CME INDIA Presentation by Dr. Rajeev Jayadevan, MD DNB MRCP ABIM (Med/GE) Co-Chairman National IMA COVID Task Force. (Special thanks to Dr. Ramesh Shenoy and Ms Anithadevi TS, our statistician for the success of the survey).
The high breakthrough infection rate implies that vaccination as a standalone strategy will not be enough in the days to come. Multiple strategies of protection will likely be required long-term from a public health perspective.
What is this Study?
- Dr. Rajeev J group had previously published about the safety of vaccination in India in February 2021.
- Now they have presented latest study results about 3rd wave in India. Input was received and analysed from nearly 6000 people of diverse backgrounds and age groups.
- This study shines light at multiple areas that were previously unknown, or unpublished. It will therefore serve to bridge several knowledge gaps.
- The third wave of the pandemic in India lasted from January till March 2022, and breakthrough infections were common.
- Third dose of vaccine was rolled out to priority groups in the beginning of 2022. There is no published information available about the clinical outcomes in this context
- Why this study was planned
- To assess the community level experience of the pandemic, with focus on the third wave and vaccination in India.
- To describe the experience of the boosted and non-boosted population during 3rd wave.
- To study the public perception about the precautionary (3rd) dose in India.
- What was found?
- Among 5971 respondents, 98.6% were vaccinated, 40% of whom had also received the 3rd dose.
- Age range: 24% were below 40, 50% were 40-59, 26% were >60 years. 45% were women, 53% were healthcare workers.
- COVID-19 was reported by 3361 (56%) respondents. Among those who reported COVID-19, 2311 (70%) were infected during the third wave.
- Severe symptoms occurred in <1%, while moderate severity was reported by 42%.
- Repeated bouts of infection were common; 15% of those with history of COVID-19 had been infected at least twice. 44% of the respondents (2610/5971) did not report a history of COVID-19.
- The third dose was taken by 2383 individuals, of whom 30% reported COVID-19 during the 3rd wave.
- The boosted group also had higher N95 use, and a greater proportion of healthcare workers. Among those who did not take a 3rd dose, 45% reported COVID-19 in the 3rd wave.
- COVID-19 incidence was lower at 27% among those in this group who had recently received their second dose. Longer gap after the second dose correlated with higher chance of infection during 3rd wave.
- Giving a 3rd dose before a 6-month gap since the second dose did not make a difference in infection rate.
- Covaxin and Covishield recipients had the same incidence of COVID-19 during the third wave. While 35% of the respondents believed it was helpful, 65% of the respondents were either uncertain or disapproving of the benefit of a 3rd dose.
- What this study adds
|1. 30% of respondents who received a 3rd dose went on to get COVID-19 during the 3rd wave.|
|2. Younger adults were more likely to be affected during 3rd wave.|
|3. Although severe disease was rare, 42% reported having symptoms of moderate severity that could temporarily incapacitate people, affecting their routine and productivity.|
|4. The proportion of different grades of severity was similar among all vaccinated people, regardless of whether they received a 3rd dose.|
|5. Reinfections occurred in 15%, and were not always milder.|
|6. Among those who did not receive a 3rd dose, 45% reported COVID-19 in the 3rd wave. However, this group had lower use of N95 masks (50%) than the 3rd dose group (68%) which may have reduced the overall protection.|
|7. The longer the gap after second dose, the greater was the chance of reporting COVID-19. 8. People who received their second dose recently had the same incidence of third wave COVID-19 as following a 3rd dose.|
|9. 3rd. dose, given too close to the second dose made no difference in the infection rate.|
|10. Covaxin and Covishield recipients had the same rate of COVID-19 in the third wave.|
|11. Although the respondents were 98.6% vaccinated at baseline, there was considerable uncertainty (65%) amongst them about the benefit of a 3rd dose.|
- The third wave of the pandemic arrived in India in late December 2021 and subsided by March 2022. Unlike during the delta wave in 2021, this time the virus was met by a largely vaccinated adult population: most adults had received either Covishield (adenovirus vector) or Covaxin (inactivated virus).
- In addition, many individuals had already acquired immunity through natural infection. In India, 3rd dose of the same vaccine (technically a homologous booster dose) was authorized for healthcare and frontline workers and for people over the age of 60, on January 10, 2022.
- Both these vaccines are known to generate an immune response when used as a homologous booster dose (1,2). However, there is no published information available on the clinical outcomes of this intervention in the Indian context.
- With more waves expected in the future, and wider availability of 3rd doses now to all above the age of 18, it is important to collect pertinent information about the overall community experience during the third wave.
- The survey was therefore done as the Omicron-driven third wave was winding down in India, after sufficient time had elapsed for the 3rd dose to take effect among recipients.
- At the time of completion of the study, 20 million precautionary (booster) doses had already been administered, while 96.4% adults had received at least one dose and 82% had received two doses (3).
For ease of discussion, the term 3rd dose will henceforth be used instead of precautionary dose
- To understand the 3rd wave experience at the community level, with regard to infection rate, severity, vaccination status, gap since vaccine dose and 3rd. dose uptake.
- To describe the experience of the boosted and non-boosted population during 3rd wave.
- To study the public perception about 3rd dose vaccination.
- A cross-sectional online survey was performed from 15 February till 10 March 2022, which included questions pertaining to 3rd wave experience in India.
- The survey was sent for the attention of all adults based in India who may or may not have had a history of COVID-19.
- Questions were formatted in a clear and binary fashion and were validated before the wide launch through email and social media platforms. For instance, to classify people according to disease severity, as a direct interview was not possible, we carefully constructed a simple-to-use multiple-choice question that had discriminatory power (3).
- Details are given in figure 12.
- The questionnaire was kept as short and easy as possible to achieve the balance of generating pertinent unambiguous data, while enhancing survey referrals through a positive user experience. Incomplete responses could not be submitted. Only one response was possible from a single user. The response was enthusiastic, with 5971 adults completing the survey. Provision was provided to add descriptive comments if the respondent felt the need to. This section also received considerable response, with as many as 795 people sending their comments.
- The percentage of vaccinated respondents (98.6%) in the survey closely matched that of vaccinated adults in India at that time (96.4%). There was no clustering of unusual responses, indicating that the participation was legitimate and balanced, from individuals of varied demographic background across the country rather than focused groups of people. The data presented in the study were exclusively obtained through the online survey.
- Descriptive statistics was used to present all outcomes. Binary and categorical variables were presented using counts and percentages. For the comparison of categorical variables, either chi square or fishers exact test were used. All the data were entered in Microsoft excel and analysed using SPSS version 20.00.
- Profile of respondents
- The survey was completed by 5971 adults based in India, 56% of whom reported a history of COVID19. A substantial number (3180, 53%) worked in healthcare.
- Women comprised 45% of respondents.
- There was a wide range of age distribution; 50% belonged to the age group of 40-59, 24% were below 40, while 26% were 60 and above.
- Among the 5971 survey respondents, the third dose was taken by 2383 individuals, of whom 1701 (71%) were healthcare workers.
- Incidence of COVID-19 among respondents
- 39% (2311/5971) were infected during the third wave, while 18% (1050/5971) were infected during previous waves.
- Younger age groups were more likely to report COVID-19 during the 3rd wave (see figure 2). 44% of the respondents (2610/5971) did not report a history of COVID-19
Table 1: Demographic profile of the survey respondents
Figure 2: The percentage of people in each age group who were affected by the 3rd wave
- Severity of the third wave
- Among the 2311 who were infected during the third wave, 4.8% were asymptomatic while 53% had mild symptoms. Moderate severity was reported by 41.5%, while 0.69% had severe COVID-19.
- Figure 3: Symptom severity profile of 3rd wave in India
- Number of times infected
- COVID-19 2868/3361 (85%) were infected only once. 454 (14%) had it twice. 26 people (0.8%) reported being infected 3 times. Two people reported being infected four times, while 12 (0.4%) said they had COVID-19 five times.
- Figure 4: Number of times a person was infected
5. Profile of vaccine use
- 86.4% (5157) used Covishield
- 8.8% (523) took Covaxin
- 0.3% (20) Sputnik V
- 3.1% (188) took others.
- 1.4% (83) were unvaccinated.
6. 3rd wave infection pattern across vaccines, used as primary series
- Among 5157 people who took it, 2010 (39%) reported COVID-19 during 3rd wave
- 2. Covaxin
- Among 523 people who took it, 210 (40%) reported COVID-19 during 3rd wave
Figure 5: Percentage of vaccine primary series recipients who turned positive during the 3rd wave
7. 3rd wave infection pattern by vaccines, used as 3rd dose
- 646 (30.2%) were infected out of 2140 who took Covishield 3rd dose
- 38 (30.1%) were infected out of 126 who took Covaxin 3rd dose
- 32 (29%) were infected out of 109 among other types of vaccine
Figure 6: Percentage of 3rd dose vaccine recipients who turned positive in 3rd wave
8. 3rd. dose uptake among respondents
- 2383 out of 5971 (40%) respondents took 3rd dose
9. 3rd dose uptake among healthcare workers
- 1701/3180 (53.5%) took 3rd dose Healthcare workers were more likely to receive 3rd dose. This was expected because of the prioritisation during 3rd rollout.
10. 3rd dose uptake among non-healthcare workers
- 682/2791 (24.4%) took 3rd dose
11. 3rd wave positive rates among those who got 3rd dose, versus those who did not take 3rd dose
- Of the 2383 people who took 3rd dose, 716 (30%) reported positive during 3rd wave
- Among 3505 vaccinated people who did not take it, 1577 (45%) reported positive during 3rd wave
Figure 7A: Third wave positivity according to whether 3rd dose was taken or not
Figure 7B: Comparison of confounding factors that could have affected the outcomes of 3rd dose
12. 3rd. wave COVID-19 incidence, based on the time gap since 2nd dose
- Analysis based on gap since 2nd dose alone (some have taken 3rd dose)
- Among the recently vaccinated group (<1 month ago) only 27% (59/221) were positive in the 3-rd. wave.
- Among the intermediate group, 38% (377/995) were positive in the 3rd wave.
- Among the recently vaccinated group (> 6 month-gap group, 40% (1719/4267) were positive in the 3rd wave.
- Analysis after excluding those who also took the 3rd dose from the above group:
- Among the recently vaccinated group (<1 month ago) only only 27% (23/86) were positive in the 3rd. wave
- Among the intermediate group, 37.3% (474/1270) were positive in the 3rd wave
- Among the recently vaccinated group (> 6 month-gap group, 49% (1147/2350) were positive in the 3rd wave
This indicates that infection was more common among those who had longer gap after 2nd dose. In other words, protection from infection appeared to be linked with how recent the last vaccine dose was.
Figure 8 A: 3rd wave positivity according to gap since receiving 2nd dose, among those who did not take 3rd dose
13. 3rd. dose outcome, based on gap since 2nd dose
We looked at people who took the third dose after varying gaps from the second dose. They were categorized into three groups:
- Recent: those who took 3rd dose within 1 month of their second dose.
- Intermediate: 3rd dose taken after 2-5 months gap.
- Late: 3rd dose taken >6 months after 2nd dose.
In these three groups, we assessed the impact of the 3rd dose, as measured by the difference in 3rd. wave positivity rates. We found that a 3rd dose given early or during intermediate period made no difference to the baseline infection rate. But when the gap was >6 months after the second dose, taking a 3rd dose generated a 19% lower incidence of COVID-19 in the 3rd wave.
Figure 8 B: Difference in percentage of infection rates between 3 and 2 dose groups, classified on the basis of gap between 2nd and 3rd doses. The longer the gap, the greater the additional protection observed.
14. 3rd. wave infections after sufficient time elapsed since 3rd dose
- Of the 716, only 667 provided complete information on timing
- Among 667 cases who had 3rd dose breakthrough infection (that is, COVID-19 occurring in spite of taking a 3rd dose), 516 (77%) got infected at least 2 weeks after the third dose.
15. Severity of 3rd wave breakthrough infections
Among those who had a 3rd dose, 716 got infected during 3rd wave
- Asymptomatic 3%
- Mild 58.5%
- Moderate 37%
- Severe 0.3%
Among those who were vaccinated, but did not receive 3rd dose, 1577 got infected during 3rd wave
- Asymptomatic 5%
- Mild 50.8%
- Moderate 43.4%
- Severe 0.76%
Figure 9: 3 rd. wave symptom severity profile classified according to whether 3rd dose was taken or not
The severity profile of 3rd wave symptoms among vaccinated people who took 3rd dose and those who did not, were similar. The minor differences shown in the graph were not significant.
Figure 10: Age of those who suffered moderate severity of COVID-19 during 3rd wave, expressed as % of total respondents. Although the chance of testing positive has higher among
Table 2: 3rd wave positivity by vaccine type, 3 rd. dose, timing of 2nd dose, public opinion about precautionary dose
16. Public opinion: “Do you think a precautionary dose is helpful?”
- Overall, 2104/5971(35.2%) believed it is helpful
- 3347 (56%) were unsure
- 520 (8.7%) did not think it was helpful
Figure 11: Public opinion about precautionary dose
17. Opinion among those 2311 infected in 3rd wave
- 29% said helpful (671/2311)
- 58% were not sure (1345/2311)
- 12.7% said not helpful (295/2311)
18. Opinion among those 3660 who were not infected in 3rd wave
- 39% said helpful (1433/3660)
- 55% were not sure (2002/3660)
- 6.1% said not helpful (225/3660)
Figure 12: Sample of questions sent to assess severity of COVID-19 among respondents
For question no.2, more than one of the six choices could be selected, depending on individual severity.
They were later classified as asymptomatic, mild, moderate and severe.
- Asymptomatic: option 1
- Mild: option 2
- Moderate: options 3 or 4, but not 5
- Severe: must include option 5 Those who were not infected could choose option 6
Figure 13: Vaccination status on March 8, 2022, by Press Information Bureau of India
- The highlight of this cross-sectional survey was that 30% of those who took the third dose, reported COVID-19 afterwards during the third wave.
- The high breakthrough infection rate following the 3rd dose is remarkable because it occurred during the early period, where booster protection is expected to be maximum. This is consistent with reports elsewhere about Omicron being able to infect up to 64% of individuals who had recently received a 3rd. dose booster of mRNA vaccine (4).
- We found that among the individuals who got 3rd dose breakthrough infection, 77% got infected after sufficient time had passed after receiving the dose for antibody levels to be boosted (2 weeks or more). In other words, the high rate of infection observed was not because the 3rd dose was taken too close to the third wave.
- The survey indicates that despite high baseline rate of vaccination among the respondents (98.6%), more people were affected in the 3rd wave than during the initial two years, as reported elsewhere. (5)
- Among those infected during the 3rd wave, symptoms of moderate severity were reported by 41.5%. This shows not only the immune escape potential and transmissibility, but also the considerable morbidity and loss of productivity caused by Omicron.
- For the purpose of classification, moderate disease included positive answers to the questions
- needed bed rest and/or
- hospitalisation with no oxygen required.
Less than 1% of those affected in the 3rd wave reported severe disease, defined as those who required supplemental oxygen during hospitalisation (6).
- The percentage of severe disease during the 3 rd wave remained below 1% among all vaccinated individuals, whether they received the 3rd dose or not. The reported percentage of severe infections was only 0.6% in the 3rd wave. It is noteworthy that 15% (3/20) of the severe cases were reinfections, and occurred among vaccinated individuals. This disproves the popular notion that that reinfections are always milder than the first episode.
- Younger adults < 40 years of age had the highest positivity rate (Table 1, Figure 2). This was similar to the Omicron experience in South Africa (7) and could explain the relatively low severity observed. Given equal baseline vaccination coverage among the respondents, reasons for this age gradient during the 3rd wave could be greater mobility and social mingling among younger adults, and additional precautionary measures taken by older individuals.
- The reported 3rd wave infection rate among those who did not take the 3rd dose was higher at 44.5%. The trend suggests that infection rate was lower among those who took the third dose (Figure 7a). At the same time, those who did not take the 3rd dose had a similar overall severity profile to those who took the 3rd dose. (Figure 9)
- Although it is conceivable that the reduced infection rate was due to the effect of the 3rd dose, it is noteworthy that the 3rd dose uptake among healthcare workers (53.5%) was more than double that of those of non-healthcare background (24.4%).
- Among healthcare workers, factors such as superior mask use, knowledge and adherence to airborne infection preventive measures, and the downstream effects of prior exposure could have also reduced the rate of infection. For instance, healthcare workers in our survey were more likely to wear an N95 mask (78%) compared to non-healthcare (46%). Accordingly, we found that the 3rd dose group had significantly higher use of N95 masks (68%) than those who did not take 3rd dose (50%), p < 0.001. The 3rd dose group also had higher percentage of healthcare workers (73%) compared to the non-boosted group (40%), p <0.0001(Figure 7b)
- Testing rates could be lower among people who took the 3rd dose due to greater confidence levels. Thus, asymptomatic or mildly symptomatic cases could have been missed. In other words, those who received the 3rd dose had other protective factors too working in their favour. Unlike a randomised trial or test-negative case-control study where such confounders can be controlled for, a survey is not a suitable tool to directly compare incidence rates, particularly between dissimilar groups of respondents. In response to the question about whether they felt the precautionary dose was helpful, only 35% felt it was helpful, 9% believed it was not helpful, while 56% were unsure. That two-thirds of the respondents were either unsure or disapproving of the 3rd dose is a significant observation, considering this group has a 98.6% vaccine acceptance rate prior. Those who were infected during the third wave despite the 3rd dose had lower confidence in the 3rd dose, only 29% believed it was helpful. The continued trust was because some of them believed the 3 rd dose made their disease milder.
- The following where the main reasons people gave for taking the 3rd dose:
- ‘vaccine boosts immunity’
- ‘vaccine made disease milder’
- ‘vaccine had previously helped prevent infection in spite of known exposure’.
The chief reason that people mentioned for not taking the 3rd dose was that infections were being commonly reported after third dose.
- Several respondents also shared their personal experience of getting infected despite 3rd dose. Other stated reasons for not taking 3rd dose were: 1) belief that prior infection would be protective 2) ‘lack of enough evidence’ 5) adverse experience with prior doses of vaccine 6) concern that mutations have altered the virus since the vaccine was originally made 7) ‘two doses were enough’ and 8) ‘waiting for mix-and-match vaccines’
- Although the survey did not specifically include questions about adverse reactions, 3 of the 795 comments mentioned minor side effects following 3rd dose. They were transient tiredness, fever, body ache and throat discomfort.
- We had previously reported the adverse effect profile of the primary vaccination series in India (8). We found that a sizable proportion of people (44%) reported no known history of COVID-19 so far. It is possible that many in this group had asymptomatic infections, or had not been tested. Since the respondents belonged to diverse demographic groups, we believe that we got a true representation of the community from a wide geographic distribution. Most people did not know the exact source of picking up the infection, but workplace (medical outpatient clinic for healthcare workers), spouse and child were the most frequently cited sources.
- A large number of people (15% of those with a history) reported having COVID-19 more than once. Among them, 454 people had it twice, 26 people thrice and a few individuals reported up to 5 times. This is consistent with observations elsewhere about reinfections being common (9). The reinfection percentage of 15% is likely to be an underestimate because several respondents clarified that in subsequent episodes with compatible symptoms, testing was not always done. Unfortunately, it is not possible to verify each one of these cases because the survey is entirely self-reported. It is likely that a few of these episodes were self-diagnosed.
- The 3rd wave infection rates were almost identical (39 and 40%) across the two main vaccines used in India, which are Covishield (adenovirus vector) and Covaxin (inactivated), when used as primary series. When these vaccines were used as 3rd dose, the third wave infection rates were identical at 30%. Among those few respondents who had taken other vaccines (breakdown not available due to survey constraints), the third wave infection rate was 29%.
- Using the survey, we tried to determine whether the infection rate depended on how recent the vaccination was. We found that the longer the gap after second dose, the greater the likelihood of becoming infected during 3rd wave. Accordingly, the percentage of 3rd wave infection was only 27% among people who had recently received a second dose (Figure 8). This was nearly the same as 30% among those who recently received a 3rd dose. This suggests that proximity to the most recent vaccine dose – whether it was the second or the third – is an important determinant of protection from infection.
- This is consistent with reports that for corona viruses, protection from reinfection is short-lived (10). We also found that among those who had taken their second dose, adding a third dose without sufficient gap did not confer any additional protection from infection (Figure 8b). When the 3rd dose was given after a 6-month gap, there was a 19% reduction in the risk of infection.
- This suggests that frequent vaccine doses will not add anything further to pre-existing protection from infection. Among those who reported severe disease, 15% were reinfections.
- We contacted individuals who had repeated episodes of COVID-19, and asked them whether the second episode was milder. From the limited number of individuals that could be reached, no consistent pattern was apparent; some said the second bout was more severe, a few said that they were equally severe requiring several days of rest, others said it was milder. This is an area that needs further study, especially considering the seemingly endless risk of reinfections in the years to come. If large studies of reinfections show that subsequent bouts cause more severe disease, mitigation measures will need to be upgraded.
- The strength of the study was the large number of respondents and the diverse demography, which are reassuring of a balanced sample. That 44% of respondents did not report COVID-19 was an indication that the results were not skewed in any direction, and presented a broad picture of the general population as the country went through its third wave. The comments section served two purposes. It encouraged anonymous sharing of personal views without constraint, thus generating a positive user experience, indirectly leading to greater survey referrals. The descriptive comments entered by 795 respondents also helped corroborate the main survey findings.
- The limitations of our study are that because it was a survey, all the data provided could not be independently verified. All positive and negative cases were based on self-reported information. Besides, limitations in language proficiency in individual cases could have affected the quality of the response. While analysing the data, we did however talk with several respondents by phone, where contact information was provided. A significant limitation was that the number of unvaccinated individuals was small, constituting only 1.4% of the total number of respondents. Therefore, a meaningful comparison of their disease profile was not possible.
- A cross-sectional survey is a descriptive research tool that provides a broad snapshot of society at a given time-point, and is not to be equated with a case-control study or a randomised trial that are able to select the participants and oversee data collection. Although useful to study disease patterns across large sections of the population, a survey is therefore not a method that can be used to calculate effectiveness of interventions like booster doses.
- Among those who took the third dose, nearly one-third reported COVID-19 during the third wave. Although less than one percent had severe symptoms during 3rd wave, 41.5% reported symptoms of moderate severity.
- Younger adults were preferentially affected. There was no difference between vaccine type and 3rd wave infection rate. Among vaccinated individuals who had not received 3rd dose, 45% reported COVID-19 during the 3rd wave. However, this group had significantly lower use of N95 masks (50%) than the 3rd dose group (68%), which may have contributed to higher infection rates.
- The 3rd wave symptom severity profile was similar among those who took 3rd dose and those who had primary vaccination series.
- Repeated bouts of infection were reported by 15%, this number is likely to be an underestimate due to diminishing testing rates.
- Reinfections were not necessarily milder. A longer gap after second dose correlated with greater chance of being infected in 3rd wave.
- Among those who had recently received their second dose, only 27% (59/221) were positive in the 3rd wave, which was about the same as that following the 3rd dose (30%). This suggests that infection was less likely among those who had recently received a vaccine dose. 3rd dose, given too close to the second dose made no difference in the infection rate. Although the respondents were 98.6% vaccinated at baseline, there was considerable uncertainty (65%) amongst them about the benefit of a 3rd dose.
- Vadrevu et al. Persistence of immunity and impact of a third (booster) dose of an inactivated SARS-CoV2 vaccine, BBV152; a phase 2, double-blind, randomised controlled trial medRxiv preprint doi: https://doi.org/10.1101/2022.01.05.22268777; this version posted January 8, 2022
- Munro et al Safety and immunogenicity of seven COVID-19 vaccines as a third dose (booster) following two doses of ChAdOx1 nCov-19 or BNT162b2 in the UK (COV-BOOST): a blinded, multicentre, randomised, controlled, phase 2 trial. The Lancet, Volume 398, ISSUE 10318, P2258-2276, December 18, 2021
- PIB’S BULLETIN ON COVID-19, 8 March 2022 https://pib.gov.in/PressReleasePage.aspx?PRID=1804058
- Gunnhild Helmsdal, Olga Kristina Hansen, Lars Fodgaard Møller, Debes Hammershaimb Christiansen, Maria Skaalum Petersen, Marnar Fríðheim Kristiansen, Omicron Outbreak at a Private Gathering in the Faroe Islands, Infecting 21 of 33 Triple-Vaccinated Healthcare Workers, Clinical Infectious Diseases, 2022;, ciac089, https://doi.org/10.1093/cid/ciac089 25 April 2022
- Alex Sigal, Ron Milo Waasila Jassat. Estimating disease severity of Omicron and Delta SARS-CoV-2 infections Nature Reviews Immunology 12 April 2022 https://www.nature.com/articles/s41577-022-00720-5
- COVID-19 Treatment Guidelines, National Institute of Health https://www.covid19treatmentguidelines.nih.gov/management/critical-care/oxygenation-andventilation/
- Maslo C, Friedland R, Toubkin M, Laubscher A, Akaloo T, Kama B. Characteristics and Outcomes of Hospitalized Patients in South Africa During the COVID-19 Omicron Wave Compared With Previous Waves. JAMA. 2022;327(6):583–584. doi:10.1001/jama.2021.24868
- Dr Rajeev Jayadevan, Dr Ramesh Shenoy, Ms. Anithadevi TS Survey of symptoms following COVID-19 vaccination in India. medRxiv preprint doi: https://doi.org/10.1101/2021.02.08.21251366, February 12, 2021.
- Weekly national Influenza and COVID-19 surveillance report Week 12 report, UKHSA 24 March 2022 https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_dat a/file/1062976/Weekly_Flu_and_COVID-19_report_w12.pdf
- Marta Galanti, Jeffrey Shaman, Direct Observation of Repeated Infections With Endemic Coronaviruses, The Journal of Infectious Diseases, Volume 223, Issue 3, 1 February 2021, Pages 409–415, https://doi.org/10.1093/infdis/jiaa392
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