Get an adult MMR titer or booster during the 2025 measles resurgence, or skip it?
If you act
Get an adult MMR titer or booster dose
0.001%
If you don't
Skip the titer/booster and rely on assumed childhood immunity
6.0%
Percentage who later regret each choice. Bars and full ledger render below.
Health
Get an adult MMR titer or booster during the 2025 measles resurgence, or skip it?
Last reviewed 2026-06-13
Evidence quality 4.1/5
Eight-dimension review score against the
quality rubric
. Each dimension scored 1–5.
D1 Source verification
5/5
D2 Source authority & independence
5/5
D3 Regret-rate accuracy
3/5
D4 Source comparability
3/5
D5 Gilovich pattern
4/5
D6 Prose quality
4/5
D7 Caveat completeness
4/5
D8 Sample quality
5/5
Average4.1/5
Proxy data — no direct regret survey exists for this decision. Rates are derived from satisfaction scores and access-barrier data rather than questions that directly asked about regret. See caveats below.
Action regret
Get an adult MMR titer or booster dose
0.001%
<0.001% — proxy: a serious adverse event (anaphylaxis) is the only material downside; redundancy in an already-immune adult is not a regret-worthy outcome
US adults who seek an MMR titer or a precautionary MMR dose (1963-67 killed-vaccine cohort, healthcare personnel, immunocompromised contacts) during the 2025 resurgence
Per dose administered
Inaction regret
Skip the titer/booster and rely on assumed childhood immunity
6.0%
~6% — proxy: share of a US healthcare-worker serosurvey lacking a measles immunity marker (seronegative + equivocal); an upper bound on who carries an immunity gap, not a measured regret rate
US adults in the named higher-risk cohorts (1963-67 killed-vaccine recipients, healthcare personnel, immunocompromised) who skip serologic check or revaccination during the 2025 resurgence
Cross-sectional immunity gap during the 2025 resurgence
% who regret this choice
Get an adult MMR titer or booster doseSkip the titer/booster and rely on assumed childhood immunity
0.001%6.0%
inaction dominates — Inaction dominates — most regret not acting.
No survey asks adults whether they regret getting, or skipping, a measles booster during the 2025 resurgence. The few documented post-outbreak interviews run the other way: the parents of the Texas child who died in 2025 told reporters they stood by their decision not to vaccinate. So this pair is a proxy. The action side is anchored on the probability of a serious adverse event from the shot itself, and the inaction side on the share of the relevant cohort that carries no measurable measles immunity. Neither number is a regret rate; both are stand-ins, and the gap between them is wide.
The action downside is small and well-characterized. Anaphylaxis after an MMR-containing vaccine was reported to VAERS at 0.6 per million doses over 1990 to 2016, and the CDC’s Vaccine Information Statement describes a serious reaction as a “very remote chance.” The common outcomes — a sore arm, a brief fever, a mild rash — are not the kind of thing people later regret. The subtler point is that for the large majority of adults who turn out to have been immune already, the booster was redundant rather than harmful, and a redundant-but-protective dose tends to read as reassurance, not as a mistake. That is why the action proxy sits near the floor: the only genuinely regret-worthy action outcome is the rare serious event, on the order of one in a hundred thousand or rarer.
The inaction side is where the cohorts in the question matter. A US healthcare-worker serosurvey found 4% seronegative and 2% equivocal for measles IgG — a roughly 6% immunity gap — and a 2025 meta-analysis of 23,236 vaccinated people pooled seropositivity at 87.8%, falling to 84.3% among single-dose recipients. The 1963-67 killed-vaccine cohort is a separate, smaller group that ACIP explicitly tells to revaccinate, because the inactivated product conferred little durable protection. The catch is that an immunity gap is not the same as realized regret: with 2,288 confirmed US cases in 2025 against a population of roughly 340 million, the national attack rate stayed near 0.0007%, so most seronegative adults were never exposed at all. What gives the gap its weight is the severity tail — 11% of 2025 cases were hospitalized and there were deaths — so the rare intersection of “no immunity” and “exposed” is consequential. The honest reading: skipping leaves a measurable hole in protection for a minority of these cohorts, getting the dose closes it at trivial cost, and the realized-regret asymmetry favors acting even though almost no one in either group will ever face the outcome that would make the choice matter.
Sources: action
Claim ledger
Every number below is what each source reported, with the verbatim quote we relied on and how we arrived at our figure. Click any link to verify directly.
[1]Journal of Allergy and Clinical Immunology / NCBI PMC — Anaphylaxis after vaccination reported to the Vaccine Adverse Event Reporting System, 1990–2016
Peer-reviewed
MMR-containing vaccine anaphylaxis reporting rate of 0.6 per 1 million doses distributed (overall vaccine rate 1.3 per million).
Excerpt
“The estimated rate of anaphylaxis reported to VAERS during 1990 to 2016 after MMR was 0.6 per 1 million doses distributed.”
Source data from
2019-01-01
Accessed
2026-06-13
Calculation
Anaphylaxis is the canonical serious adverse event of MMR. 0.6 per 1,000,000 doses = 6e-7. The action regret_rate is set conservatively above that floor (1e-5) to absorb other rare serious events (febrile seizure, transient thrombocytopenia) the VIS lists. The dominant 'downside' of acting for an already-immune adult is a redundant dose, which yields peace of mind rather than regret, so it is not counted as regret. This is the matched-severity proxy: action's regret-worthy outcome is a serious AE, not 'the shot turned out unnecessary'.
[2]U.S. Centers for Disease Control and Prevention — MMR Vaccine Information Statement (VIS)
Government report
Serious adverse events from MMR are characterized as a very remote chance; common effects are minor (sore arm, fever, mild rash).
Excerpt
“As with any medicine, there is a very remote chance of a vaccine causing a severe allergic reaction, other serious injury, or death.”
Source data from
2025-01-31
Accessed
2026-06-13
Calculation
Qualitative confirmation that the action side's serious downside is 'very remote.' Establishes that the regret-worthy outcome of acting is rare and severe (an AE), distinct from the common, non-regret outcome of a redundant-but-protective dose. No numeric rate on this page; the numeric anchor is PMC6580415.
Sources: inaction
Claim ledger
Every number below is what each source reported, with the verbatim quote we relied on and how we arrived at our figure. Click any link to verify directly.
[1]Infection Control and Hospital Epidemiology (PubMed) — Measles immunity in a population of healthcare workers
Peer-reviewed
Among 2,473 US healthcare workers tested for anti-measles IgG, 4% were seronegative and 2% equivocal — a ~6% immunity gap.
Excerpt
“Ninety-three workers (4%) were seronegative, and 56 (2%) were equivocal.”
Source data from
1994-01-01
Accessed
2026-06-13
Calculation
Population-matched anchor: US healthcare workers, one of the named higher-risk cohorts. Seronegative (4%) + equivocal (2%) = 6% lacking a measles immunity marker → inaction proxy 0.06. This is an immunity-gap upper bound, not a realized-regret rate: most seronegative people are never exposed (2025 national attack rate ~ 2,288 / ~340M ~ 0.0007%). The proxy measures who is even eligible for potential regret if exposed.
[2]eClinicalMedicine (The Lancet Discovery Science) — Measles seropositivity in previously vaccinated individuals: a systematic review and meta-analysis
Peer-reviewed
Pooled seropositivity among vaccinated individuals was 87.8% (so ~12.2% seronegative); single-dose recipients 84.3% seropositive (~15.7% seronegative), across 23,236 individuals from 10 countries.
Excerpt
“Pooled seropositivity was 87·8% (95% CI, 83·9%–91·2%) across 23,236 vaccinated individuals”
Source data from
2025-01-01
Accessed
2026-06-13
Calculation
Current (2025) pooled anchor confirming waning: ~12% of vaccinated adults are below seropositivity thresholds, rising to ~16% for single-dose recipients. Verified verbatim via Playwright (Lancet 403s WebFetch). Used to frame the spread; the 6% HCW figure is kept as the population-matched headline rather than the 12-16% pooled (mixed-country, assay-threshold) number to avoid overstating realized susceptibility.
[3]U.S. Centers for Disease Control and Prevention — Measles Vaccination for Specific Groups
Government report
ACIP recommends revaccinating recipients of killed/inactivated or unknown-type measles vaccine from 1963-1967; healthcare personnel without presumptive immunity need 2 doses.
Excerpt
“The ACIP recommends re-vaccinating anyone who received measles vaccine of unknown type, inactivated measles vaccine, or further attenuated measles vaccine accompanied by immunoglobulin or high-titer measles immune globulin (no longer available in the United States) during these years with 1 or 2 doses.”
Source data from
2024-07-15
Accessed
2026-06-13
Calculation
Establishes that the 1963-67 killed-vaccine cohort is functionally unprotected per ACIP and explicitly advised to revaccinate — the qualitative basis for why skipping carries downside for this cohort. This cohort is <5% of adults and overlaps the pre-1957 presumed-immune group, so it informs but does not set the numeric anchor.
[4]CDC MMWR / NCBI PMC — Measles Update — United States, January 1–April 17, 2025
Government report
Of 800 confirmed 2025 cases through April 17, 96% were unvaccinated or unknown status, 11% hospitalized, 3 deaths.
Excerpt
“Overall, 771 (96%) patients have been unvaccinated or had unknown vaccination status”
Source data from
2025-04-24
Accessed
2026-06-13
Calculation
Establishes the severity tail that makes the immunity gap consequential: 11% of measles cases hospitalized, 3 deaths in the period, 96% of cases in the unvaccinated/unknown. The realized harm to someone in the immunity gap who is exposed is severe; this is what gives the inaction proxy its weight.
[5]U.S. Centers for Disease Control and Prevention — Measles Cases and Outbreaks — 2025 Data Summary
Government report
Full-year 2025: 2,288 confirmed US measles cases — the largest annual count since 1992.
Excerpt
“For the full year of 2025, a total of 2,288 confirmed* measles cases were reported in the United States.”
Source data from
2026-06-12
Accessed
2026-06-13
Calculation
Sets the exposure backdrop: 2,288 cases / ~340M US population ~ 0.0007% national attack rate. This is why the 6% immunity-gap proxy is explicitly an upper bound on potential regret, not realized regret — exposure remained geographically concentrated and rare nationally even in the worst year since 1992.
Caveats
proxy_only: there is no direct "regret getting/skipping an MMR booster" survey; both rates are stand-ins. The inaction rate (6%) is the share of a US healthcare-worker serosurvey lacking an immunity marker (seronegative + equivocal), i.e. an upper bound on who is even eligible for regret, NOT a measured regret rate — most seronegative people are never exposed (2025 national attack rate ~0.0007%). The susceptibility spread is wide and assay-dependent: 6% (US HCW IgG), 12.2% (2025 pooled meta-analysis), up to ~37.6% in one Olmsted County, MN commercial-assay study whose high figure is largely a below-titer-threshold artifact (titer below cutoff does not equal susceptible, because anamnestic memory-B-cell immunity is not captured) and is therefore excluded from the anchor. The 1963-67 killed-vaccine cohort is <5% of adults and overlaps the pre-1957 presumed-immune group, so it is a qualitative ACIP-revaccinate flag rather than the numeric anchor. The action anaphylaxis figure (0.6/million) is a passive-surveillance VAERS reporting rate, not a measured incidence. The meta-analysis pools 10 countries, not US-only. CDC publishes immunity and case data, not regret; this entry should not be read as advice to get or skip a dose.
