Understanding the Efficacy of the COVID-19 Vaccine
Bouve/ChE University Distinguished Professor Mansoor Amiji explains how the COVID-19 vaccine is designed to prevent severe illness, hospitalization, and death, rather than to eliminate infection entirely.
Why do some vaccines (polio, measles) prevent diseases, while others (COVID-19, flu) only reduce their severity?
When the first vaccines for COVID-19 rolled out in December 2020, some people hoped they would be a silver bullet against the novel virus the way that polio and smallpox shots are nearly 100% effective against those diseases.
Instead, the updated COVID vaccine is being compared to the flu vaccine in the sense that its goal is to prevent severe disease, hospitalization and death rather than to eliminate infection entirely.
That doesn’t mean the COVID and flu vaccines are failures, health experts at Northeastern say.
Mansoor Amiji, university distinguished professor of pharmaceutical sciences and chemical engineering, and Neil Maniar, professor of the practice in public health, say vaccines differ according to whether the viruses they’ve been designed to quell are mutating or stable.
Stable versus mutating viruses
The measles and polio viruses are stable and don’t mutate over time, Amiji says. The same is true for the virus for smallpox, which has been eradicated globally and only exists in the lab.
Making a vaccine with an antigen from a stable virus means a vaccinated person’s immune system is primed to recognize and destroy the virus every time it appears, Amiji says.
“If you start to see an outbreak of polio, in any part of the world, these vaccines are still incredibly effective. If the virus crops up, it won’t evade the immune system or evade the vaccine’s response,” he says.
Such is not the case with influenza, the virus that causes flu, and SARS-CoV-2, the virus that causes COVID-19.
COVID-19 has gone through an alphabet soup of strains, from the Alpha to Beta, Delta, Omicron, Pirola and Eris — and is still evolving.
“Even though we have so many people either having natural infection or who have been vaccinated, these viruses continue to mutate,” Amiji says.
“We’re making vaccines that are looking for the spike proteins in the virus and are basically teaching our immune cells to look for the spike protein. But if the spike protein is mutating, then the vaccine efficacy starts to wane,” he says.
Influenza mutates even faster, which is why there are new flu vaccine formulas every year and why 50% is considered a good efficacy rate, he says.
The combinations of antigenic proteins on the influenza surface, known as hemagglutinin and neuraminidase — the H and N in virus nomenclature — vary year to year and even within the flu season, Amiji says.
The flu vaccine is “made up of a cocktail of these peptides,” he says. “It’s really a guessing game. There is no way of knowing which strain will be prevalent and which vaccines will work,” he says.
‘Wild to mild’ campaign manages expectations
That rate is making the flu vaccine a harder sell among the public.
The Centers for Disease Control and Prevention says during a year with a good match, vaccination reduces the risk of flu illness by between 40% and 60% among the overall population.
Consumer research shows “that many people believe flu vaccination doesn’t work because of first- or second-hand experience where vaccination may not have prevented illness,” the CDC says.
Read full story at Northeastern Global News