop the coronavirus if the entire population were vaccinated. If close to 0% population of a country has been infected by the time a coronavirus vaccine is ready, computer simulations show that a vaccine could eradicate the virus if the vaccine is at least 70% effective and three-quarters of the population gets vaccinated. If only 75% of the people gets vaccinated, the threshold goes even higher, to around 80% . It's all about making sure the virus can't find more people to infect. Those numbers assume that a person infected with the virus infects 2.5 other people on average. If the virus is more contagious, the vaccine has to be more efficient. Based on all findings, a vaccine with an efficacy as low as 60%  could still stop the pandemic and allow society to return to normal. However, most if not all of the population would have to be vaccinated.

(Indebted to an article published from the conversation - Bruce Y. Lee, Professor of Health Policy and Management, City University of New York)

KV George

kvgeorgein@gmail.com