Current CDC Recommendations for Older Adults
For the 2024-2025 respiratory virus season, the Centers for Disease Control and Prevention (CDC) recommends that all adults aged 65 and older receive two doses of the updated mRNA COVID-19 vaccine. The CDC does not state a preference for either the Pfizer or Moderna vaccine, emphasizing that both are effective and safe for this demographic. This recommendation reflects the increased risk of severe illness, hospitalization, and death that older adults face from COVID-19, and the need for continued protection as immunity wanes over time.
Staying up to date with vaccination is a critical preventative measure, and for many seniors, the choice between Pfizer and Moderna comes down to what is most readily available and comfortable. However, specific clinical studies have provided additional insights that can be helpful for those weighing their options with a healthcare provider.
Comparative Studies: Effectiveness and Adverse Events in Seniors
While large-scale clinical trials initially showed comparable high effectiveness rates for both Pfizer and Moderna, real-world data and later head-to-head comparative studies focusing specifically on older adults have revealed some distinctions.
Findings from Key Research
- Brown University / JAMA Network Open Study (2023): In a large-scale head-to-head comparison involving over 6 million older adults (average age 76), researchers found that while the risk of serious adverse events was very low for both, the Moderna vaccine was associated with slightly fewer negative side effects than Pfizer. Specifically, those who received the Moderna vaccine had a 4% lower risk of pulmonary embolism and a 2% lower risk of thromboembolic events. The study also found that Moderna was associated with a 14% lower risk of contracting COVID-19 in this age group.
- National Centre for Infectious Diseases Study (2025): Recent research has also explored immune response following booster shots. A study from the NCID found that in participants over 60 who initially received Pfizer, a Moderna booster resulted in significantly higher antibody levels compared to a Pfizer booster.
- Differences in Frailty: Researchers in the Brown University study noted that the observed differences between the two vaccines became less pronounced in the most frail older adults. This suggests that a person's overall health status and immune response capacity can influence the comparative performance of the vaccines.
Potential Explanations
One possible reason cited for the differences observed in these studies, particularly the stronger immune response from Moderna, is the higher dosage of its vaccine. While the original Pfizer doses were 30 μg, Moderna's were 100 μg, which may have produced a more robust and lasting antibody response in older immune systems, which are known to be less responsive to vaccination. The higher dose may also account for the slightly higher reactogenicity (short-term side effects like fever or fatigue) often observed with Moderna, though this is generally well-tolerated and short-lived.
Comparison of Pfizer vs. Moderna for Seniors
Here is a side-by-side comparison of the key characteristics of the Pfizer and Moderna mRNA vaccines, particularly relevant for older adults.
| Feature | Pfizer-BioNTech (Comirnaty) | Moderna (Spikevax) |
|---|---|---|
| Current Formulation | Updated 2024-2025 version targets currently circulating strains. | Updated 2024-2025 version targets currently circulating strains. |
| Effectiveness | High effectiveness against severe disease and hospitalization. Earlier comparative studies in seniors suggest slightly lower effectiveness against infection than Moderna. | High effectiveness against severe disease and hospitalization. Some studies suggest slightly higher effectiveness against infection, particularly with earlier variants and initial doses. |
| Immune Response | Robust, but potentially less potent initial antibody response in older adults compared to Moderna due to lower dosage. | Robust, with some studies showing a stronger initial antibody response in older adults, possibly due to a higher dose. |
| Side Effects (Seniors) | Very low risk of serious adverse events. Some studies suggest a slightly higher risk of minor adverse events like pulmonary embolism and blood clots compared to Moderna. | Very low risk of serious adverse events. Some studies suggest a slightly lower risk of adverse events compared to Pfizer in older adults. |
| Dosage | Traditionally a lower mRNA dose (e.g., 30 μg in original formulation). | Traditionally a higher mRNA dose (e.g., 100 μg in original formulation). |
| CDC Recommendation | Recommended, no preference over other available options. | Recommended, no preference over other available options. |
| Booster Response | Effective, but one study showed lower antibody levels in older adults boosted with Pfizer compared to Moderna. | Effective, with one study showing higher antibody levels in older adults boosted with Moderna compared to Pfizer. |
Making an Informed Decision
The decision of which vaccine to receive should always involve a discussion with a healthcare provider, especially for older adults with underlying health conditions or frailty. While both vaccines are excellent choices for preventing severe COVID-19, certain factors might influence a personal preference.
Factors to consider:
- Availability: The most important factor is often accessibility. Getting the vaccine that is available to you is the best and most immediate protection against serious illness.
- Underlying Health: For individuals with a history of specific conditions, a healthcare provider might have a nuanced perspective based on their knowledge of your medical history. Remember, vaccine adverse events are rare, but comparing minor risks may be relevant for some.
- Frailty Level: As observed in the Brown study, the differences in effectiveness between the vaccines diminish in the most frail individuals. For those with increased frailty, the choice may be less critical, and getting any recommended updated vaccine is key.
- Immune Response History: If you are an older adult who has previously received primary doses or boosters of one brand and experienced a good response, you may choose to continue with that brand, although mixing and matching boosters is common practice and also effective.
Conclusion: Both Offer Strong Protection
Ultimately, the takeaway for older adults and their families is that both Pfizer and Moderna offer strong, effective protection against severe illness and death from COVID-19. The CDC's stance of no preference should be reassuring, as it indicates a high level of confidence in both products. While some older studies suggest potential minor advantages for Moderna in terms of adverse events and immune response in seniors, the most important step is to follow the current CDC recommendations and stay up to date with the latest vaccines, regardless of brand.
Consulting with your doctor is the best way to determine the optimal immunization strategy for your specific health needs.
For the latest official recommendations and guidance from the CDC, please visit the CDC website.
