Why an Extra Covid Vaccine Dose May Be Needed for Some People This Spring
In October, the Centers for Disease Control and Prevention (CDC) issued an updated recommendation for high-risk individuals to consider an additional Covid vaccine dose. This new guidance specifically targets adults aged 65 and older and individuals with weakened immune systems, advising them to receive a second dose of the 2024-25 updated vaccine at least six months after their initial dose. This springtime booster aims to provide these vulnerable groups with reinforced protection against the virus.
This recommendation follows a pattern observed over the past few years. In both 2022 and 2023, the CDC authorized additional springtime doses for at-risk populations shortly after the initial rollout in the fall. For many, this frequent booster schedule may feel unusual, as no other vaccines require such regular updates. However, experts maintain that the mRNA Covid vaccines — including those from Pfizer and Moderna — remain highly effective despite the frequency of doses.
The Role of mRNA Technology in Covid Vaccines
The mRNA vaccines from Pfizer and Moderna marked a significant advancement in vaccine technology, being the first to utilize mRNA to generate immunity against a virus. This approach was instrumental during the early days of the pandemic, allowing scientists to develop and distribute effective vaccines more rapidly than traditional vaccine methods could have allowed.
Despite the CDC’s guidance for an additional dose, there’s no indication that mRNA vaccines are underperforming. According to Dr. Akiko Iwasaki, an immunology professor at Yale School of Medicine, the continued dosing may be due to the unique nature of the coronavirus, which seems to challenge the body’s ability to sustain long-term immunity. This could help explain why frequent boosters are suggested for high-risk individuals, particularly as the virus continues to mutate.
Hybrid Immunity and Covid: A Unique Challenge
Emerging research suggests that Covid-19 may interact differently with the immune system than other common viruses. A recent study conducted by Emory University researchers explored “hybrid immunity” — a state in which individuals are both vaccinated and have been infected by the virus at some point. Surprisingly, the study found that hybrid immunity did not significantly boost the production of certain long-lasting antibody-producing cells. This phenomenon stands in contrast to other viruses, such as the flu and tetanus, where hybrid immunity has been more effective in establishing these protective cells.
Dr. Iwasaki noted that this could indicate that something unique about the coronavirus is interfering with long-lasting immune responses. “You would think that hybrid immunity would be more robust, yet there was no significant increase in long-lived plasma cell numbers,” she explained, highlighting a potential reason why high-risk groups might need an extra dose this spring.
Examining the Durability of mRNA Vaccines
Questions about the durability of mRNA vaccines have also come up. Dr. Ashish Jha, dean of the Brown University School of Public Health and former White House Covid-19 response coordinator, has discussed the ongoing uncertainty around how long the immunity from these vaccines lasts compared to traditional vaccine technologies. He suggests that the mRNA vaccines may not provide as long-lasting immunity, but the exact durability remains an area of ongoing study.
In Jha’s view, however, the more pressing issue isn’t the vaccine itself but rather the virus’s ability to mutate rapidly and circulate year-round. “The problem here in my mind is not so much with the vaccine but much more with the virus,” he said, noting that he fully supports the updated recommendation for an additional dose in high-risk individuals.
Vaccine Guidance for Older Adults and Immunocompromised Individuals
One of the main concerns driving the CDC’s guidance is the potential for waning immunity, especially in older adults who are more vulnerable to severe illness. According to Dr. E. John Wherry, an immunologist at the University of Pennsylvania, topping off immunity every six to 12 months could be highly beneficial for these groups. Each booster helps elevate antibody levels, providing a stronger initial defense against infection and lessening the burden on other parts of the immune system.
By boosting antibodies regularly, high-risk individuals may experience better protection and fewer severe outcomes. “That makes it easier for the rest of your immune system to clean up and prevent that little bit of infection from causing disease,” Wherry said.
The Rapid Mutation of the Coronavirus
Unlike some other viruses, such as measles, the coronavirus continues to mutate at an accelerated pace. According to Dr. Anna Durbin, an infectious disease expert and associate professor at Johns Hopkins University School of Medicine, the speed at which Covid mutates requires more frequent vaccine updates. This rapid change presents unique challenges, as it’s difficult to develop a vaccine that perfectly matches the circulating strains at any given time.
To put this into perspective, viruses like measles do not change much over time. “A measles virus that you encounter today is very similar to one from five or ten years ago,” Dr. Jha explained. With Covid, however, the virus is constantly evolving, making it challenging for scientists to create a long-lasting vaccine.
Can Covid Vaccines Be Updated Faster?
In an ideal scenario, Covid vaccines would be adaptable enough to keep up with the virus’s rapid changes. However, there is often a lag between selecting a strain to target and the actual distribution of an updated vaccine. By the time the vaccine is produced and made available, the virus may have already mutated again.
According to Dr. Durbin, the goal is to strengthen immunity even when the vaccine strain doesn’t match the current virus perfectly. She explained, “If that immunity is boosted with another dose of the vaccine, we’ll be able to better protect those high-risk people.” Even with the rapid mutation rate, an additional dose could still offer valuable protection to individuals most at risk of severe illness.
Will Frequent Boosters Become the Norm?
For now, the CDC’s recommendation for a spring booster applies only to high-risk groups, and it’s unlikely that twice-yearly boosters will become necessary for everyone. Dr. Jha noted that the immune systems of younger individuals are typically robust enough to handle the virus without additional doses. He expressed confidence that, barring significant changes in the virus’s severity, the general population won’t require this level of frequent vaccination.
For older adults and those with compromised immune systems, however, the extra booster provides an essential line of defense as we continue to navigate the evolving landscape of Covid-19.