key: cord-0897167-hreykuox authors: Ingham, G.; Kippen, R. title: Should I stay or should I go? Observation post-vaccination during the COVID-19 pandemic and the law of unintended consequences date: 2022-04-12 journal: nan DOI: 10.1101/2022.04.05.22273373 sha: f0792823c1f0d69da4a448491664e5b7e5649e9c doc_id: 897167 cord_uid: hreykuox Background Standard practice after all vaccinations in Australia is to observe patients for 15 minutes. During the COVID-19 pandemic, could the risk of contracting and dying from COVID-19 acquired in the waiting room be greater than the risk of dying from post-vaccine anaphylaxis when leaving immediately? Methods The risks are modelled for a patient aged 70+ years attending for annual influenza vaccination in a typical Australian general practice clinic. The risk of death from anaphylaxis is estimated based on known rates of anaphylaxis shortly after influenza vaccination. The risk of acquiring COVID-19 during a 15-minute wait and then dying from that infection is estimated using the COVID-19 Aerosol Transmission Estimator and COVID-19 Risk Calculator. Results Other than at times of extremely low COVID-19 prevalence, the risk of death from anaphylaxis for a patient aged 70+ years leaving immediately after influenza vaccine is less than the risk of death from COVID-19 acquired via aerosol transmission during a 15-minute wait. The risk of death from COVID-19 is greatest for the unimmunised and when masks are not worn. Conclusions A more nuanced approach to advice post-vaccination is recommended that considers current COVID-19 prevalence and virulence, the characteristics of the waiting room, the risk of anaphylaxis, and the patients susceptibility to death from COVID-19. There are many circumstances where it would be safer for a patient to leave immediately after vaccination . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 12, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 NOTE: This preprint reports new research that has not been certified by peer review and should not be used to guide clinical practice. " I f I g o t h e r e w i l l b e t r o u b l e . A n d i f I s t a y i t w i l l b e d o u b l e " T h e C l a s h Abstract: Background: Standard practice after all vaccinations in Australia is to observe patients for 15 minutes. During the COVID-19 pandemic, could the risk of contracting and dying from COVID-19 acquired in the waiting room be greater than the risk of dying from post-vaccine anaphylaxis when leaving immediately? Methods: The risks are modelled for a patient aged 70+ years attending for annual influenza vaccination in a typical Australian general practice clinic. The risk of death from anaphylaxis is estimated based on known rates of anaphylaxis shortly after influenza vaccination. The risk of acquiring COVID-19 during a 15-minute wait and then dying from that infection is estimated using the COVID-19 Aerosol Transmission Estimator and COVID-19 Risk Calculator. Results: Other than at times of extremely low COVID-19 prevalence, the risk of death from anaphylaxis for a patient aged 70+ years leaving immediately after influenza vaccine is less than the risk of death from COVID-19 acquired via aerosol transmission during a 15-minute wait. The risk of death from COVID-19 is greatest for the unimmunised and when masks are not worn. Conclusions: A more nuanced approach to advice post-vaccination is recommended that considers current COVID-19 prevalence and virulence, the characteristics of the waiting room, the risk of anaphylaxis, and the patient's susceptibility to death from COVID-19. There are many circumstances where it would be safer for a patient to leave immediately after vaccination. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted April 12, 2022. Should I stay or should I go? Observation post-vaccination during the COVID-19 pandemic and the law of unintended consequences Introduction Short-term (15-minute) observation after vaccination is standard clinical practice for all vaccines administered in Australia. This enables prompt management of immediate adverse reactions, particularly anaphylaxis, to reduce the risk of hospitalisation and death (Australian Technical Advisory Group on Immunisation 2018b). Prior to winter, adults aged 65+ years are strongly recommended to receive an influenza vaccine (Australian Technical Advisory Group on Immunisation 2018a). This year (2022) the incidence of COVID-19 infections is high and expected to increase coming into winter (Clun 2022 ). There is a risk of acquiring COVID-19 infection while waiting in a shared waiting room after influenza vaccination. For patients attending for their annual influenza vaccine, will the risk of death from contracting COVID-19 in the waiting area be greater than the risk of death from anaphylaxis? In what circumstances should the current after-care advice be changed to instead instruct patients to leave immediately after their influenza vaccination? In this paper we explore these questions by modelling the risks for patients aged 70+ years attending a typical general practice for their annual influenza vaccine. We estimate the increased risk of death from anaphylaxis were patients to leave immediately after vaccination versus the increased risk of contracting COVID-19 in the waiting room, and the subsequent risk of dying from it. We model different scenarios considering the impact of the background rate of COVID-19 in the community, patients' COVID-19 vaccination status, and whether those present are wearing masks. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 12, 2022. ; https://doi.org/10.1101 /2022 .04.05.22273373 doi: medRxiv preprint (McNeil et al. 2016 . It is likely that patients with reactions within 1-2 minutes of vaccination will still be identified and treated, and many who suffer anaphylaxis after leaving the clinic will be able return in time to obtain medical care. In estimating the increased risk of death from anaphylaxis if patients leave immediately post-vaccination rather than waiting 15 minutes, we hypothesise that half of the patients experiencing anaphylaxis in the first 30 minutes will die resulting in 0.3 deaths per million influenza (Riley et al. 1978; Riley 2001) . In the COVID-19 Aerosol Transmission Estimator, empirical data from known and well-documented COVID-19 transmission events has been used to determine the amount, or 'quanta', of aerosolised COVID-19 virus required to cause infection. In other words, the COVID-19 Aerosol Transmission Estimator is a model that has been calibrated using real world data. Full details of the assumptions used in our calculations are available in Appendix 1. In brief, our typical general practice waiting room 'box' was developed by first adopting the recommended waiting room design of 6 waiting room chairs per general practitioner (GP) and 2 metres 2 per chair = 12m 2 per GP (Royal Australian College of General Practitioners 2012). Two-thirds of GPs in Australia work in a group practice of 3-10 doctors (Royal Australian College of General Practitioners 2021). We selected 6 doctors as a midway figure, resulting in a waiting room area of 72m 2 . We assumed 2.4 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 12, 2022. months of the third vaccine, 40% at 4-6 months after the third vaccine, and only 5% more than 6 months after the second vaccine (UK Health Security Agency 2022). We have therefore selected for our model the fraction of the population immune from infection (not immunity from severe disease or death) as 50%. There may be future scenarios with new COVID variants where population immunity to infection is lower than 50%. For the influenza immunisation clinic for patients aged 70+ years, two models were created for 6 vaccinators operating with 5-minute appointments. The first model represents current clinical practice of 20 minutes in total in the waiting room, 5 minutes before and 15 minutes after vaccination, with an average of 24 people present. The second model represents altered practice, with 6 patients waiting 5 minutes before the appointment and then leaving immediately after vaccination. The increased risk of contracting COVID-19 with a 15-minute wait post-vaccination (versus no wait postvaccination) is estimated as the net difference of risk between the two models. It is not possible to predict either the prevalence of COVID-19 disease in the community or government policy regarding mask requirements at the time of influenza vaccinations this year (2022). To account for this uncertainty, we ran our models for . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 12, 2022. ; https://doi.org/10.1101/2022.04.05.22273373 doi: medRxiv preprint different rates of COVID-19 infectivity prevalence in the community (1%, 0.5%, 0.1%, 0.025%) and for those in the waiting room either all wearing masks or all not wearing masks. The outcomes for the eight modelled scenarios are shown in Figure 1 . The risk of contracting COVID-19 varies from a high of 3.31 cases per 1,000 15-minute 'waits' (for community infectivity prevalence of 1% and everyone unmasked) to a low of 0.02 per 1,000 (for prevalence of 0.025% and everyone masked). If an infection is contracted in the waiting room, the risk of dying (the case fatality rate) When should a patient aged 70+ years be advised to leave immediately after influenza vaccination? The combined risk of a patient aged 70+ years contracting COVID-19 during a 15minute wait post-vaccination and subsequently dying from the infection is displayed in Table 1 under different scenarios, calculated by multiplying the rates in Figure 1 by the rates in Figure 2 . Scenarios is which it would be safer to leave (risk of anaphylaxis of 0.3 per million is less than the risk of contracting and dying from COVID-19) are unshaded. When community COVID-19 infectivity prevalence is 0.5% (1 in 200) or greater, it is safer for all those aged 70+ years to leave immediately after influenza vaccination, no matter their COVID-19 vaccination status, or whether masked or unmasked. This is because the risk of contracting COVID-19 in the 15-minute wait and dying from that infection is greater than 0.3 per million and thus outweighs the risk of anaphylaxis from influenza vaccine within those 15 minutes. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 12, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 At the other end of the scale, if community COVID-19 infectivity prevalence is extremely low -0.025%, or 1 in 4,000 -then it is safer for most people aged 70+ years to stay for 15 minutes after influenza vaccination (COVID-19 risk is equal or lower than anaphylaxis risk), but only if they are immunised. Even then, failure to wear a mask would render those with sub-optimal immunisation status unsafe. Vaccination in Australia occurs in a wide variety of settings, from small pharmacies through to drive-through clinics. We modelled an intermediate risk setting -a mediumsized general practice. Our model has not included risk factors other than age, immunisation status, mask wearing, and background community infectivity prevalence. The risk of death from anaphylaxis if leaving earlier than 15 minutes will be greater for those with a history of anaphylaxis. The risk of death from COVID-19 acquired waiting 15 minutes longer in the waiting room will be higher for those with comorbidities like diabetes or asthma. In determining whether to advise a patient to stay or go after a vaccination, a clinician needs to consider the risk of death from anaphylaxis from that vaccine were the patient . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 12, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 to leave, the risk of death were they to contract COVID-19, and the risk of acquiring COVID-19 at that time and in their waiting room. In April 2020, at the commencement of the COVID-19 pandemic, when droplet spread was considered the major mode of COVID-19 transmission and prior to the availability of COVID-19 immunisations, the Australian Technical Advisory Group on Immunisation (ATAGI) advised only 5-minutes observation was required after vaccination if physical distancing could not be achieved in the waiting room (Australian Technical Advisory Group on Immunisation 2020). Our model included physical distancing of at least 1.5 metres in the waiting room (1 patient per 3m 2 ) and excluded the risk of droplet and fomite spread. Our findings indicate that there are circumstances where aerosol transmission alone is enough to advise against the patient remaining in the waiting room. We propose that more nuanced advice that considers changing COVID-19 prevalence and virulence be given to vaccination providers about vaccination after-care. Patients with a history of anaphylaxis may be safer to be observed after vaccination, but elderly and particularly unimmunised patients should be instructed to leave unless the background infectivity rate of COVID-19 is very low. Patients should continue to wear masks when attending indoor vaccination clinics and physical distancing should be maintained. From a public health perspective our example illustrates the operation of what has been termed the 'law of unintended consequences'. Policies may be designed with good intention-in this case to ensure prompt management of anaphylaxis-but may unintentionally have adverse outcomes that outweigh any benefit (Newman et al. 2003; Turcotte-Tremblay et al. 2021) . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 12, 2022. ; https://doi.org/10.1101 https://doi.org/10. /2022 Calculations are based on the assumptions in Appendix 1 inputted to the COVID-19 Aerosol Transmission Estimator (Jimenez and Peng 2022) . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 12, 2022. ; https://doi.org/10.1101/2022.04.05.22273373 doi: medRxiv preprint CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The copyright holder for this preprint this version posted April 12, 2022. Calculated by multiplying the rates in Figures 1 and 2 . Shaded in grey are scenarios under which the risk of contracting COVID-19 within the 15-minute wait, and dying from that infection, are less than or equal to the risk . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted April 12, 2022. ; https://doi.org/10.1101/2022.04.05.22273373 doi: medRxiv preprint of anaphylaxis within the 15-minute wait (0.3 per million). Under these shaded scenarios, it is as safe or safer to wait for 15 minutes. Under the unshaded scenarios, it is safer to leave immediately after vaccination. AZ=AstraZeneca COVID-19 vaccine; Pfz=Pfizer COVID-19 vaccine; booster=third dose of either Pfizer or Moderna COVID-19 vaccine The data that support this study are available in the article and accompanying online supplementary material. . 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