Do mRNA and non-mRNA 2025 COVID-19 boosters differ in side-effect profiles across ages?

1. What the public guidance and product mix say — two platforms in use

U.S. public health guidance and vaccine program pages describe two vaccine platforms in current use: mRNA vaccines from Moderna and Pfizer‑BioNTech and a protein subunit vaccine from Novavax (Nuvaxovid) for 2024–25 and into 2025, with updated formulations targeted to circulating variants ^{[4] [1] [5]}. Yale Medicine and CDC materials confirm the availability of both mRNA and non‑mRNA options and note ongoing updates and deliberations about recommendations for fall 2025 ^{[6] [1]}.

2. Common, short‑term side effects — patterns that cross vaccine types

Observational and cohort studies repeatedly list the same common short‑term reactions for mRNA boosters: local injection‑site pain, fatigue, headache and general aches, typically lasting one to two days ^[2]. Clinical‑care pages and institutional guidance also emphasize that serious adverse events are rare and that routine side effects are usually short lived and manageable ^{[7] [8]}.

3. Where non‑mRNA (Novavax) appears to differ — fewer immediate systemic reactions

Multiple journalistic and scientific accounts report that Novavax’s protein‑subunit booster tends to produce fewer immediate systemic reactions compared with mRNA boosters — for example, lower rates of fever, nausea, muscle fatigue and other transient symptoms in the first 48 hours — although it is not symptom‑free ^{[9] [3] [10]}. WebMD summarized comparative studies showing Novavax recipients reported fewer post‑boost side effects but in at least one analysis had higher rates of infection than mRNA recipients ^[9].

4. Myocarditis/pericarditis — a rare age‑ and sex‑skewed risk linked mainly to mRNA shots

CDC safety pages and analyses indicate myocarditis and pericarditis have been observed rarely after COVID‑19 vaccines, occurring most frequently in adolescent and young adult males after mRNA doses, particularly within a week of the second mRNA dose; those events have been a focus of monitoring and discussion ^[11]. ScientificAmerican and other reviews state that compared with mRNA vaccines, Novavax appears to have a lower risk of myocarditis/pericarditis — though “lower” does not mean zero risk ^[3].

5. Age differences — what the sources support and what they don’t

Sources clearly state young males (adolescents/young adults) show the highest relative risk for mRNA‑associated myocarditis/pericarditis ^[11]. Beyond that, cohort studies emphasize that common reactogenic symptoms (fatigue, local pain, headache) occur across ages and typically last 1–2 days after mRNA boosters ^[2]. However, the provided sources do not supply a comprehensive, head‑to‑head, age‑stratified comparison of 2025 mRNA versus non‑mRNA booster side‑effect profiles across all age groups — that granular breakdown is not found in current reporting (not found in current reporting).

6. Tradeoffs and competing perspectives

Reporting highlights tradeoffs: some analyses find Novavax causes fewer short‑term reactions but in some studies showed higher infection rates compared with mRNA boosters, suggesting lower reactogenicity does not necessarily equal stronger or longer protection ^{[9] [3]}. Public‑health voices (CDC, Yale Medicine) emphasize that benefits of updated boosters generally outweigh the risks of side effects and that choice of vaccine may consider individual risk tolerance and clinical history ^{[4] [12]}.

7. Limitations, uncertainties and what to watch for

Available sources include observational cohorts, regulatory summaries and journalism but do not provide a single, large randomized, age‑stratified head‑to‑head safety analysis of the 2025 updated mRNA versus Novavax boosters; therefore precise age‑specific differences in side‑effect incidence for 2025 boosters remain incompletely characterized in this set of reporting (not found in current reporting). Ongoing CDC surveillance, FDA package inserts and forthcoming studies (and ACIP presentations) are the likely places to find updated age‑stratified safety numbers as they are published ^{[11] [4]}.

Bottom line: the evidence provided shows a consistent pattern — mRNA boosters produce the common short‑term reactogenic symptoms across ages and have a rare myocarditis signal concentrated in younger males; Novavax/protein‑subunit boosters tend to cause fewer immediate systemic reactions and may have lower myocarditis risk but may differ in effectiveness in some analyses — yet detailed, 2025-specific, age‑by‑age comparative rates are not available in the sources reviewed ^{[2] [3] [9] [11] [4]}.