Flu vaccine increases coronavirus risk 36%, says military study.
, SUMMARY  \nAn article published on the websites DisabledVeterans.org and GreenMedInfo, as well as several Facebook posts, claimed that the flu vaccine increases the risk of coronavirus infection. This claim appeared after medical professionals announced their recommendations for people to get the flu shot during the COVID-19 pandemic, as reported by the New York Times and ABC News., The DisabledVeterans.org article relies on a study by Gregg Wolff of the U.S. Armed Forces Health Surveillance Branch, published in early January 20201, claiming that the study shows that “flu vaccine increases coronavirus risk by 36%”. Scientists who reviewed the claim pointed out that although the study did report a higher probability of coronavirus infection in individuals that received the flu vaccine, it examined only seasonal coronaviruses that cause the common cold, but not SARS-CoV-2, the coronavirus causing COVID-19. As such, these results cannot be extrapolated to SARS-CoV-2., Secondly, the study did not take into account potential confounding factors such as age, which may have biased the results. Thirdly, the study by Wolff, which is based on administrative records, excluded about 20% of these records. Sheena Sullivan, associate professor at the Doherty Institute and epidemiologist for the World Health Organization (WHO) Collaborating Centre for Reference and Research on Influenza, explained: “There’s no analysis of how this might have impacted estimates in the study. Sometimes the records excluded differ from those included in meaningful ways that influence the effect estimate, so it’s important to check.”, Angeline Rouers, senior research fellow at the Singapore Immunology Network, highlighted the fact that the Wolff study itself stated that “Vaccinated personnel did not have significant odds of respiratory illnesses”., The Wolff study includes the hypothesis that vaccine-associated virus interference may lead to increased risk for other respiratory viruses in vaccinated individuals, because the flu vaccine prevents or minimizes temporary non-specific immunity conferred by natural infection. Virus interference “occurs when a virus impacts the growth of other viruses,” said Rouers. “It may be the case with influenza virus but this phenomenon is still controversial2.” Indeed, the Wolff study makes it clear that this hypothesis remains unconfirmed and that studies have so far provided mixed results, but this is taken out of context in the DisabledVeterans.org article., A study# by Skowronski et al. published on 22 May 2020, which gathered data over seven influenza seasons from 2010 to 2017, found that the flu vaccine “significantly reduced the risk of influenza illness by >40% with no effect on coronaviruses or other non-influenza respiratory virus (NIRV) risk”5. The study also identified a significant methodological flaw in the study by Wolff, resulting from an improper inclusion of influenza test-positive specimens in NIRV test-negative control groups. The authors explained that:, “Wolff adjusted for age and excluded specimens that tested influenza-positive. In that analysis, shown in his Table 3, the odds ratio (OR) approached unity indicating no vaccine effect as expected. Conversely, in unadjusted analysis of individual NIRV outcomes (e.g. coronaviruses) Wolff retained influenza test-positive specimens in NIRV test-negative control groups, thereby violating the core prerequisite for valid test-negative design analysis. In the context of effective influenza vaccine, influenza cases would have lower likelihood of vaccination; as such, their inclusion would systematically reduce the proportion vaccinated in the control group and thereby inflate ORs comparing vaccine exposure between NIRV cases and controls.”, The U.S. Centers for Disease Control and Prevention also addressed this concern:, “There was one study that suggested that influenza vaccination might make people more susceptible to other respiratory infections3. After that study was published, many experts looked into this issue further and conducted additional studies to see if the findings could be replicated. No other studies have found this effect. For example, this article in Clinical Infectious Diseases4. It’s not clear why this finding was detected in the one study, but the preponderance of evidence suggests that this is not a common or regular occurrence and that influenza vaccination does not, in fact, make people more susceptible to other respiratory infections.”, A scientific study by Cowling et al. has also been used to support the claim3. This study specifically examined the risk of non-influenza respiratory infections in children who received the inactivated trivalent influenza vaccine. Sullivan pointed out that the study “did suggest increased risk of non-influenza viruses among kids who were vaccinated, but it says nothing about increased risk for seasonal coronavirus infection. Only two cases of coronavirus out of 115 cases of respiratory infection are mentioned in the paper.” She also cautioned that the study included only children, so it is difficult to say whether the same trend would occur in adults., In summary, the question of whether the flu vaccine causes an increased risk of coronavirus infection requires more scientific studies to answer. While the studies by Wolff and Cowling et al. suggest a potential increase in the risk of viral respiratory infections after receipt of the flu vaccine, another much larger study found no significant difference in risk between vaccinated and unvaccinated groups4. This study monitored individuals over six influenza seasons, whereas the two studies cited in the claim covered only one influenza season., To be clear, despite suggestions even from top politicians that the flu vaccine protects against COVID-19, this has not been substantiated. However, the vaccine can provide several indirect benefits during this pandemic, such as reducing the risk of flu infections, thereby reducing cases of flu complications like pneumonia that require hospitalization. This “will reduce the burden on hospitals and ensure that facilities are available for patients in need,” said Rouers. This is the same goal driving the popular “flatten the curve” catchphrase: preventing the healthcare system capacity from being overloaded., In addition, it is also possible to be infected with both influenza and SARS-CoV-2 at the same time, as this case report from China shows, although how common this is and whether co-infection would affect a patient’s clinical outcome is still unclear., “We definitely want to avoid people having a flu at the same time as potentially having coronavirus—so having two infections and the body becoming overwhelmed,” said Holly Seale, a senior lecturer in the School of Public Health and Community Medicine at the University of New South Wales, in this ABC News report. She added that “health authorities wanted to avoid people presenting to their local hospital or GP with seasonal flu, which could put them at increased risk of catching another virus, including coronavirus.”, SCIENTISTS’ FEEDBACK  \n Angéline Rouers, Research Fellow, Singapore Immunology Network:\nThe article and the Facebook posts claim that the flu vaccine increases the risk of infection by other respiratory viruses, such as coronavirus. This is based on a recent scientific article published in the journal Vaccine in January 20201. However the scientific publication itself is not so definitive in its conclusions. We just have to read the Highlights at the top of the article: “Vaccinated personnel did not have significant odds of respiratory illnesses” and “Odds of virus interference by vaccination varied for individual respiratory viruses”., The associated risk of infection by other respiratory viruses in the vaccinated group does exist, but it remains low and limited to human metapneumovirus and coronavirus according to this study. Coronavirus is a family of viruses but this study did not look at COVID-19 specifically, so it can be misleading for readers in the current context. Also good to highlight that it’s difficult to establish a direct link between this observation and the vaccine., As suggested, this potential increased risk of infection by other respiratory viruses might come from a phenomenon known as viral interference. It occurs when a virus impacts the growth of other viruses. It may be the case with influenza virus but this phenomenon is still controversial2. The hypothesis is that the flu vaccine (by protecting against influenza virus) could give the opportunity to other viruses to infect the host. Since this hypothesis is not clearly demonstrated and due to the mortality rate from influenza every year, it is probably better to continue to get vaccinated., These viral posts followed recommendations in mainstream news to get a flu vaccine to be protected during the COVID-19 pandemic. However, the posts take these mainstream news articles out of context, which is misleading for the general public: the news articles did not mean that the flu vaccine can protect against coronavirus, but that being protected against flu and its complications will reduce the burden on hospitals and ensure that facilities are available for patients in need., Sheena Sullivan, Associate Professor, Doherty Institute:\nSome comments on the Wolff article1:, The Cowling paper describes potential temporary non-specific immunity3:, Another paper by Sundaram et al. reported no association between influenza vaccination and coronavirus4. I couldn’t find any other studies reporting on that specific relationship., In general there is very weak evidence supporting concerns that influenza viruses may lead to increased risk of seasonal coronavirus infection. More evidence is needed., Hanif Javanmard Khameneh, Postdoctoral Researcher, Institute for Research in Biomedicine, University of Lugano:\nThe paper published on the study conducted by the U.S. Department of Defense indicates that the incidence of some viral infections in individuals who received the flu vaccine is higher in the study group versus non-vaccinated individuals1. While this study deserves the attention of epidemiologists as well as virologists and immunologists in the field for further investigation, it has some shortcomings in design and implementation, hence the results has to be interpreted very carefully:, A fact-check by Lead Stories reported this claim to be “not true”., #: Added new information from a study by Skowronski et al.5, which provided further evidence that the flu vaccine does not increase risk of coronavirus infection, and also identified a significant methodological flaw in the study by Wolff., 2019-nCoV \xa0Coronavirus \xa0COVID-19 \xa0Flu \xa0Influenza \xa0Respiratory infections \xa0Vaccine, Published on: 30 Mar 2020 | Editor: Flora Teoh, Health Feedback is a non-partisan, non-profit organization dedicated to science education. Our reviews are crowdsourced directly from a community of scientists with relevant expertise. 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Claim that flu vaccine increases coronavirus infection is unsupported, misinterprets scientific studies - Health Feedback