It's a conundrum for vaccine researchers and producers alike: what's the best strategy for vaccinating against a deadly virus if the immune system will forget how to protect itself against it a year later?
Recent research that suggests that novel coronavirus immunity doesn't last very long have thrown a wrench in the global plans to develop and roll out a vaccine. The duration of protective immunity, which is how long a person is naturally protected from the coronavirus following an infection, is believed to be anywhere between four to twelve months at the moment, based on current research.
Since the coronavirus which causes COVID-19 is so new to science, it is still impossible to study long-term immunity using human data just yet. However, as Salon has previously reported, a conservative prediction suggests that a previously-infected person is immune to the coronavirus for at least three months. More recently, researchers published a study in the scientific journal Nature Medicine suggesting that people who contract the novel coronavirus and then become immune may stay that way for up to twelve months, based on studying four different seasonal coronaviruses.
Neither of these are definitive, but whether immunity lasts three months, one year, or even slightly longer, the evidence points to the conclusion that immunity protection is temporary.
"I think right now the data really supports and is strongly pointing to, but not proving, to the possibility that protection is likely not to be lifelong," Dr. Charles Chiu, a professor of infectious diseases at the University of California–San Francisco, told Salon.
Some viruses, such as measles, confer lifelong immunity on those who have either contracted them or been vaccinated against them. Not so with coronavirus. The science suggests that coronavirus contraction (and thus likely vaccination, too) provides what is known as "transient immunity."
The missing detail regarding how long one is immune leaves humanity with a lot of uncertainty around how we will adapt to life with the coronavirus, and what role the vaccine will play in our lives.
"This may end up being a vaccine that's not a one-time thing or even a two-time thing, it may end up being like, one time and a booster, or it may end up being what we call either a seasonal vaccine, or vaccine that needs to be administered every couple of years," Chiu said.
Chiu added that we already have precedents set for this type of virus, so it's not unheard of for a vaccine to require patients to receive regular updates and boosters. For example, the influenza vaccine is given every year. Physicians recommend that people receive tetanus shots every 10 years after the initial tetanus series. For diphtheria, booster shots are recommended every 10 years, too.
Understanding how often humans will have to get the coronavirus vaccine raises "real questions," Chiu said, about who gets the vaccine once it's available. Part of that is because it may take years for enough vaccines to be produced to inoculate the majority of the population. If the vaccine only confers temporary immunity, that could mean that billions of doses would need to be produced every year, and the populace inoculated again and again, which would require an unparalleled industrial operation.
"We're going to need to prioritize in terms of who gets the vaccine and target who gets vaccinated," Chiu said. "We'd probably prioritize the more vulnerable members of our society, elderly persons with comorbidities, etcetera, and then health care workers who are at higher risk or essential workers who may be at higher risk, then we'd need to expand our capacity so we can then provide the vaccine to the rest of the population."
Transient immunity could make it harder for the United States to achieve herd immunity, Chiu said.
"It really depends on how transient it is, and how rapidly we can really ramp up to be able to vaccinate a sufficient proportion of the population to develop herd immunity," Chiu said, adding that vaccine hesitancy is another barrier if multiple doses are needed of the coronavirus vaccine. "We already have issues right now with adherence to the flu vaccine, and there's no reason to think that it's going to be different."
Bunny Ellerin, the director of the healthcare and pharmaceutical management program at Columbia Business School, told Salon she believes that by 2021 the United States will have a couple of approved vaccines and more data on what immunity looks like. She added that while there's a benefit to having multiple vaccines produced by different companies, that doesn't necessarily reduce the resources needed to produce and distribute the vaccine en masse.
"Overall, having to produce this much of a vaccine — it's still taking resources away from something else," Ellerin said.
There are over 100 vaccine candidates in development around the world, and many are progressing at an unprecedented pace compared to normal vaccine development cycles.
As of September 22, according to the New York Times Coronavirus Vaccine Tracker, there are 40 different vaccine candidates worldwide that have already reached the clinical trial phase. Additionally, there are at least 92 preclinical vaccine trials happening on animals, which means the vaccine is being administered to animals like mice or monkeys to see if it produces an immune response. One promising vaccine, which is a collaboration between BioNTech and Pfizer, has published research that shows the mRNA-based vaccine produces antibodies against SARS-CoV-2 and T-cells that respond to the virus. This means that the mRNA, which is genetic material from the coronavirus, evokes an immune response.
Another promising vaccine, created by Moderna, is in the third and final phase of clinical trials and has emerged as a top contender. For the Moderna vaccine, published research shows in small trials after a second shot of the vaccine all the participants developed neutralizing antibodies. For the Pfizer vaccine, a strong activation of T cells was found which is believed to prevent people from getting reinfected. Both require two doses.
Notably, the presence of antibodies does not always mean that a neutralizing antibody response will occur (meaning that antibodies circulate in the body and prevent reinfection). However, a cellular-mediated immune response can prevent reinfection, which is a type of immune response that has nothing to do with antibodies. In other words, Chiu says, transient immunity does not necessarily mean that reinfection will occur, as cellular immunity could play a role, too.
While there have been three cases of patients who had been previously afflicted by COVID-19 contracting the virus a second time, Chiu said that such cases would likely be more prevalent in the United States if not for some other mediating factor. He believes it is possible that cellular immunity plays a role in preventing reinfection.
Having a complete picture of duration of immunity will in turn affect how inoculations are recommended, who receives priority to receive the vaccine, and how containment measures are deployed to keep the coronavirus at bay.
Doctors have already warned policy makers to consider protective immunity when figuring out how to adapt to a world with COVID-19. Likewise, as antibody tests become more prevalent, a positive antibody test will no longer be considered a marker of immunity to the coronavirus.
Chiu said we are now facing a "race against time," especially when you factor in that the coronavirus might mutate. He was hopeful that a combination of containment strategies, like wearing masks, social distancing and getting vaccinated, will eventually eradicate the coronavirus.
"The hope is that the vaccine, while it may not be 100 percent effective or durable, is enough so that then, if we have enough testing and containment measures in place, we can simply eradicate the virus," Chiu said.