Measuring COVID-19 vaccines effectiveness (VE)

Cohort study to measure COVID-19 vaccine effectiveness among health workers

Health workers in participating hospitals, eligible for vaccination, with no contraindication to receive COVID-19 vaccine


Primary objectives:

  • To measure product-specific COVID-19 vaccine effectiveness (VE) amongst hospital health workers eligible for vaccination against all laboratory-confirmed SARS-CoV-2 infection

Secondary objectives (depending on sample size)

  • To measure COVID-19 VE:
    • against symptomatic laboratory-conformed COVID-19 infection
    • against asymptomatic laboratory-confirmed COVID-19 infection
    • against severe laboratory-confirmed COVID-19 infection
    • by time since vaccination
    • by different age groups
    • by different high-risk comorbidities
    • previous SARS-CoV-2 infection
    • by HW occupation and/or ward
    • patient-facing vs. non-patient-facing HWs
    • in individuals who have been partially vaccinated (one dose for most COVID-19 vaccines) compared to those who are fully vaccinated (two doses for most COVID-19 vaccines)

Measuring COVID-19 vaccines effectiveness (VE)

Protocol for a case-control study

Question/ population:
severe acute respiratory infections (SARI) hospitalisations associated with laboratory-confirmed SARS-CoV-2



Primary objective:

  • To measure overall COVID-19 vaccine effectiveness (CVE) against laboratory-confirmed SARS-CoV-2 in hospitalised SARI patients belonging to the target group(s) for COVID-19 vaccination.

Secondary objectives:

  • To estimate overall and product-specific CVE against laboratory-confirmed SARS-CoV-2 requiring hospitalisation among SARI patients in vaccination target groups by:
    • age group
    • sex
    • risk group (e.g. specific chronic conditions)
    • time since vaccination
    • in persons who have received one dose of vaccine compared to those who have received two doses
    • specific SARS-CoV-2 genetic variant(s)
  • To estimate CVE for more severe outcomes (e.g. ICU admission, or in-hospital mortality)
  • To identify potential factors that may modify CVE: chronic medical conditions, influenza vaccination, living in a long-term care facility (LTCFs), receiving statins or other long-term medication (depending on availability of these data in the participating country), and higher risk of exposure to SARS-CoV-2.
Population-based age-stratified seroepidemiological investigation protocol for COVID-19 infection
Question/ population:
Virus infection in the general population 
  Primary objectives:

  • To measure the seroprevalence of antibodies to COVID-19 in the general population by sex and age group, in order to ascertain the cumulative population immunity; and
  • To estimate the fraction of asymptomatic, pre-symptomatic or subclinical infections in the population and by sex and age group.

Secondary objectives, such as, but not limited to:

  • To determine risk factors for infection by comparing the exposures of infected and non-infected individuals;
  • To contribute to determine the case fatality ratio; and
  • To contribute to an improved understanding of antibody kinetics following COVID-19 infection.
The First Few COVID-19 X cases and contacts transmission investigation protocol (FFX)
Question/ population:
Cases and close contacts in the general population or
can be restricted to semi-close settings (like households, health care settings, schools).

The primary objectives are to provide descriptions or estimates of :

  • clinical presentation of COVID-19 infection and course of associated disease;
  • secondary infection rate (SIR) and secondary clinical attack rate of COVID-19 infection among close contacts (overall, and by key factors such as setting, age and sex, for various end-points);
  • serial interval of COVID-19 infection;
  • symptomatic proportion of COVID-19 cases (through contact tracing and laboratory testing); and identification of possible routes of transmission.
  • identification of possible routes of transmission

The secondary objectives are to support the estimation of:

  • the basic reproduction number (R0) of COVID-19 virus;
  • the incubation period of COVID-19; and
  • the preliminary COVID-19 infection and disease-severity ratios (for example, case‑hospitalization ratio [CHR] and case-fatality ratio [CFR]).
Household transmission of COVID-19 investigation protocol (HH)
Question/ population: Cases and close contacts in household setting

Primary objectives:

  • To better understand the extent of transmission within a household by estimating the secondary infection rate for household contacts at an individual level, and factors associated with any variation in the secondary infection risk.
  • To characterize secondary cases including the range of clinical presentation, risk factors for infection, and the extent and fraction of asymptomatic infections
  • To characterize serologic response following confirmed COVID-19 infection
Assessment of COVID-19 risk factors among Health Workers (HW)

Prospective study of a cohort of health workers)
Question/ population:
All health workers in a health care setting in which patient(s) with a laboratory-confirmed COVID-19 infection are receiving care








Protocol for a case-control study
Question/ population:
Health workers exposed to COVID-19 patients 

Primary objectives:

  • To better understand the extent of human-to-human transmission among health workers by estimating the secondary infection rate[1] for health worker contacts at the individual level.
  • To characterize the range of clinical presentations of infection and the risk factors for infection among health workers.
  • To evaluate the effectiveness of infection prevention and control measures among health workers.
  • To evaluate the effectiveness of infection prevention and control programmes at health facility and national level.

Secondary objectives such as, but not limited to:

  • To determine the serological response of health workers with symptomatic and possibly asymptomatic COVID-19 infection;
  • To characterize the duration and severity of COVID-19-associated disease among health workers.



The primary objective of this case-control study among health workers is:

  • to characterize and assess the risk factors for SARS-CoV-2 infection in health workers exposed to COVID-19 patients.

The secondary objectives of the study are:

  • to evaluate the effectiveness of current COVID-19 IPC measures among health workers;
  • to describe the range of clinical presentation for SARS-CoV-2 infection in health workers, including disease duration and outcome; and
  • to determine serological responses in health workers with confirmed SARS-CoV-2 infection following exposure to COVID-19 patients, and in those exposed to COVID-19 patients but without SARS-CoV-2 infection.


Schools and other educational institutions transmission investigation protocol for COVID-19
Question/ population:
Students and staff of schools and other educational institutions with a laboratory confirmed case of COVID-19

The overall aim is to gain an understanding of the transmission dynamics of COVID-19 infection among cases and contacts within schools and other educational institutions.
Primary objectives are:

  • to estimate infection rates for overall and secondary COVID-19 infections in this context
  • to estimate the secondary clinical attack rate of COVID-19 in this setting
  • to estimate the fraction of asymptomatic COVID-19 infections within schools and other educational institutions
  • to describe the epidemiological and clinical characteristics of primary and secondary cases of COVID-19
  • to identify potential risk/protective factors associated with the COVID-19 infection risk.

Secondary objectives are:

  • to estimate the incubation period of COVID-19 and the duration of infectiousness and of detectable shedding;
  • to estimate the serial interval of COVID-19 infection in this setting;
  • to estimate the reproduction numbers: R0 and R of COVID-19 in this setting; and
    to characterize the serological response following confirmed COVID-19 infection

A prospective cohort study investigating maternal, pregnancy and neonatal outcomes for women and neonates infected with SARS-CoV-2

Question/ population:
pregnant or recently pregnant women (and their neonates), both infected with SARS-CoV-2 (exposed) and not infected with SARS-CoV-2 during pregnancy (unexposed).



Primary objectives:

  1. To analyze if SARS-CoV-2 infection in pregnant women increases the risk of adverse outcomes (as per outcomes 1-4 above) as compared to pregnant women who are not infected with SARS-CoV-2.
  2. To estimate the risk of mother-to-child-transmission of SARS-CoV-2 virus during pregnancy, intrapartum, postpartum (including during breastfeeding) among mother-neonate pairs with confirmed SARS-CoV-2 infection in pregnancy
  3. To describe viral presence and persistence in amniotic fluid, placenta, cord blood, fetus, neonate as well as in breast milk and other bodily fluids (urine, feces, vaginal fluids)
  4. To characterize the clinical course and disease spectrum of COVID-19 during pregnancy

Secondary objectives:

  1. Estimate the cumulative incidence of asymptomatic, subclinical, and clinically apparent SARS-CoV-2 infection during pregnancy, as assessed by seroconversion or a positive RT-PCR test during and following pregnancy.
  2. Measure the frequency of detectable RNA for SARS-CoV-2 by RT-PCR and IgG/IgM antibodies in neonates born to women infected with SARS-CoV-2 during pregnancy.
  3. Characterize the signs, symptoms, and disease course of neonates who have SARS-CoV-2 infection following childbirth from a pregnant woman infected with SARS-CoV-2

Optional secondary objective:

To determine if disease severity and disease characteristics of COVID-19 are different in pregnant women compared to non-pregnant women of reproductive age. 


Surface sampling of SARS-CoV-2: A practical “how to” protocol for health care and public health professionals

Question/ population:
For environmental surfaces

Primary objectives:

  • To assess the extent and persistence of surface contamination of SARS-CoV-2; and
  • To identify environmental surfaces and fomites that may play a role in onward transmission of COVID-19.

Secondary objectives such as, but not limited to:

To characterize of the sequence diversity of SARS-CoV-2 in environmental samples, as capacity and resources permit. 

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