I’m often asked how frequently or infrequently I think people are likely to need COVID-19 booster shots in the future. No one has a crystal ball to see which SARS-CoV-2 variant is next, or how well future variants will evade vaccine immunity. However, a look at other respiratory virus enemies that have been troubling humanity for some time may provide clues as to what the future may hold.
An example is the flu virus. It is endemic in humans, meaning it has not gone away and continues to cause recurrent seasonal waves of infection in the population. Every year officials try to predict the best formulation of a flu shot to reduce the risk of serious illness.
As SARS-CoV-2 continues to evolve and likely become endemic, it’s possible that people will need regular booster shots for the foreseeable future. My guess is that scientists will eventually need to update the COVID-19 vaccine to incorporate newer variants, like they do with the flu.
Prognosis of influenza based on careful surveillance
Influenza virus surveillance offers a potential model for how SARS-CoV-2 could be tracked over time. Influenza viruses have caused several pandemics, including that of 1918, which killed an estimated 50 million people worldwide. Seasonal flu outbreaks occur every year, and every year officials encourage the public to get the flu shot.
The story goes on
Each year, health authorities, including the World Health Organization’s Global Influenza Surveillance and Response System, make an educated guess based on the influenza strains circulating in the southern hemisphere as to which are most likely to circulate in the northern hemisphere during the upcoming influenza season. Then large-scale vaccine production based on the selected flu strains begins.
In some flu seasons, it turns out that the vaccine doesn’t match well with the strains of the virus that are most prevalent. In these years, the syringe is not so good at preventing serious illnesses. While this prediction process is far from perfect, the field of influenza vaccines has benefited from strong viral surveillance systems and a concerted international effort by public health officials to prepare.
While the specifics differ for influenza and SARS-CoV-2 viruses, I think the COVID-19 space should consider adopting similar surveillance systems in the long term. Keeping track of which strains are circulating will help researchers update the SARS-CoV-2 vaccine to match current coronavirus variants.
How SARS-CoV-2 has developed so far
SARS-CoV-2 faces an evolutionary dilemma as it reproduces and spreads from person to person. The virus must maintain its ability to enter human cells with its spike protein while also modifying itself in a way that allows it to evade vaccine immunity. Vaccines are designed to trick your body into recognizing a specific spike protein. So the more it changes, the higher the chance that the vaccine will be ineffective against the new variant.
Despite these challenges, SARS-CoV-2 and its variants have successfully evolved to be more transmissible and better able to evade people’s immune responses. During the course of the COVID-19 pandemic, a new worrying SARS-CoV-2 variant has emerged and has dominated transmission in a series of contagion waves every four to seven months. Almost like clockwork, variant D614G emerged in spring 2020, overtaking the original SARS-CoV-2 outbreak strain. In late 2020 and early 2021, the Alpha variant emerged and dominated the broadcast. In mid-2021, the Delta variant overtook Alpha and then dominated the transmission until it was supplanted by the Omicron variant in late 2021.
There is no reason to believe that this trend will not continue. In the coming months, the world could see a dominant progeny of the various Omicron subvariants. And it’s entirely possible that a new variant could emerge from a non-dominant pool of SARS-CoV-2, just as omicron itself emerged.
Current booster shots are just additional doses of the vaccines based on the long-extinct SARS-CoV-2 virus strain. The coronavirus variants have changed significantly from the original virus, which does not bode well for the continued effectiveness of the vaccine. The idea of tailored annual vaccinations – like the flu shot – sounds tempting. The problem is that scientists have not yet been able to predict with any certainty what the next SARS-CoV-2 variant will be.
planning for the future
Yes, the dominant SARS-CoV-2 variants in the upcoming fall and winter season may look different than the currently circulating Omicron subvariants. But an updated booster that’s more similar to today’s Omicron subvariants, combined with the immunity people already have from the first vaccines, will likely offer better protection going forward. Less frequent boosting may be required – at least as long as omicron sublines continue to dominate.
The Food and Drug Administration will meet in the coming weeks to decide what the fall boosters should be so manufacturers can get the shots made in time. Vaccine manufacturers like Moderna are currently testing their booster candidates in humans and assessing the immune response against emerging variants. Test results will likely decide what to use in anticipation of a fall or winter surge.
Another possibility is to align the vaccine booster strategy to include universal coronavirus vaccine approaches that already show promise in animal studies. Researchers are working on a so-called universal vaccine that would be effective against multiple strains. Some are focusing on chimeric spikes, which fuse parts of the spike of different coronaviruses together in a vaccine to augment protective immunity. Others are experimenting with nanoparticle vaccines that trick the immune system into targeting the most vulnerable regions within the coronavirus spike.
These strategies have been shown in laboratory experiments to repel hard-to-stop SARS-CoV-2 variants. They are also working in animals against the original SARS virus, which caused an outbreak in the early 2000s, as well as zoonotic bat coronaviruses, which could spread to humans and cause a future SARS-CoV-3 outbreak.
Science has provided several safe and effective vaccines that reduce the risk of serious illness from COVID-19. Reformulating booster strategies, either towards universal vaccines or updated boosters, can help us get out of the COVID-19 pandemic.
This article is republished by The Conversation, a nonprofit news site dedicated to exchanging ideas from academic experts. It was written by: David R. Martinez, University of North Carolina at Chapel Hill.
David R. Martinez receives funding from the National Institutes of Health, the Howard Hughes Medical Institute, and the Burroughs Wellcome Fund.