As Americans approach the six-month mark for the Covid-19 pandemic, many are wondering when their lives can return to "normal," that is, no more wearing masks, social distancing or working from home out of necessity.
Eradicating Covid-19 hinges in large part upon having a safe vaccine, which experts believe could be ready by early 2021.
But having a vaccine is just one step — it needs to be effective on a large enough percentage of the population, and enough people have to be willing to get it to truly end the pandemic.
So to find out just how effective and widely used a vaccine must be for the number of new infections per day to drop to zero, researchers used a computational model to simulate various scenarios.
The study showed that if 75% of the population gets a Covid-19 vaccine, it would need to be at least 80% effective to fully end the pandemic without any other measures. (To put this in perspective, the flu vaccination reduces the risk of flu illness by between 40% and 60%, according to the Centers for Disease Control.)
But those numbers may be unlikely. According to White House advisor Dr. Anthony Fauci, the hope is that there will be a vaccine that is at least 75% effective, though the Food and Drug Administration said in July it would authorize a Covid-19 vaccine that is at least 50% effective.
The good news is that a vaccine that has an efficacy rate between 60% and 80% could still have an impact on the pandemic, potentially reducing the need for protective measures, the study authors write.
"All of this doesn't mean that a vaccine with a lower efficacy would not be useful," Dr. Bruce Y. Lee, study author and professor at CUNY Graduate School of Public Health and Health Policy wrote for The Conversation last month. "It would mean that social distancing and mask-wearing likely would have to continue until the pandemic runs its course or a vaccine that is actually 'good enough' arrives."
According to this model, which assumes that every person with Covid-19 infects 2.5 others, if a vaccine is 60% effective, and only half of people get vaccinated, it could reduce infections by 75%. But if 100% of people get vaccinated, a vaccine that's only 60% effective could completely halt the pandemic, according to the study.
Lee said it's unlikely that 100% of people will get the vaccine, and surveys suggest that's true: A survey conducted in late July by Yahoo News and YouGov found that just 42% of Americans plan to get vaccinated for Covid-19.
There are more than 170 vaccines being developed worldwide, with at least 31 in clinical trials, according to the World Health Organization.