Keeping up with the COVID-19 vaccines means getting three or four doses of the same shot at this point. The current boosters are the same formulations used in the first authorized shots, based on the original strain of the coronavirus that emerged in late 2019. They still protect against severe COVID-19, hospitalizations and deaths.
But as immunity wanes over time and new, more infectious variants of SARS-CoV-2 emerge, the world needs a long-term boosting strategy.
I am an immunologist who studies immunity to viruses. I was part of the teams that helped develop Moderna and Johnson & Johnson SARS-CoV-2 vaccines, and monoclonal antibody therapies from Eli Lilly and AstraZeneca.
I am often asked how often or rarely I think people are likely to need COVID-19 booster injections in the future. Nobody has a crystal ball to know which SARS-CoV-2 variant will come next or how good future variants will be at evading vaccine immunity. But looking at other respiratory virus enemies that have plagued humanity for a while can suggest what the future might look like.
The influenza virus provides one example. It is endemic to humans, which means it has not gone away and continues to cause frequent seasonal waves of infection in the population. Each year, officials try to anticipate the best formulation of the flu vaccine to reduce the risk of severe illness.
As SARS-CoV-2 continues to evolve and is likely to become epidemic, people will likely need periodic booster doses for the foreseeable future. I suspect that eventually scientists will need to update the COVID-19 vaccine to deal with newer variants, as they do with influenza.
Influenza prediction based on close monitoring
Monitoring for influenza viruses offers a potential model for how to track SARS-CoV-2 over time. Influenza viruses have caused many pandemics, including in 1918 which killed an estimated 50 million people worldwide. There are seasonal flu outbreaks every year, and every year officials encourage the public to get flu shots.
Each year, health agencies, including the WHO’s Global Influenza Surveillance and Response System, make an informed guess based on which influenza strains are circulating in the Southern Hemisphere about which ones are most likely to circulate in the next influenza season in the Northern Hemisphere. Then mass production of the vaccine begins, based on the selected influenza strains.
In some flu seasons, the vaccine doesn’t turn out to closely match the strains of the virus that eventually circulate widely. In those years, the shot wasn’t very good at preventing severe disease. While this prediction process is far from perfect, the field of influenza vaccine has benefited from robust viral surveillance systems and a concerted international effort by public health agencies to prepare.
While the details of influenza viruses and SARS-CoV-2 are different, I think the COVID-19 field should consider adopting similar surveillance systems in the long term. Staying abreast of the strains in circulation will help researchers update the SARS-CoV-2 vaccine to match recent coronavirus variants.
How has SARS-CoV-2 evolved so far
SARS-CoV-2 faces an evolutionary quandary as it reproduces and spreads from person to person. The virus needs to maintain its ability to get into human cells with its spike protein, while still changing in ways that allow it to evade vaccine immunity. Vaccines are designed to make your body recognize a specific protein, so the more you change, the greater 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 to better evade people’s immune responses. Over the course of the COVID-19 pandemic, a worrying new type of SARS-CoV-2 emerged and dominated transmission in a series of waves of infections every four to seven months.
Just like the clock mechanism, the D614G variant appeared in the spring of 2020 and bypassed the original SARS-CoV-2 outbreak strain. In late 2020 and early 2021, an alpha variant emerged and dominated the transmission. In mid-2021, the delta variant overtook alpha and then dominated transmission until it was displaced by the omicron variant at the end of 2021.
There is no reason to believe that this trend will not continue. In the coming months, the world may see a dominant descendant of several omicron sub-variants. It is certainly possible that a new variant from a non-dominant group of SARS-CoV-2 may have appeared, which is why the omicron itself appeared.
The current booster shots are just additional doses of vaccines based on the outbreak of the long-extinct strain of SARS-CoV-2. The coronavirus variants have changed a lot from the original virus, which does not bode well for the vaccine’s continued effectiveness. The idea of specially designed annual vaccinations – such as the flu shot – sounds appealing. The problem is that scientists have not yet been able to predict what the next variant of SARS-CoV-2 will be with any degree of confidence.
Planning for the future
Yes, the dominant SARS-CoV-2 variants in the upcoming fall and winter seasons may look different from the currently circulating omicron sub-variants. But an updated boost that is very similar to today’s omicron sub-variants, combined with the immunity people already have from the first vaccines, is likely to provide better protection in the future. It may require less frequent reinforcement – at least as long as the Omicron subspecies continues to dominate.
The Food and Drug Administration is set to meet in the coming weeks to decide what fall boosters should be in time for manufacturers to produce the shots. Vaccine makers such as Moderna are currently testing their booster candidate in people and evaluating the immune response against newly emerging variants. Test results are likely to determine what will be used in anticipation of the fall or winter hike.
Another possibility is to direct the vaccine enhancement strategy to include approaches to a global coronavirus vaccine that already appear promising in animal studies. Researchers are working on a so-called universal vaccine that is effective against multiple strains.
Some are focusing on dummy mutations, which combine parts of the spike in different coronaviruses together into one vaccine, to expand protective immunity. Others are experimenting with nanoparticle vaccines that cause the immune system to focus on the most vulnerable areas within the coronavirus spike.
These strategies have been shown to ward off SARS-CoV-2 variants that are difficult to stop in lab experiments. They also work in animals against the original SARS virus that caused the outbreak in the early 2000s as well as zoonotic coronaviruses from bats that could jump to humans, causing future outbreaks of SARS-CoV-3.
Science has offered multiple safe and effective vaccines that reduce the risk of severe COVID-19 infection. Reframing booster strategies, whether toward universal vaccines or updated boosters, can help guide us out of the COVID-19 pandemic.
David R. Martinez, Postdoctoral Fellow in Epidemiology, University of North Carolina at Chapel Hill.
This article has been republished from The Conversation under a Creative Commons license. Read the original article.