While the world is looking to vaccinations to end the COVID pandemic, a MedPage Today article explains that even with vaccines that have high efficacy, ending transmission is not guaranteed, and there are a lot of differences between simple figures like 94% for Pfizer and 95% for Moderna vaccines.
Firstly, asymptomatic cases are not tracked, simply because assembling tens of thousands of people for a clinical trial is a monumental logistic task, and in the current pandemic, a race against time.
Internist Jeffrey Carson, MD, who managed the Johnson & Johnson COVID vaccine trial’s site at Rutgers University in New Jersey, explained to MedPage Today that it would be difficult but not impossible to create a vaccine trial that provided rapid data about asymptomatic cases.
“You might have people swab themselves every couple days, or every week. You’ll be picking up a lot of disease that way, and you’ll be able to see if the vaccine prevents asymptomatic disease,” Dr Carson said. The current Novavax trial, for example, only asks participants to test themselves for COVID with provided swabs if they believe they are developing symptoms. The Novavax vaccine had also prompted alarm as it was only 49.4% effective against the B501Y.V2 variant, its efficacy reduced by the low rate of protection for HIV positive participants.
The New York Times explained that efficacy is merely how well a vaccine did in a clinical trial, effectiveness is how well it performs in the real world.
Vaccine statistics are difficult even for medical experts to grasp. An infectious diseases expert wrote in a letter to the Lancet explaining that they had misunderstood what 94% to 95% efficacy means for Moderna and Pfizer vaccines and asymptomatic spread.
“It does not mean that 95% of people are protected from disease with the vaccine — a general misconception of vaccine protection.” Instead, it “means that in a population such as the one enrolled in the trials, with a cumulated COVID-19 attack rate over a period of 3 months of about 1% without a vaccine, we would expect roughly 0.05% of vaccinated people would get diseased [with symptomatic infections]. … Accurate description of effects is not hair-splitting; it is much-needed exactness to avoid adding confusion to an extraordinarily complicated and tense scientific and societal debate around COVID-19 vaccines.”
A further problem for scientists is that viral diseases can spread to people unaware that they are infected, something they are still working on understanding. “It makes a lot of sense for survival of the invaders, if you think about it. Humans who feel unwell are not going out to meet up with others, but ones who feel fine will continue along with their daily schedules, allowing the infection to spread,” Bryn Boslett, MD, an infectious disease physician at the University of California San Francisco, told MedPage Today.
Regardless of how well vaccines interrupt the transmission of COVID, it’s important that mask-wearing, social distancing and disinfecting habits are maintained.
“One major worry going forward is that vaccinated people will change their behaviour and stop taking COVID-19 precautions,” Dr Boslett said. “It’s very tempting to do so, very understandable. However, the stars are not yet aligned for us to go back to ‘normal.’ There is still a lot of COVID-19, and most of us are still vulnerable. We need to continue to focus on behavior to reduce new cases of COVID-19.”
Source: MedPage Today
