I’m often asked how often, or rarely, I think people are likely to need COVID-19 reminders in the future. No one has a crystal ball to see which variant of SARS-CoV-2 will come next or how effective future variants will be at evading vaccine immunity. But looking at other respiratory viral enemies that have troubled humanity for some time may suggest what the future might look like.
The flu virus is an example. It is endemic in humans, meaning it has not gone away and continues to cause recurring seasonal waves of infection in the population. Every year, officials try to predict the best formulation of an influenza vaccine to reduce the risk of serious illness.
As SARS-CoV-2 continues to evolve and is likely to become endemic, people may need periodic boosters for the foreseeable future. I suspect scientists will eventually need to update the COVID-19 vaccine to take new variants, as they do for the flu.
Predict the flu, based on careful surveillance
Influenza virus surveillance offers a potential model for tracking SARS-CoV-2 over time. Influenza viruses have caused several pandemics, including the 1918 pandemic that killed an estimated 50 million people worldwide. Every year there are seasonal flu epidemics and every year authorities encourage the public to get the flu shot.
Each year, health agencies, including the World Health Organization’s Global Influenza Surveillance and Response System, make an educated guess based on flu strains circulating in the southern hemisphere to determine which ones are are most likely to circulate during the upcoming Northern Hemisphere influenza season. Then, large-scale vaccine production begins, based on the selected influenza strains.
Some flu seasons, the vaccine doesn’t match very well with the viral strains that end up circulating most widely. In those years, the vaccine is not as good at preventing serious illnesses. While this prediction process is far from perfect, the flu vaccine field has benefited from strong viral surveillance systems and a concerted international effort by public health agencies to prepare.
Although the peculiarities of influenza and SARS-CoV-2 viruses are different, I think the COVID-19 field should think about adopting similar long-term surveillance systems. Staying abreast of circulating strains will help researchers update the SARS-CoV-2 vaccine to match up-to-date coronavirus variants.
How SARS-CoV-2 has evolved so far
SARS-CoV-2 faces an evolutionary dilemma as it replicates and spreads from person to person. The virus must maintain its ability to enter human cells using its spike protein, while changing in ways that allow it to evade vaccine immunity. Vaccines are designed to trick your body into recognizing a particular 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 evade people’s immune responses. During the COVID-19 pandemic, a concerning new variant of SARS-CoV-2 emerged and dominated transmission in a series of waves of contagion every four to seven months. Almost like clockwork, the D614G variant emerged in the spring of 2020 and overtook the original strain of the SARS-CoV-2 outbreak. In late 2020 and early 2021, the alpha variant appeared and dominated the transmission. In mid-2021, the delta variant overtook alpha and then dominated the transmission until it was replaced by the omicron variant in late 2021.
There is no reason to think that this trend will not continue. In the coming months, the world may see a dominant descendant of the various omicron sub-variants. And it’s certainly possible for a new variant to emerge from a non-dominant pool of SARS-CoV-2, which is how omicron itself was born.
Current booster shots are simply extra doses of vaccines based on the long-extinct SARS-CoV-2 epidemic virus strain. The variants of the coronavirus have changed significantly from the original virus, which does not bode well for the continued effectiveness of the vaccine. The idea of tailored annual vaccines – like the flu shot – sounds appealing. The problem is that scientists have not yet been able to predict what the next SARS-CoV-2 variant will be with any degree of confidence.
Plan for the future
Yes, the dominant variants of SARS-CoV-2 over the coming fall and winter seasons may look different from the omicron subvariants currently in circulation. But an updated booster that more closely resembles today’s omicron subvariants, coupled with the immunity people already have from early vaccines, will likely provide better protection in the future. This might require less frequent boosts – at least as long as the omicron sublines continue to dominate.
The Food and Drug Administration is expected to meet in the coming weeks to decide which fall boosters should be in time for manufacturers to produce the injections. Vaccine makers like Moderna are currently testing their booster candidates in humans and evaluating the immune response against newly emerging variants. Test results will likely determine what will be used in anticipation of a fall or winter surge.
Another possibility is to pivot the vaccine booster strategy to include universal coronavirus vaccine approaches that already show promise in animal studies. Researchers are working on what is called a universal vaccine that would be effective against multiple strains. Some focus on chimeric spikes, which fuse parts of the spike from different coronaviruses into a single vaccine, to broaden protective immunity. Others are experimenting with nanoparticle-based vaccines that allow the immune system to focus on the most vulnerable regions of the coronavirus spike.
These strategies have been shown to ward off hard-to-stop SARS-CoV-2 variants in laboratory experiments. They are also working in animals against the original SARS virus that caused an outbreak in the early 2000s as well as zoonotic coronaviruses from bats that could jump into humans causing a future outbreak of SARS-CoV-3. .
Science has provided several safe and effective vaccines that reduce the risk of severe COVID-19. Reformulating booster strategies, either towards universal vaccines or updated boosters, can help us emerge from the COVID-19 pandemic.
This article is republished from The Conversation, a nonprofit news site dedicated to sharing 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.