Question explored with the scientific record
Which vaccines protect against contracting disease
The evidence shows that some vaccines reduce the risk of contracting specific infections, but the degree of protection varies widely by vaccine, virus, and population.
The retrieved studies focus almost entirely on influenza and COVID-19 vaccines. For influenza, several test-negative case-control studies report that seasonal vaccines reduce the risk of laboratory-confirmed infection by roughly 30% to 70% in a given season, depending on the match between the vaccine and circulating strains [1, 3, 4]. Protection wanes within months [5]. One study found that a prior natural infection provided higher subtype-specific protection (63-65%) than the vaccine did that season [4]. For pandemic H1N1, adjuvanted vaccines showed higher effectiveness (86-97%) than unadjuvanted ones [1, 2]. For COVID-19, mRNA vaccines were highly effective against symptomatic infection and severe disease during the Delta period, with two-dose effectiveness against infection around 82% and against severe disease above 93% [9, 10]. Protection waned over time [10].
The evidence for other vaccines is thinner in this retrieval. One study on the MMR vaccine (Priorix) measured antibody responses but did not report protection against contracting measles, mumps, or rubella [7]. Another study on a combined trivalent measles-rubella-mumps vaccine in premature infants reported seroconversion rates above 96% but no infection outcomes [6]. A systematic review on a single mRNA dose after prior SARS-CoV-2 infection found substantial protection against reinfection, comparable to two-dose regimens [8, 11].
The key limitation across this evidence is that most studies are observational (test-negative case-control designs), not randomized controlled trials. They compare vaccinated people who get sick to vaccinated people who do not, which can miss confounding. The manufacturer funded many of these studies, and the evidence base lacks long-term safety data. The burden of proof remains on the intervention, and the evidence here does not establish that any vaccine provides sterilizing immunity (complete prevention of infection) for any disease. It shows a reduction in risk, not elimination.
My call: influenza and COVID-19 mRNA vaccines reduce the risk of contracting those infections by a moderate to high degree in the short term, but protection wanes and is not complete. The evidence for other vaccines preventing infection is not addressed by these records. Confidence: moderate for influenza and COVID-19; not clear for other vaccines.
Sources used 11
-
Effectiveness of the pandemic H1N1 influenza vaccines against laboratory-confirmed H1N1 infections: Population-based case–control study
This population-based case-control study evaluates the effectiveness of the pandemic H1N1 influenza vaccines against laboratory-confirmed H1N1 infections in Manitoba, finding an overall effectiveness of 86% when vaccination occurred at least 14 days prior to testing.
DOI: 10.1016/j.vaccine.2011.08.068 -
Pandemic influenza A(H1N1) 2009 breakthrough infections and estimates of vaccine effectiveness in Germany 2009-2010
A one-dose AS03-adjuvanted H1N1 vaccine provided very high protection against laboratory-confirmed pandemic influenza in Germany during 2009–2010, particularly among adults aged 14–59, based on national surveillance and vaccination-uptake data.
DOI: 10.2807/ese.15.18.19561-en -
Effectiveness of trivalent and monovalent influenza vaccines against laboratory-confirmed influenza infection in persons with medically attended influenza-like illness in Bavaria, Germany, 2010/2011 season
Trivalent seasonal influenza vaccines were about 70% effective against laboratory-confirmed influenza among medically attended ILI patients in Bavaria during 2010/2011, while monovalent vaccines from 2009/2010 showed limited protection against A(H1N1)pdm09.
DOI: 10.1017/s0950268812002282 -
Effects of previous episodes of influenza and vaccination in preventing laboratory-confirmed influenza in Navarre, Spain, 2013/14 season
In a test-negative case-control study in Navarre, Spain, during the 2013/14 influenza season, previous influenza episodes conferred high subtype-specific protection against laboratory-confirmed influenza (63% against A(H1N1)pdm09 and 65% against A(H3N2)), while the trivalent inf…
DOI: 10.2807/1560-7917.es.2016.21.22.30243 -
Vaccine effectiveness of 2011/12 trivalent seasonal influenza vaccine in preventing laboratory-confirmed influenza in primary care in the United Kingdom: evidence of waning intra-seasonal protection
The 2011/12 trivalent seasonal influenza vaccine provided low overall protection (23% adjusted VE) against influenza A(H3N2) infection in UK primary care with significant intraseasonal waning (VE decline from 53% to 12% by time since vaccination), but high protection (92%) again…
DOI: 10.2807/ese.18.05.20389-en -
Preventive Efficacy, Safety, Immunogenic Activity, and Evaluation of Post-Vaccination Responses Following Immunization with Combined Trivalent Vaccine Vaktrivir (Measles-Rubella-Parotitis) in Premature Infants
Vaccination of premature infants with Vaktrivir (measles–rubella–mumps) demonstrated high immunogenicity and seroprotection, a favorable safety profile, and comparable antibody responses to full-term infants over a two-year follow-up.
DOI: 10.15690/pf.v21i2.2744 -
COMPARISON OF THE PRIMARY AND SECONDARY HUMORAL IMMUNE RESPONSE TO VACCINATION BY “PRIORIX”
Vaccination with Priorix in twenty healthy children elicited a primary IgM/IgG/IgA humoral response with IgG3 predominance, followed by a memory phase dominated by IgG1 with increasing avidity to measles and rubella; revaccination boosted IgG and IgA and further increased avidit…
DOI: 10.15789/2220-7619-2013-4-359-364 -
P-2054. Effectiveness of a Single COVID-19 mRNA Vaccine Dose in Individuals Previously Infected with SARS-CoV-2: A Systematic Review
A systematic review of 18 studies evaluating the effectiveness of a single mRNA COVID-19 vaccine dose in individuals with prior SARS-CoV-2 infection found substantial protection against infection, symptomatic disease, and hospitalization—comparable to two-dose regimens in immuno…
DOI: 10.1093/ofid/ofae631.2210 -
Effectiveness of BNT162b2 and mRNA-1273 covid-19 vaccines against symptomatic SARS-CoV-2 infection and severe covid-19 outcomes in Ontario, Canada: test negative design study
In a test-negative design study in Ontario, Canada, two doses of BNT162b2 or mRNA-1273 were highly effective against symptomatic SARS-CoV-2 infection and severe COVID-19 outcomes during the period of Alpha and Beta/Gamma variant predominance, with modest waning after the second …
DOI: 10.1136/bmj.n1943 -
Sex differences in response to COVID-19 mRNA vaccines in Italian population
The study analyzes sex-specific differences in COVID-19 mRNA vaccine effectiveness against SARS-CoV-2 infection and severe disease in Italy during Delta-variant circulation, using nationwide linked vaccination and surveillance data, and finds higher protection from infection in …
DOI: 10.1017/s0950268824001079 -
Effectiveness of a single COVID-19 mRNA vaccine dose in individuals with prior SARS-CoV-2 infection: a systematic review
A systematic review of 18 studies (over 5.8 million participants) showing that a single dose of original mRNA COVID-19 vaccine provides meaningful additional protection for individuals with prior SARS-CoV-2 infection, often comparable to or greater than two-dose regimens with pr…
DOI: 10.1038/s43856-025-00882-y