Numerous efforts are underway around the world to test, manufacture, and distribute billions of doses. A table maintained by the World Health Organization (WHO) lists 33 vaccines against SARS-CoV-2, the virus that causes COVID-19, currently being tested in people, with another 143 candidates in preclinical testing.
The effort is so critical, the U.S. government is spending billions to make doses of vaccine that may be wasted if clinical trials don’t show them to be safe and effective. The goal of this massive operation, dubbed Warp Speed, is to deliver 300 million doses of safe and effective vaccines by January 2021.
As important as a vaccine will be, some experts are already trying to temper expectations for how much it will be able to do.
“We all hope to have a number of effective vaccines that can help prevent people from infection,” Tedros Adhanom Ghebreyesus, director-general of the World Health Organization, said at an Aug. 3 news briefing. “However, there is no silver bullet at the moment, and there might never be.”
Barry Bloom, PhD, an expert in infectious diseases and immunology at the Harvard T.H. Chan School of Public Health, is even more direct: The idea that a vaccine will end the pandemic just isn’t realistic.
“That’s not going to happen,” he says. First, not enough people will get the vaccine. Second, for those who do take it, the vaccine may only offer partial protection from the virus.
“I am worried about incomplete availability, incomplete protection, unwillingness of a portion of a country to be vaccinated,” Bloom says.
At least at first, not enough people will get the vaccine for the world to achieve herd immunity, or community protection. Community protection robs the virus of the chance to spread easily. It occurs when enough people become immune, either because they’ve recovered from the infection or been vaccinated against it. This high level of immunity in a population cuts the chances that someone without immunity -- say an infant or someone who can’t be vaccinated for medical reasons -- will be exposed to the virus and get sick.
Typically, the herd immunity threshold for an infection is somewhere between 70% and 90% of the population. We don’t yet know where the threshold is for COVID-19 because there are still big unanswered questions about how our bodies respond to the virus or a vaccine against it: Do most people respond in a way that protects them in the future? If so, how long does that protection typically last?
Even at the low end of the typical range for community protection -- 70% -- we’re still far short of that mark.
Recent studies checking blood samples submitted to commercial labs suggest that 5% to 10% of the population has recovered from a COVID-19 infection in the U.S. That’s just an average. The real number varies widely across the U.S., ranging from a low of about 1% in San Francisco to a high of about 20% in New York City, according to CDC data. Most of the country is still in the 3%-5% range -- still a long way from community protection against the virus.
So most of the immunity needed to reach a level that would provide community protection would have to come from a vaccine.
“It’s not just getting a vaccine. It’s using it and using it appropriately,” Bloom says. “Vaccines don't prevent anything. Vaccination does.”
A Slow Rollout
Getting enough doses to enough people will take a while, even after a vaccine becomes available, for several reasons.
When vaccines against COVID are first approved, supplies will be tight. Initially, there may be enough doses for 10 million to 15 million people in the U.S. The first shots will be reserved for the people who need them most.
Just this week, the National Academy of Sciences came up with a draft plan for how to fairly distribute the vaccine, which would unfold in four phases. Those phases will take time to execute.
The first phase recommends that the first doses go to health care workers and first responders, with the next batch going to people with health conditions that put them at highest risk of dying from COVID, and to seniors living in group homes. Those groups make up just 15% of the population, according to the report.
Phase two, which covers about 30% of the population, calls for vaccination of essential workers at “substantially high risk of exposure,” teachers, people with health conditions that put them at moderate risk from the disease, people living in close contact with others (like prisoners and those staying in homeless shelters), and seniors who weren’t covered in phase one.
The largest chunk of the population, including children, who can be infected but may show few signs of illness, aren’t a priority until phase three, which also includes other essential workers. Phase three accounts for about 40% of the population. The last phase, everyone else, makes up about 5%.
Convincing the Skeptics
Among those who are eligible for vaccination, not everyone is likely to agree to get one.
A recent poll by Gallup found that 35% of Americans -- or about one in three -- don’t plan on getting a COVID-19 vaccine, even if it’s free. Among the two-thirds of Americans who say they will be immunized, a large number plan to wait. A recent survey by STAT found that 71% will wait at least 9 months to get their shots.
Those numbers align with a recent poll by WebMD, which found that 73% of readers said they would wait at least 3 months to get a vaccine when one becomes available.
“I don’t find that shocking. I would think for people who are rational, wouldn’t you want to see what the data are on safety and efficacy before you made a decision?” Bloom says. “I’m worried about the 25% who, no matter what happens, won’t take the vaccine. Those are the people who really worry me.”
Vaccine hesitancy -- fear of getting any vaccine -- is growing. The WHO recently listed it as one of the top threats to global health, pointing to the recent resurgence in measles. Many countries have recently seen large outbreaks of measles. These outbreaks have been caused by an increasing number of parents refusing to vaccinate their kids.
Experts are worried that vaccine hesitancy will play a large role in whether the U.S. and other countries reach herd immunity thresholds. The Gallup poll found Republicans are less likely to be vaccinated than Democrats, and nonwhite Americans -- the group being disproportionately affected by COVID-19 infections -- are less likely to be vaccinated than whites.
Bloom and others believe that right now, we should be working on a way to overcome vaccine hesitancy.
“Policymakers have to start focusing on this,” says Robert Litan, PhD, JD, a nonresident senior fellow at the Brookings Institute.
He thinks we shouldn’t try to overcome hesitancy by forcing people to take the vaccine. Instead, he wants the government to pay people to take it -- $1,000 each, or $4,000 for a family of four.
“That’s a lot of money,” especially now with the economy sagging and so many people out of work, Litan says. “I think a thousand dollars would get a lot of people to take the shot who would otherwise not take it.”
Litan ran the numbers, looking at various scenarios of how many people would take it and how effective the vaccine might be. He says he realized not enough people would be protected to fully reopen the country.
He says he’s not sure $1,000 is the right sum, but it should be generous because if people think the amount could go up, they will wait until it does, which would defeat the purpose of the incentive.
“I can’t think of anything else,” he says. “You either have carrots or sticks, and we can’t use sticks. It won’t work.”
How Well Will It Work?
Getting enough people to take it is only one piece of the puzzle. We still don’t know how well any of the shots might work, or for how long that protection lasts.
Researchers have now confirmed at least four cases of COVID-19 reinfection, proving that the virus infected the same person twice.
We still don’t know how common reinfection is, but these cases suggest that some people may need a booster dose of vaccine before they’re fully protected against the virus, says Gregory Poland, MD, an expert in immunity and vaccine responses at the Mayo Clinic in Rochester, MN.
That’s similar to the way we dole out vaccines for seasonal flu, with people urged to get the shot every year, he says.
That’s another reason it could take a while to reach herd immunity.
It’s also not clear how effective a vaccine may be.
The FDA and WHO have said that a vaccine should be at least 50% more effective than a placebo to be approved. But that could mean that a shot merely decreases how bad an infection is but doesn’t stop it. That would be an important effect, Bloom says, but it could mean that even vaccinated people would continue to spread the infection.
“If it prevents disease, but doesn’t prevent growth in the upper respiratory tract, there is a possibility there will be a group of people who will be infected and not get sick because of the vaccine but still have the virus in their respiratory tract and be able to transit,” Bloom says. “That would not be the ideal for a vaccine, but it would protect against disease and death.”
He says the first studies will probably measure how sick vaccinated people get and whether or not they need to be hospitalized.
Longer studies will be required to see if vaccinated people are still able to pass the virus to others.
How effective any vaccine may be will also depend on age. In general, older adults -- the ones who most need protection against COVID-19 -- don’t respond as well to vaccines.
Our immune systems get weaker as we get older, a phenomenon called immunosenescence.
Seniors may need specially formulated vaccines -- with added ingredients, called adjuvants -- to get the same response to vaccines that a younger person might have.
Lastly, there’s the problem of reintroduction. As long as the virus continues to spread anywhere in the world, there’s a risk that it could reenter the U.S. and reignite infections here.
That’s what happens every year with measles. In most states, more than 90% of people are vaccinated against measles. The measles vaccine is one of the most effective ever made. It gives people substantial and long-lasting protection against a highly contagious virus that can stay in the air for long periods. You can catch it by walking through the same room an infected person was in hours before.
Every year, travelers come to the U.S. carrying measles. If they go to a crowded place, like a theme park, it increases the chances that initial infection will touch off many more. As vaccine hesitancy has increased in the U.S. and around the world, those imported cases have sparked outbreaks that have been harder and harder for public health officials to extinguish, raising the risk that the measles virus could become endemic again in countries like the U.S.
For the world to be rid of COVID-19, most of the world has to be vaccinated against it. There’s an effort underway -- called COVAX -- to pay for vaccinations for poorer countries. So far, 76 of the world’s wealthier countries have chipped in to fund the effort. The U.S. has not. The Trump administration says it won’t join because of the WHO’s involvement in the effort, a move that may place the plan in jeopardy.
For all these reasons, it will probably be necessary to continue to spread out, wear masks, and be vigilant with hand hygiene to protect yourself and others for the foreseeable future.
“For now, stopping outbreaks comes down to the basics of public health and disease control,” Tedros said.
We may get a vaccine, but we will still need to be able to test enough people for the virus, warn their contacts, and isolate those who are infectious to keep the epidemic under control, or, as Tedros has urged, “Do it all.”