Glossary

Additional doses of a vaccine may be needed as part of an extended primary series for target populations where the immune response rate following the standard primary series is deemed insufficient. The objective of an additional dose in the primary series is to optimize or enhance the immune response to establish a sufficient level of effectiveness against disease. In particular, immunocompromised individuals often fail to mount a protective immune response after a standard primary series, but also older adults may respond poorly to a standard primary series.

A pharmacological agent (e.g., aluminum salt, oil-in-water emulsions) that modifies the effect of other agents, such as a drug or vaccine, while having few if any direct effects when given by itself. Adjuvants are often included in vaccines to enhance the recipient's immune response to a supplied antigen, while keeping the injected foreign material to a minimum.

Unwanted symptoms or other experiences in participants in a study, which may or may not be caused by treatments.

The vaccines are authorized in early or limited use under approve of a organization to market the drug or vaccine.

A type of error that may affect the results of a study because of weaknesses in its design, analysis or reporting

Booster doses are administered to a vaccinated population that has completed a primary vaccination series (currently one or two doses of COVID-19 vaccine depending on the product) when, with time, the immunity and clinical protection has fallen below a rate deemed sufficient in that population. The objective of a booster dose is to restore vaccine effectiveness from that deemed no longer sufficient.

A type of non-randomized study comparing the characteristics of people with a particular health condition (cases) with the characteristics of people without that condition (controls), to find what may have caused the problem

A study describing several people with a particular health condition, often covering the course of the problem before and after treatment

Clinical trials are research studies that evaluate new medical tests and treatments to determine their effects on human health. These trials follow strict protocols, require approval, and progress through four phases: Phase I tests a new treatment on a small group to determine safety and dosage; Phase II expands to a larger group to monitor side effects; Phase III involves broader populations across multiple regions to gather data for approval, and Phase IV occurs post-approval to assess long-term effectiveness and safety.

A type of non-randomized study in which defined groups of people (cohort) are followed up over time to explore the effects of treatments or other factors that may affect health outcomes

Refers to the similarity of estimates of effect across studies.

COVAX is one of three pillars of the Access to COVID-19 Tools (ACT) Accelerator, which was launched in April by the World Health Organization (WHO), the European Commission and France in response to this pandemic.

Safe and effective vaccines that prevent people from getting seriously ill or dying from COVID-19

A study measuring the distribution of a health condition, or other characteristics in a population at a particular point in time

A fluid provided in a vial or ampoule that is mixed with lyophilized vaccine powder before the vaccine can be injected. Diluents are not interchangeable. Vaccines have different diluents; mixing and administering the wrong diluent with a vaccine has led to serious adverse events including death.

Refers to the extent to which the people, interventions, and outcome measures are similar to those of interest.

DNA based-vaccine is a type of vaccine that transfects a specific antigen-coding DNA sequence onto the cells of an immunized species

The enzyme-linked immunosorbent assay (ELISA) is an immunological assay commonly used to measure antibodies, antigens, proteins and glycoproteins in biological samples

The enzyme-linked immunospot (ELISpot) assay is a highly sensitive immunoassay that measures the frequency of cytokine-secreting cells at the single-cell level

The European Medicines Agency (EMA) is a decentralised agency of the European Union (EU) responsible for the scientific evaluation, supervision and safety monitoring of medicines in the EU

An emergency use authorization is a mechanism to facilitate the availability and use of medical countermeasures, including vaccines, during public health emergencies. Vaccine developers that wish to put a vaccine on the market should request a marketing authorisation for the vaccine in the different jurisdictions. The corresponding regulatory agencies assess the safety, efficacy and quality of the vaccine and finally authorize or reject the entrance of the vaccine on the market. In response to public health emergencies, many agencies have a specific regulatory tool specifically designed to allow early availability of the product as quickly as possible. They receive different names, such as Emergency Use Authorization (EUA) in the US or Conditional Marketing Authorisation (CMA) in Europe.

The WHO Emergency Use Listing Procedure (EUL) is a risk-based procedure for assessing and listing unlicensed vaccines, therapeutics and in vitro diagnostics with the ultimate aim of expediting the availability of these products to people affected by a public health emergency

Ratio of two geometric mean titers

Geometric mean titer (GMT), is the average antibody titer for a group of subjects calculated by multiplying all values and taking the nth root of this number, where n is the number of subjects with available data.

Stands for “Grading of Recommendations Assessment, Development and Evaluation”. A system for grading the quality of evidence and the strength of recommendations that can be applied across a wide range of interventions and contexts. It stands for “Grading of Recommendations Assessment, Development and Evaluation”.

A heterologous booster refers to the administration of a vaccine product that differs from products previously used for a series of homologous or heterologous primary vaccines, once an initially sufficient immune response rate in a vaccinated population has declined over time.

In a heterologous primary schedule, the vaccine product used for the second dose differs from that used for the first dose.

Further research is very unlikely to change our confidence in the estimate of effect.

Individual Case Safety Reports

Refers to imprecise or spare data. For example if the results include just a few events or observations and they are uninformative. Or, if the confidence intervals are sufficiently wide that an estimate is consistent with either important harms or important benefits.

Inactivated vaccine is a type is a vaccine consisting of virus particles, bacteria, or other pathogens that have been grown in culture and then killed to destroy disease producing capacity.

Live attenuated virus vaccine is a type vaccines of stimulate a strong and effective immune response that is long-lasting. Given pathogens are attenuated, it is extremely rare for pathogens to revert to their pathogenic form and subsequently cause disease.

Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.

Authorization that EMA delivers for the scientific evaluation of centralized marketing authorization (MAA) applications. Once granted by the European Commission, the centralized marketing authorization is valid in one, several, or all European Union Member States.

Statistical combination of estimates derived from two or more similar studies, to give an overall effect estimate

UK's Medicines and Healthcare products Regulatory Agency

Microneutralisation test at 50%, this assay detects antibody that is capable of inhibiting virus replication (or in other words, antibody that can neutralize virus infection)

Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.

A category of studies that does not use random allocation to assign participants to treatment comparison groups

Ongoing Trial means any clinical Trial for the product where the first subject has been dosed and for which all activities related to such Clinical Trial has not reached study completion.

In studies of treatment effects, outcomes are measures of health or disease (e.g. survival, having a stroke, pain or quality of life), behaviours (e.g. smoking), or other potential benefits or harms of treatments (e.g. resource use) that affect the natural progress of the health condition that is being treated.

The Pan American Health Organization (PAHO) is the specialized international health agency for the Americas

Peripheral blood mononuclear cells (PBMCs) are blood cells with round nuclei, such as monocytes, lymphocytes, and macrophages

In this phase, the trials are performed on a large scale, after establishing a reasonable probability of efficacy of the vaccine and aim to obtain additional information on its efficacy for specific applications and a more precise definition of the adverse effects associated with the vaccine. At this stage, researchers design controlled and not-controlled clinical trials to answer specific questions about the vaccine.

In this phase, vaccines are tested on a larger group (several hundred people) to assess their efficacy and further analyze safety.

In this phase, vaccines are tested on a small group (20–80 people) to evaluate their dosage, safety and identify potential side effects.

In this phase, trials take place after a regulatory health authority, such as the U.S. Food and Drug Administration, has approved the use of the drug or vaccine. The effectiveness and safety are monitored in large, diverse populations. The aim of this stage, is to to establish the frequency of adverse reactions or determine the effects of long-term administration of a drug. Phase IV trials may also be designed to evaluate a drug in a population that has not been adequately studied in the pre-marketing phases (such as children or the elderly) or to establish a new indication for a drug.

Analyses planned before starting data collection and pre-specified in study protocols.

EMA’s Pharmacovigilance Risk Assessment Committee

A preprint is a version of a scientific manuscript posted on a public server prior to formal peer review. As soon as it’s posted, your preprint becomes a permanent part of the scientific record, citable with its own unique DOI.

Compounds that are added to multi-dose vaccine vials to prevent bacterial and fungal growth. The most commonly used product is called thiomersal, a mercury-containing compound.

Plaque-reduction neutralisation test at 50%, this assay detects antibody that is capable of inhibiting virus replication (or in other words, antibody that can neutralize virus infection)

Protein subunit vaccine is a vaccine that presents one or more antigens to the immune system without introducing pathogen particles, whole or otherwise.

Indicates the extent to which one can be confident that an estimate of effect is correct. This domain can be determined after considering each of the following elements: study design, study quality, consistency, and directness. Usually imprecision and risk of publication bias are also take into consideration.

The process of assigning participants in a study to treatment comparison groups using a chance process, like drawing lots, to protect against bias.

Una categoría de estudios que comparan dos o más tratamientos en los que se utiliza la asignación aleatoria para asignar a los participantes a los grupos de comparación de tratamientos.

A suggestion, proposal or statement to the best course of action within a clinical practice guideline. Recommendations involve a trade-off between benefits and harms.

Key features of research methods used to categorize types of studies

A systematic under-estimation or an over-estimation of the underlying beneficial or harmful effect due to the selective publication of studies.

The likelihood of an outcome in one treatment comparison group divided by the likelihood in another

RNA based vaccine is a type of genetic material from the patoghen only

WHO's Strategic Advisory Group of Experts is the principal advisory group

The term 'spot-forming cells' or SFC, is used as a quantitative measure for the number of cytokine or antibody secreting cells in the ELISPOT assay

Indicates the extent to which one can be confident that adherence to the recommendation will do more good than harm.

One for which guideline panel is confident that the desirable effects of an intervention outweigh its undesirable effects (strong recommendation for an intervention) or that the undesirable effects of an intervention outweigh its desirable effects (strong recommendation against an intervention).

Refers to basic study design, broadly categorized as observational studies and randomized trials.

Participants in a treatment study are usually patients. However, participants in studies assessing ways of preventing health conditions (e.g. to assess the effects of insecticide-treated mosquito nets to prevent malaria) are often well people; and participants in studies aiming to modify practice (e.g. to assess a strategy for implementing a guideline) may be health care providers.

A study protocol is the written description of the plans for a study. It should include references to systematic reviews of relevant existing evidence, showing that the new study is justified; the study's objectives, design, and methods; and plans for publishing the results.

Refers to the detailed study methods and execution. For randomized trials, for example, reviewers might use criteria such as the adequacy of allocation concealment, blinding, and follow up.

A variant that, according to phylogenetic analysis, belongs to a currently circulating variant of concern (VOC) and shows signals of transmission advantage compared to other circulating VOC lineages and has additional amino acid changes that are known or suspected to confer the observed change in epidemiology and fitness advantage as compared to other circulating variants. This category has been added by WHO due to the intra-VOC evolution of Omicron.

A summary of studies addressing a clear question, using systematic and explicit methods to identify, select, and critically appraise relevant studies, and to collect and analyse data from them

A titer is a measurement of the amount or concentration of a substance in a solution. It usually refers to the amount of antibodies found in a person's blood

A preparation that is used to stimulate the body’s immune response against diseases. Vaccines are usually administered through needle injections, but some can be administered by mouth (oral vaccines) or sprayed into the nose. Vaccines contain tiny fragments of the disease-causing organism or the blueprints for making the tiny fragments. They also contain other ingredients to keep the vaccine safe and effective. These latter ingredients are included in most vaccines and have been used for decades in billions of doses of vaccine. Each vaccine component serves a specific purpose, and each ingredient is tested in the manufacturing process. All ingredients are tested for safety

A technology is defined as a platform if an underlying, nearly identical mechanism, device, delivery vector, or cell line was employed for multiple target vaccines.

CDC and FDA's Vaccine Adverse Event Reporting System

For a VOC there is evidence of an increase in transmissibility, more severe disease (for example, increased hospitalizations or deaths), significant reduction in neutralization by antibodies generated during previous infection or vaccination, reduced effectiveness of treatments or vaccines, or diagnostic detection failures. In addition to the characteristics of a VOI, for a VOC there is evidence of widespread interference with diagnostic test targets, substantially decreased susceptibility to one or more class of therapies, significantly decreased neutralization by antibodies generated during previous infection or vaccination and reduced vaccine-induced protection from severe disease

VOI is a variant with specific genetic markers that have been associated with changes to receptor binding, reduced neutralization by antibodies generated against previous infection or vaccination, reduced efficacy of treatments, potential diagnostic impact, or predicted increase in transmissibility or disease severity. For a VOI there is evidence that it is the cause of an increased proportion of cases or unique outbreak clusters and also limited prevalence or expansion in the US or in other countries

VBM by the CDC are those where data indicates there is a potential or clear impact on approved or authorized medical countermeasures or that have been associated with more severe disease or increased transmission but are no longer detected, or are circulating at very low levels, in the US. These variants do not pose a significant and imminent risk to public health in the United States. A VOC or VOI may be downgraded to this list after a significant and sustained reduction in its national and regional proportions over time, or other evidence indicates that a variant does not pose significant risk to public health in the US

A variant is a viral genome (genetic code) that may contain one or more mutations (a single change in a virus’s genome that happen frequently, but only sometimes change the characteristics of the virus). In some cases, a group of variants with similar genetic changes may be designated by public health organizations as a Variant of Concern (VOC) or a Variant of Interest (VOI) due to shared attributes and characteristics that may require public health action.

Any estimate of effect is very uncertain.

Not Replicating Viral vector vaccine is a type of viral vectors provide a convenient means to deliver vaccine antigens to select target cells or tissues. A broad spectrum of replicating and non-replicating vectors is available.

Not Replicating Viral vector vaccine is a type of another virus that can copy itself carries the pathogen genes.

Virus like particle vaccine are multiprotein structures that mimic the organization and conformation of authentic viruses but lack the viral genome, potentially yielding safer and cheaper vaccine

One for which the desirable effects probably outweigh the undesirable effects (weak recommendation for an intervention) or undesirable effects probably outweigh the desirable effects (weak recommendation against an intervention) but appreciable uncertainty exists.

World Health Organization