Study findings updated . AI-assisted evidence summary, not individual medical advice or a clinician endorsement.
Key findings
99.84% tolerated dose 2Pooled share with no severe reaction to dose 2 after an immediate reaction to dose 1
After an allergic reaction to a first dose, severe repeats were rare.
Among people who had an immediate allergic reaction to a first mRNA COVID shot, 99.84% got through the second dose without a severe reaction, though 13.65% had mild symptoms. Among those whose first reaction was severe, 4.94% had another severe one. Skin testing, split dosing and premedication (medicine taken beforehand) did not change the results.
A frightening first-dose reaction usually did not make the next dose dangerous. That matters for anyone told to stop vaccinating after one reaction, and it suggests routine allergy tests add little to the decision. Pooled case series and case reports, mostly in women; certainty was moderate overall but low for people whose first reaction was severe.
Systematic review and meta-analysis of 22 studies covering 1,366 people with an immediate allergic reaction to a first mRNA COVID shot, searched through October 2021.
From the study: “232 developed mild symptoms (13.65% [95% CI, 7.76%-22.9%]), and, conversely, 1360 tolerated the dose (99.84% [95% CI, 97.09%-99.99%])”
99.84% tolerated dose 2
Chu DK et al. Risk of Second Allergic Reaction to SARS-CoV-2 Vaccines: A Systematic Review and Meta-analysis. JAMA internal medicine. 2022.
From the study: “Among 78 persons with severe immediate allergic reactions to their first SARS-CoV-2 mRNA vaccination, 4 people (4.94% [95% CI, 0.93%-22.28%]) had a second severe immediate reaction”
99.84% tolerated dose 2
Chu DK et al. Risk of Second Allergic Reaction to SARS-CoV-2 Vaccines: A Systematic Review and Meta-analysis. JAMA internal medicine. 2022.
From the study: “Graded vaccine dosing, skin testing, and premedication as risk-stratification strategies did not alter the findings.”
99.84% tolerated dose 2
Chu DK et al. Risk of Second Allergic Reaction to SARS-CoV-2 Vaccines: A Systematic Review and Meta-analysis. JAMA internal medicine. 2022.
1 in 130,000 dosesFrom the pooled rate of 7.91 anaphylaxis cases per million COVID vaccine doses
Anaphylaxis after COVID vaccines was very rare, with no reported anaphylaxis deaths.
Pooling 26 studies covering 41 million vaccinations, anaphylaxis (a severe, whole-body allergic reaction) occurred at 7.91 cases per million doses, and no deaths from anaphylaxis were reported. A skin test for PEG, a vaccine ingredient, had poor sensitivity, meaning it misses many true allergies, though that evidence was of very low certainty.
Fear of a severe reaction keeps some people from getting vaccinated. These numbers put that risk in perspective, and they show why a quick skin test is not a reliable way to screen people before a shot. Pooled reports up to March 2021; the authors note anaphylaxis definitions varied across countries and organizations, which complicates comparisons.
Systematic review and meta-analysis by an international expert panel, pooling reports on about 41 million COVID vaccinations through March 2021.
From the study: “The incidence of SARS-CoV-2 vaccine anaphylaxis is 7.91 cases per million (n = 41,000,000 vaccinations; 95% confidence interval [95% CI] 4.02-15.59; 26 studies, moderate certainty)”
1 in 130,000 doses
Greenhawt M et al. The Risk of Allergic Reaction to SARS-CoV-2 Vaccines and Recommended Evaluation and Management: A Systematic Review, Meta-Analysis, GRADE Assessment, and International Consensus Approach. The journal of allergy and clinical immunology. In practice. 2021.
From the study: “the meta-analyzed incidence of anaphylaxis was 7.91 per million (95% confidence interval [95% CI 4.02-15.59), and no anaphylaxis-related fatalities were reported.”
1 in 130,000 doses
Greenhawt M et al. The Risk of Allergic Reaction to SARS-CoV-2 Vaccines and Recommended Evaluation and Management: A Systematic Review, Meta-Analysis, GRADE Assessment, and International Consensus Approach. The journal of allergy and clinical immunology. In practice. 2021.
From the study: “the sensitivity for PEG skin testing is poor, although specificity is high (15 studies, very low certainty)”
1 in 130,000 doses
Greenhawt M et al. The Risk of Allergic Reaction to SARS-CoV-2 Vaccines and Recommended Evaluation and Management: A Systematic Review, Meta-Analysis, GRADE Assessment, and International Consensus Approach. The journal of allergy and clinical immunology. In practice. 2021.
125% higher asthma riskHazard ratio 2.25 for a new asthma diagnosis after COVID vs uninfected people
Having COVID was linked to a higher risk of new asthma.
Compared with uninfected people, those who had COVID had a 20% higher hazard of a new allergic disease beyond the first 30 days, and a 2.25-fold hazard of new asthma. Eczema (atopic dermatitis) and food allergy showed no significant rise. At least two vaccine doses were linked to lower risk of later allergic disease.
It suggests COVID can leave lasting effects on the airways and immune system. New wheezing, cough or breathlessness in the months after infection may deserve a look for asthma rather than being written off. Observational adult cohorts in South Korea, Japan and the UK; the authors note that existing but undiagnosed asthma may have been misclassified as new.
Matched cohort study of national insurance records for 836,164 South Korean adults in 2020 to 2021, with replication in Japanese records and the UK Biobank.
From the study: “The risk of developing allergic diseases, beyond the first 30 days of diagnosis of COVID-19, significantly increased (HR, 1.20; 95% CI, 1.13-1.27), notably in asthma (HR, 2.25; 95% CI, 1.80-2.83)”
125% higher asthma risk
Oh J et al. Incident allergic diseases in post-COVID-19 condition: multinational cohort studies from South Korea, Japan and the UK. Nature communications. 2024.
From the study: “no significant risk was observed in atopic dermatitis (AD; HR, 1.15; 95% CI, 0.96 to 1.37) and food allergy (FA; HR, 0.85; 95% CI, 0.71 to 1.00)”
125% higher asthma risk
Oh J et al. Incident allergic diseases in post-COVID-19 condition: multinational cohort studies from South Korea, Japan and the UK. Nature communications. 2024.
From the study: “COVID-19 vaccination of at least two doses had a protective effect against subsequent allergic diseases (HR, 0.81; 95% CI, 0.68-0.96)”
125% higher asthma risk
Oh J et al. Incident allergic diseases in post-COVID-19 condition: multinational cohort studies from South Korea, Japan and the UK. Nature communications. 2024.
35% vs 24% hospitalizedWithin 30 days of a COVID diagnosis: penicillin label 34.8% vs no label 23.8%
A penicillin allergy label was linked to more COVID hospital stays.
Among adults with COVID, those whose records carried a penicillin allergy label were hospitalized more often than matched patients without one: 34.8% vs 23.8%. Deaths did not differ significantly. The paper notes that most people with the label are not truly allergic; fewer than 10% test positive.
A chart label that is usually wrong went along with sicker COVID courses. That turns an old, unchecked allergy note into something worth questioning, though this study cannot say whether removing a label changes outcomes. Observational study of records from 48 US health care organizations, January 2020 to January 2021; it cannot show the label itself caused worse outcomes.
Retrospective cohort study in the TriNetX health-records network comparing 13,183 COVID patients with a penicillin allergy label to 13,183 matched patients without one.
From the study: “4591 of the PCN-allergic patients (34.8%) required hospitalization, compared with 3136 patients without PCN allergy (23.8%; RR = 1.46; 95% CI, 1.41-1.52; P < .001)”
35% vs 24% hospitalized
Kaminsky LW et al. Penicillin Allergy Label Increases Risk of Worse Clinical Outcomes in COVID-19. The journal of allergy and clinical immunology. In practice. 2021.
From the study: “however, there was no mortality difference (RR = 1.09; 95% CI, 0.96-1.23)”
35% vs 24% hospitalized
Kaminsky LW et al. Penicillin Allergy Label Increases Risk of Worse Clinical Outcomes in COVID-19. The journal of allergy and clinical immunology. In practice. 2021.
From the study: “most patients with PCN allergy label do not have the allergy after undergoing further evaluation, and less than 10% of patients with documented PCN allergy test positive”
35% vs 24% hospitalized
Kaminsky LW et al. Penicillin Allergy Label Increases Risk of Worse Clinical Outcomes in COVID-19. The journal of allergy and clinical immunology. In practice. 2021.
50% lower infection riskAdjusted hazard ratio 0.50 for people reporting doctor-diagnosed food allergy
Food allergy was linked to lower infection risk; asthma showed no link.
In regularly swabbed households, people who reported doctor-diagnosed food allergy had half the hazard of catching the virus compared with those who did not. Doctor-diagnosed asthma, nasal allergies such as hay fever, and eczema showed no increase in infection risk.
Early fears that asthma made catching COVID likelier were not borne out in this careful swabbing study. The food allergy finding is a clue researchers want to explain, not a reason for anyone to change what they do. Self-reported diagnoses in 18 cohorts from 12 US cities, May 2020 to February 2021, before vaccines and variants; observational, so it cannot prove cause.
Prospective surveillance study of 4,142 people in 1,394 US households enriched for asthma and allergy, with nasal swabs every 2 weeks for 6 months.
From the study: “Self-reported doctor-diagnosed food allergy was associated with lower infection risk (aHR = 0.50 [95% CI = 0.32-0.81])”
50% lower infection risk
Seibold MA et al. Risk factors for SARS-CoV-2 infection and transmission in households with children with asthma and allergy: A prospective surveillance study. The Journal of allergy and clinical immunology. 2022.
From the study: “Self-reported doctor-diagnosed asthma was not a risk factor for infection (adjusted hazard ratio [aHR] = 1.04 [95% CI = 0.73-1.46]), nor was upper respiratory allergy or eczema.”
50% lower infection risk
Seibold MA et al. Risk factors for SARS-CoV-2 infection and transmission in households with children with asthma and allergy: A prospective surveillance study. The Journal of allergy and clinical immunology. 2022.
16.1× risk after ModernaRelative risk vs a Pfizer booster in the national cohort; 20.8 in the regional one
Moderna boosters were linked to much higher risk of new chronic hives.
Among people who developed chronic spontaneous urticaria (CSU, itchy hives that keep returning with no outside trigger), symptoms began a median 10 to 11 days after vaccination. Compared with a Pfizer-BioNTech booster, a Moderna booster was linked to a relative risk of 20.8 in a regional cohort and 16.1 in a larger national one.
Hives that start about 10 days after a booster and keep coming back may be tied to the shot, a pattern patients and doctors can recognize. The brand difference is a lead for researchers and for future booster planning. Swiss case cohorts without general-population baseline rates for hives; the authors flag selection bias and possible confounding by the Omicron wave.
Two Swiss case cohorts of 80 regional and 782 nationwide patients who developed chronic hives around their COVID booster, compared by vaccine brand.
From the study: “Compared with the Pfizer-BioNTech vaccine, the relative risk of developing CSU after the Moderna vaccine was 20.8 (95% CI, 6.5-66.0) in the CSU-Vaud cohort”
16.1× risk after Moderna
Duperrex O et al. Incidence of Chronic Spontaneous Urticaria Following Receipt of the COVID-19 Vaccine Booster in Switzerland. JAMA network open. 2023.
From the study: “and 16.1 (10.8-24.0) in the CSU-Swiss cohort”
16.1× risk after Moderna
Duperrex O et al. Incidence of Chronic Spontaneous Urticaria Following Receipt of the COVID-19 Vaccine Booster in Switzerland. JAMA network open. 2023.
From the study: “The median (IQR) time between vaccination and CSU onset was 10 (8-12) days in the CSU-Vaud cohort and 11 (9-13) days in the CSU-Swiss cohort.”
16.1× risk after Moderna
Duperrex O et al. Incidence of Chronic Spontaneous Urticaria Following Receipt of the COVID-19 Vaccine Booster in Switzerland. JAMA network open. 2023.
0% vs 2.9% egg allergyEgg allergy at 24 months: lockdown-born babies vs a pre-pandemic group
Babies born in lockdown had less egg allergy but more eczema.
At 24 months, none of the babies born during lockdown had egg allergy, versus 2.9% in a pre-pandemic group. Milk and peanut allergy were also lower, but those gaps were not statistically clear. Atopic dermatitis (eczema) was more common: 21.3% vs 15.9% at 24 months.
It hints that a baby's earliest surroundings can push allergy risk in different directions at once, a useful clue for researchers working out how to prevent food allergy. Observational study of 365 Irish infants born March to May 2020, compared with an earlier Irish infant cohort; it cannot show which lockdown changes mattered.
Irish birth cohort study following 365 babies born in the first 2020 COVID lockdown to age 2, with skin prick tests and eczema checks.
From the study: “There was less milk (0% vs. 1%; p = .09), peanut (0.6% vs. 1.8%; p = .3), and egg allergy (0% vs. 2.9%; p < .001) in the CORAL group at 24 months compared with the BASELINE cohort.”
0% vs 2.9% egg allergy
Hurley S et al. Atopic outcomes at 2 years in the CORAL cohort, born in COVID-19 lockdown. Pediatric allergy and immunology : official publication of the European Society of Pediatric Allergy and Immunology. 2023.
From the study: “AD was more common in CORAL group at both 12 (26.5% vs. 15.5%; p < .001) and 24 months (21.3% vs. 15.9%; p = .02) compared with pre-pandemic BASELINE cohort.”
0% vs 2.9% egg allergy
Hurley S et al. Atopic outcomes at 2 years in the CORAL cohort, born in COVID-19 lockdown. Pediatric allergy and immunology : official publication of the European Society of Pediatric Allergy and Immunology. 2023.
778 adults: gain fadedTrial size; a small 12-week fatigue drop vanished 12 weeks after the drugs stopped
Famotidine-loratadine eased long COVID fatigue slightly, but not after stopping.
In a randomized trial in long COVID, daily famotidine plus loratadine (two antihistamines, sold as Pepcid and Claritin) lowered fatigue slightly more than no study drug at 12 weeks. Fatigue fell in every group, even with no drug. Twelve weeks after the pills stopped, fatigue scores no longer differed between groups.
People with long COVID want to know whether everyday allergy pills help. Here the effect was small and did not outlast the pills, and fatigue eased in every group, a reminder that improvement alone does not prove a drug worked. Open-label trial, so patients knew their group, run in 12 UK NHS long COVID clinics among people never hospitalized for COVID.
Randomized four-arm trial of 778 adults with long COVID in the UK, 2022 to 2024, testing colchicine, rivaroxaban or famotidine-loratadine against no drug for 12 weeks.
From the study: “Of 6035 eligible participants, 778 (383 co-enrolled in the ICP trial and 395 directly enrolled in the drug trial) were randomly assigned”
778 adults: gain faded
STIMULATE-ICP consortium. Efficacy and safety of rivaroxaban, colchicine, and famotidine-loratadine with specialist supportive clinical care for fatigue in patients with post-COVID-19 condition in the UK: a multisite, open-label, randomised controlled trial. The Lancet. Infectious diseases. 2026.
From the study: “severe fatigue reduced in all study groups-including the no drug group-over 12 weeks, with small additional reductions in the colchicine and famotidine-loratadine groups”
778 adults: gain faded
STIMULATE-ICP consortium. Efficacy and safety of rivaroxaban, colchicine, and famotidine-loratadine with specialist supportive clinical care for fatigue in patients with post-COVID-19 condition in the UK: a multisite, open-label, randomised controlled trial. The Lancet. Infectious diseases. 2026.
From the study: “However, 24-week FAS scores, 12 weeks after drug cessation, were not significantly different between groups.”
778 adults: gain faded
STIMULATE-ICP consortium. Efficacy and safety of rivaroxaban, colchicine, and famotidine-loratadine with specialist supportive clinical care for fatigue in patients with post-COVID-19 condition in the UK: a multisite, open-label, randomised controlled trial. The Lancet. Infectious diseases. 2026.
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[1]
Chu DK et al. Risk of Second Allergic Reaction to SARS-CoV-2 Vaccines: A Systematic Review and Meta-analysis. JAMA internal medicine. 2022.
Greenhawt M et al. The Risk of Allergic Reaction to SARS-CoV-2 Vaccines and Recommended Evaluation and Management: A Systematic Review, Meta-Analysis, GRADE Assessment, and International Consensus Approach. The journal of allergy and clinical immunology. In practice. 2021.
Oh J et al. Incident allergic diseases in post-COVID-19 condition: multinational cohort studies from South Korea, Japan and the UK. Nature communications. 2024.
Kaminsky LW et al. Penicillin Allergy Label Increases Risk of Worse Clinical Outcomes in COVID-19. The journal of allergy and clinical immunology. In practice. 2021.
Seibold MA et al. Risk factors for SARS-CoV-2 infection and transmission in households with children with asthma and allergy: A prospective surveillance study. The Journal of allergy and clinical immunology. 2022.
Duperrex O et al. Incidence of Chronic Spontaneous Urticaria Following Receipt of the COVID-19 Vaccine Booster in Switzerland. JAMA network open. 2023.
Hurley S et al. Atopic outcomes at 2 years in the CORAL cohort, born in COVID-19 lockdown. Pediatric allergy and immunology : official publication of the European Society of Pediatric Allergy and Immunology. 2023.
STIMULATE-ICP consortium. Efficacy and safety of rivaroxaban, colchicine, and famotidine-loratadine with specialist supportive clinical care for fatigue in patients with post-COVID-19 condition in the UK: a multisite, open-label, randomised controlled trial. The Lancet. Infectious diseases. 2026.
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