CONTACT TRACING AND QUARANTINE IN THE CONTEXT OF THE OMICRON SARS-COV-2 VARIANT
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Contact tracing and quarantine in the context of
the Omicron SARS-CoV-2 variant
Interim guidance
17 February 2022
Key points
● This document provides updated guidance for contact tracing and quarantine of contacts in the context of
high levels of circulation of SARS-CoV-2, and in particular the variant of concern Omicron, which is currently
circulating at high levels and overwhelming health systems around the world.
● WHO continues to recommend using a risk-based, pragmatic approach for countries to consider when
introducing any changes to existing contact tracing and quarantine measures, taking into consideration the
continuity of the critical functions in society and the public health risks and benefits related to any change.
● Any interruption of contact tracing or shortening of the duration of quarantine will increase the risk of
onward transmission and must be weighed against healthcare capacity, population immunity and
socioeconomic priorities.
● Prioritization for identification and follow-up of contacts should continue to be given to contacts at highest
risk of getting infected or spreading the virus, those at highest risk of developing severe disease and health
and care workers.
● SARS-CoV-2 testing [PCR or antigen based rapid diagnostic tests (Ag-RDT)] can be used as a measure to
shorten quarantine, for example to seven days, if the contact shows no symptoms and presents a negative
test.
● Where testing to shorten quarantine is not possible, quarantine may be ended after day 10 without testing if
the contact presents no symptoms.
What is new
This document is an update of the Contact tracing1 and Quarantine2 interim guidance documents published in February
2021 and June 2021 respectively in the context of high levels of circulation of SARS-CoV-2, and in particular VOC
Omicron, which is overwhelming health systems around the world. This document should be read in conjunction with
the WHO interim guidance: Critical preparedness, readiness and response actions for COVID-193 and WHO interim
guidance: Recommendations for national SARS-CoV-2 testing strategies and diagnostic capacities.4
On 26 November 2021, WHO designated the variant B.1.1.529 a variant of concern (VOC) and named it “Omicron”.5
Based on currently available evidence, the overall risk related to Omicron remains very high. Omicron has a significant
growth advantage over Delta, leading to rapid spread in the community, with higher incidence than previously seen in
this pandemic. Despite a lower risk of severe disease and death following infection compared to Delta, the very high
levels of transmission have resulted nevertheless in significant increases in hospitalization, continue to pose
overwhelming demands on health care systems in most countries, and may lead to significant morbidity and mortality,
particularly in vulnerable populations. Given the high transmissibility of the Omicron variant, WHO is issuing an update
of its current Contact tracing and Quarantine interim guidance.1,2
WHO is providing public health authorities with this guidance on prioritizing contacts of COVID-19 cases in high
caseload situations to minimize extensive and high-risk transmissions. Another consideration is the possible shortening
of quarantine for contacts who test negative, do not develop symptoms and have recently received the primary series
or a booster dose of COVID-19 vaccine.
-1-Contact tracing and quarantine in the context of the Omicron SARS-CoV-2 variant: Interim guidance
Introduction
This document provides updated guidance on considerations to modify existing WHO contact tracing and quarantine
interim recommendations in the context of the COVID-19 pandemic.1,2 The considerations outlined in this interim
guidance take into account the intensity of SARS-CoV-2 spread in countries, local epidemiology and burden and
capacities of their health systems and other essential services.
As with previous periods of intense SARS-CoV-2 circulation, with the rapid spread of Omicron cases worldwide, contact
tracing capacities of many countries have been rapidly overstretched. The result has been prioritization of contact
tracing and quarantine efforts to target contacts in specific settings or contexts to minimize the risk of transmission of
the virus variant. Given this situation, countries may consider a pragmatic approach, considering that contact tracing
and quarantine requirements in the community may lead to significant disruptions of essential services, including
health services.
There is limited available scientific evidence on key epidemiologic parameters for the Omicron and how they impact
implementation of contact tracing and quarantine measures.6 WHO therefore continues to recommend adopting a
risk-based, pragmatic approach for countries to consider when introducing any changes to existing measures, taking
into account the continuity of the critical functions in society and public health risks and benefits in relation to the
pandemic.1,2
The risk-based approach should consider the local level of transmission, the severity of disease of circulating variants,
the levels of infection and vaccine-derived immunity, the capacity to track and trace contacts, access to rapid and
accurate SARS-CoV-2 testing, the capacity to assess the risk of exposures in health and care workers and other essential
services personnel and the health care systems’ capacities. Any interruption of contact tracing or shortening of the
duration of quarantine will increase the risk of onward transmission and must be weighed against healthcare capacity,
population immunity against Omicron and socioeconomic priorities.
The primary target audience of this interim guidance is the national public health authorities globally. However, other
users such as non-government organizations, research institutions and members of the public may also find the
guidance useful.
Current knowledge and uncertainties
Available evidence on Omicron does not change our current understanding of transmission of SARS-CoV-2.7 However,
when compared with the Delta variants, based on preliminary evidence, it appears to have a shorter serial interval
(2.2-3.5 days)8-10 and a shorter incubation period (2.9-3.2 days).9,11,12 Its secondary attack rate is higher13,14, and it has
demonstrated significant immune escape properties.11,14-16 Consequently, it is spreading more readily than previous
variants. Disease severity appears to be intrinsically lower than for previous variants12,17,18, further compounded by
more preserved vaccine effectiveness against severe disease than against infection. However, the large number of
cases that have occurred in a short time frame has nevertheless resulted in large numbers of hospitalized and critically
ill patients. Current evidence suggests that vaccine protection against infection and onward transmission for Omicron
infection is lower than for previous variants19-21, although vaccines (especially after booster dose) remain effective
against hospitalization and severe disease.6,22,23 However, data on vaccine effectiveness are limited, and only four
vaccines have been evaluated to date.6 Over time other more evaluations expected to occur and be published.
Prioritizing contacts to follow up
WHO recognizes that in situations where SARS-CoV-2 incidence is very high, it may not be possible to identify, monitor
and quarantine all contacts.3 In these situations it may not be practical or even possible for large numbers of contacts,
particularly health and care workers and other essential services personnel, be quarantined. These measures would
lead to a depletion of the workforce and disruption of health care delivery and societal functioning.
In situations where contact tracing capacity is overstretched, the aim may need to focus on reducing morbidity and
mortality rather than attempting to break all chains of transmission. In these situations, prioritization for contact
tracing should be given to:
-2-Contact tracing and quarantine in the context of the Omicron SARS-CoV-2 variant: Interim guidance
● contacts at highest risk of getting infected and those such as health and care workers who are at highest risk
of spreading the virus to vulnerable people, particularly those working in nursing homes, long-term care
facilities and hospitals; and other frontline essential workers
● contacts at highest risk for development of severe disease, such as people with comorbidities, the
immunosuppressed, the elderly and unvaccinated or under-vaccinated adults with no known prior SARS-CoV-
2 infection.
Contacts need to be identified, notified of their exposure and consulted on the potential risks. When it is impractical
to trace individual contacts, priority should be given to contact tracing in settings where the above high-priority
contacts are more likely to be found (e.g. long-term care settings). If notification of individual high-risk contacts by
health authorities is not possible, all cases, when aware of their status, should be encouraged to privately notify their
known contacts of their possible exposure, and public messaging by health authorities should provide guidance on
self-quarantine.
After the initial notification, where active follow-up is possible, it should be prioritized for contacts at high risk for
developing severe disease. Given the amount of work required for follow-up, remote technologies such as phone calls
or automated messaging with relevant information about testing and access to care in case of need should be put in
place for known high-risk contacts.
As per WHO guidance, if a contact develops symptoms, that individual should be considered as being suspected of
having COVID-19, and a referral pathway to testing should be available and recommended.4 In resource-constrained
settings and/or when testing capacity is limited and thus testing of all symptomatic contacts is not possible, highest-
risk contacts should be prioritized, as noted above.
Quarantine in a high COVID-19 incidence area
When COVID-19 incidence is high, e.g. situational levels 3 and 4,24 changes to the recommended duration of the
quarantine period (current WHO recommendation is 14 days1 for all contacts) may be considered. Risks and benefits
should be considered if any changes are being contemplated. Modelling and observational studies based on data for
previous SARS-CoV-2 VOCs have suggested that a SARS-CoV-2 diagnostic test can be added as criterion for exiting
quarantine earlier than 14 days while minimizing the possibility of onward spread of COVID-19.25-28 In these studies,
the models have shown that quarantine may be shortened, for example to seven days, if the contact has no symptoms
and presents a negative PCR or Ag-RDT, performed in an accredited laboratory or by a qualified professional, at the
end of the shortened quarantine period. Based on these studies, countries may consider shortening the quarantine
period to 7 days with the addition of a PCR or Ag-RDT administered by qualified personnel. WHO does not at this time
recommend self-administered tests to shorten quarantine.
Where testing to shorten quarantine is not possible, the absence of symptom development after a certain number of
days may be used as a proxy. For example, quarantine could be ended after day 10 without testing if the contact
presents no symptoms. The post-quarantine transmission risk for 10 days of quarantine (based on pre-Omicron data)
is estimated to be around 1%, with an upper limit of about 10%.25
If the quarantine period is shortened, WHO recommends individuals to continue to wear a well-fitted medical mask at
all times, during all indoor and outdoor activities where interaction with other people may occur, along with other
infection prevention and control (IPC) measures including physical distancing, appropriate ventilation of indoor spaces,
and hand hygiene, for the remainder of the total 14 days. These individuals should also continue to carefully self-
monitor for symptoms, and seek testing if symptoms arise.
Vaccinated contacts
Current data on vaccine effectiveness (VE) against Omicron are available from observational studies, most of which
are not yet peer reviewed, for four COVID-19 vaccines, and from five countries (Canada, Denmark, South Africa, the
United Kingdom of Great Britain and Northern Ireland and the United States of America.15,16,19,21,23,29-37 As of 7 February
2022, results from studies evaluating VE consistently show limited VE against Omicron infection or symptomatic
disease after the primary series, and a higher VE against infection following boosting.6,38 The vaccine-induced
neutralizing antibodies immune response has been shown to wane over time, although cellular immunity appears
-3-Contact tracing and quarantine in the context of the Omicron SARS-CoV-2 variant: Interim guidance
more long-lasting; currently no clear threshold of any biological indicator is available to use as a correlate of
protection.6,39
Within 90 days after the primary series or booster vaccination, there is evidence that vaccination can reduce the
likelihood of infection with Omicron.14,30,35,40 Thus, where active follow-up of individual contacts is possible, recently
vaccinated contacts can be considered as lower priority for contact tracing or undergo shorter quarantine as outlined
above, where resources are limited and/or health systems are overstretched. Beyond approximately 90 days, due to
waning protection against infection after the primary series and limited follow-up data for booster doses, vaccinated
contacts should be considered the same as unvaccinated contacts.
Reinfection
Individuals previously infected with pre-Omicron variants are at risk for infection with Omicron, although there
appears to be reduced risk as compared to those without prior infection.41 Although two consecutive infections with
Omicron have not been reported so far, it is expected that reinfection with Omicron would be possible after a period
of immune waning or, for example, if there are differences in the immune escape potential of Omicron sub-lineages
(e.g. BA.1 versus BA.2).42 Thus, contacts who have been infected in a context where Omicron is the dominant variant
(i.e. whose infection was likely caused by Omicron) could quarantine for a shorter period, as they could be considered
a lower priority in settings where contact tracing and quarantine capacities are stretched. There is as yet no evidence
on the specific duration of infection-derived immunity against Omicron, but based on prior variants, immunity is
expected to persist at least 90 days43, so this conservative estimate could be applied. Individuals whose prior confirmed
SARS-CoV-2 infection (regardless of the variant) is more distant should be treated the same as contacts with no known
history of infection.
Considerations for health and care workers
WHO continues to advise that health workers who have had high risk of SARS-CoV-2 exposure should refrain from
work and follow quarantine policies to avoid risking exposure to patients, colleagues, their families and contacts in the
community.43-45 However, in the context of widespread community transmission of SARS-CoV-2 (any variant), the
incidence of health worker infections may rise from higher amounts of exposure in the workplace and the community,
resulting in reduced capacity to respond to case surges and maintain essential health services.3 Consequently, the
considerations and strategies proposed above regarding quarantine in a high caseload environment are particularly
relevant for health workers.
Based on these considerations, quarantine may be shortened to seven days for an exposed health worker who is
asymptomatic and tests negative (either by RT-PCR or Ag-RDT) on day 7 following exposure, or to 10 days following
exposure without testing. In addition, vaccination status and previous COVID-19 could be considered when setting
policies for modifying quarantine criteria for health workers. In particular, when the health system is under extreme
pressure because of a high caseload and when many health workers are off work due to exposures or infections, health
workers who have had high-risk exposure but have received a vaccination booster or recovered from SARS-CoV-2
infection within 90 days30,35,40 may continue to work with no quarantine if they are asymptomatic. Ideally, frequent
testing with an Ag-RDT should be performed up to day 14 after exposure.44
Health workers with shortened quarantine or who are continuing to work following high-risk exposure must continue
to follow all recommended infection IPC precautions, including continuously wearing either a well-fitted medical mask
or a respirator at all times46, self-monitoring for symptoms and getting tested, if possible. Ideally and if compatible
with service delivery needs, these health workers should not provide care or have contacts with immunosuppressed
patients or other high-risk patients (e.g. those with co-morbidities or who are elderly).
Regardless of the intensity of SARS-CoV-2 incidence, it is critical that national authorities and health facilities continue
to strengthen IPC measures in all settings, including having an IPC programme or at least a dedicated and trained IPC
focal point in place. Also crucial are engineering, environmental and administrative controls, standard and
transmission based -precautions, screening and triage for early identification of cases and source control and COVID-
19 surveillance and vaccination of health workers. The rapid spread of Omicron and high proportion of individuals who
may be infected but are asymptomatic make these measures more important than ever.
-4-Contact tracing and quarantine in the context of the Omicron SARS-CoV-2 variant: Interim guidance
Process and methodology
This interim guidance was developed based on available evidence on the Omicron variant current at the time of
development of this guidance. A small group of WHO experts with relevant background and expertise undertook a
rapid review of evidence on the Omicron variant. The search for the rapid review was conducted on the WHO COVID-
19 Global literature database47, which includes peer reviewed publications, pre-print articles and grey literature
sources, complemented by manual searching of additional grey literature. All publications reporting studies with
original data on Omicron transmission dynamics were included, and their data were extracted and compiled in a
tabular format. The information was then grouped based on main transmission indicators and synthesized. After
collection and synthesis of the evidence, the group undertook a series of consultations with internal and external
technical experts including the members of the WHO Health Emergencies Programme (WHE) Contact Tracing and
Quarantine Guidelines Development Group (CT-GDG) and the COVID-19 Infection Prevention and Control (IPC)
Guidelines Development Group. Where evidence was scarce, or in situations where the evidence was unclear, WHO
sought expert opinions of GDG members and senior WHO technical staff members. Any decisions based on evidence
were reached through consensus among GDG members. In addition to the modelling and observational studies
referenced, evidence emerging from the practice of countries that implemented shorter quarantine rules earlier were
shared and discussed.
The proposed changes are justified from published and observed evidence, as well as the need for pragmatic risk-
based decisions needed to address the burden put on societies and healthcare systems by the high number of Omicron
cases.
Plans for updating
This interim guidance is specific to the present global surge of cases due to the SARS-CoV-2 Omicron variant and is
meant to be read in conjunction with the current WHO guidance on contact tracing and quarantine. A consolidated
contact tracing and quarantine guidance with updated evidence is currently under development, which, when ready,
will replace both this as well as the current contact tracing and quarantine guidance documents. Furthermore, the
update of the WHO guidance on Prevention, identification and management of health worker infection in the context
of COVID-19 is also under way and will provide more details on evidence and guidance on this topic, and when ready,
will replace the current document.
Acknowledgement
WHO gratefully acknowledges the technical inputs and expert advice provided by the members of the Contact Tracing
and Quarantine Guidelines Development Group (GDG) and the Infection Prevention and Control GDG.
Declaration of interests
Declarations of interests were collected from all external contributors and assessed for conflicts of interest. There
were no significant conflicts of interest declared by the external contributions to this guidance.
Funder
Funded by WHO.
-5-Contact tracing and quarantine in the context of the Omicron SARS-CoV-2 variant: Interim guidance
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