The seasonal flu vaccine is often 40% to 60% effective in a given year, depending on how accurately scientists match the shots to the predominant virus strain, and public health officials still recommend it as a way to prevent millions of cases each winter.
A single dose of the measles, mumps and rubella (MMR) vaccine for young children is 93% effective against measles and 78% against mumps. A second dose raises the level of protection to 97% and 88%, respectively, helping assure parents that their children won’t suffer from illnesses that afflicted most youngsters before adolescence during the mid-20th century.
Emerging malaria vaccines have been less than 50% effective in preventing disease. The shot is hardly a silver bullet, but Gavi, the Vaccine Alliance, says malaria’s toll in Africa is so severe that “even preventing one in three cases could make a big difference.”
The COVID-19 vaccines join a long list of preventive measures that are effective but not perfect. The prominent messenger RNA shots offer more than 90% protection against severe illness, according to regulators who approved the Pfizer-BioNTech version this week.
Overall protection depends on study participants, dates and locations, but the prominent vaccines appear to be 50% to 80% effective against any infection at all.
Scientists say the combined statistical power of vaccination should be strong enough for society to make COVID-19 rare, as it has with measles, smallpox and other crippling or deadly afflictions, though it will take time.
“It’s why we no longer worry about women getting German measles or rubella and having deformed babies,” said Dr. Daniel Kuritzkes, chief of the division of infectious diseases at Brigham and Women’s Hospital in Massachusetts. “The point is with all these vaccines, once you get the vast majority vaccinated, there is no place left for the virus to go. There is not enough circulating infection to really challenge the vaccine.”
Only 51% of the U.S. population is fully vaccinated against COVID-19. Gaps in the dome of protection, combined with concerns about waning antibody responses, have given reality checks to President Biden’s promotion of the shots.
“Let me be clear: There are cases where vaccinated people do get COVID-19, but they are far less common than unvaccinated people getting COVID-19. And, most importantly, their conditions are far less severe,” Mr. Biden said in a speech praising full approval of the Pfizer vaccine on Monday.
The quickly spreading delta strain of the virus is making the challenge of fighting COVID-19 harder and increasing the bar for widespread, or “herd,” immunity close to a vaccination rate of 90%.
Shifting data on effectiveness and whether vaccinated people can still transmit the virus have implications for the increasing number of workplaces, schools and restaurants that are using mandates to help lift uptake of vaccines.
The requirements sometimes characterize vaccination as a panacea, but experts say additional safety measures would supplement protection.
“Vaccinated people were eight times less likely to get hospitalized with COVID than unvaccinated people. It doesn’t mean that protection is ironclad, but it’s really excellent,” Dr. Kuritzkes said. “Restaurant workers, in addition to being vaccinated, should be masked because protection might not be absolute, and wearing a mask provides another level of protection.”
William Schaffner, an infectious diseases specialist at Vanderbilt University, said venues should think about ways to reduce the risk of viral spread instead of declaring their environments absolutely “safe.”
“Keep the tables spread apart, reduce somewhat the clientele, the patrons that can be in there at one time. All of those things reduce the risk,” he said.
Such measures would buy time as vaccination rates improve across the country and around the world.
“Even though the protection [from the shots] is not perfect, if a large majority of the population has that protection, it really slows the virus down. That’s the public health approach. Protecting the individual who receives the vaccines is the other benefit,” Dr. Schaffner said. “The CDC has shown vaccinated and unvaccinated can have virus in their throats and be potential transmitters, but if you’re vaccinated, your duration of shedding the virus is reduced. All of these things are graduated. They’re not black and white.”
Panagis Galiatsatos, an assistant professor at Johns Hopkins School of Medicine in Baltimore, likened a vaccinated person’s immune system to a well-drilled football team that has pored over the playbook, studied film and is “ready to execute” on game day instead of one that straps on helmets and pads and wings it.
Over time, if the vaccine “converts COVID to nothing more than a common cold, that’s a win. That’s the intention of the vaccines, and the majority of vaccines,” Dr. Galiatsatos said.
“The biggest barometer has to be your hospitalizations. You’ve got to use that,” he said.
If cases increase but hospitalizations do not budge, the doctor said, “that means a lot of COVID cases you’re getting have been converted into common cold cases.”
Dr. Anthony Fauci said the U.S. can get to that point but it might take until next spring.
“Our fate is in our own hands. It probably will be, you know. I’ve said a couple of times if we do it right and get through the winter, I hope as we get to the spring of 2022, we’ll get there. I hope so. It’s up to us,” Dr. Fauci, director of the National Institute of Allergy and Infectious Diseases, told NBC’s “Today” show on Tuesday. “If we get the overwhelming majority of those 80 to 90 million people who have not yet been vaccinated, who have been reluctant to get vaccinated or have not had the opportunity, I believe we can see light at the end of the tunnel.”
Mr. Biden hopes history will serve as a guide as he pleads with Americans to roll up their sleeves and defends sweeping yet controversial mandates as a way to check the virus.
Mumps, a viral disease that primarily affects salivary glands and can result in hearing loss, was up to 150,000 cases per year when the U.S. started counting in the 1960s. The advent of a vaccine in the 1970s drove annual cases to fewer than 3,000 by 1985, according to the Centers for Disease Control and Prevention.
“The reason most people in America don’t worry about polio, smallpox, measles, mumps and rubella today is because of vaccines,” the president said Monday. “It only makes sense to require a vaccine to stop the spread of COVID-19.”