GlobalHealth Threats

30 May 2022: Influenza vaccines reduce the risk of COVID-19 infection and severe disease. This has been reiterated through a study conducted in Qatar and uploaded to medRxiv. Researchers collected data on more than 30,000 healthcare workers who received the influenza vaccine between September and December 2020. A case was defined as one who tested positive for COVID-19 within 14 days of receiving the flu vaccine, while control was one that tested negative for COVID-19 during the same time. At least 576 cases and over 10,000 controls were studied further. Only one case progressed to severe illness and none were critical or fatal. On the contrary, of the COVID-19 positive participants who did not receive the flu vaccination, 17 got a severe infection and two were critical. Researchers concluded that the estimated effectiveness of the flu vaccine against SAR-CoV-2 was about 30%, while the reduction of severe infection was about 90-95%.

15 September 2021: A pre-print journal article, uploaded to medRxiv, claims there may be non-specific boosting of immunity following influenza vaccination which confers some benefits against infection with COVID-19. It is important to stress that this article has not yet been subject to peer review and independent evaluation and therefore while it points to some benefit, further scrutiny is expected. Their findings suggest between one third and one half relative risk reduction for patients vaccinated against influenza with an inactivated quadrivalent (containing four flu strains) vaccine although there are a number of factors which could contribute to these findings.

The study considered hospital employees of the Radboud University Medical Centre in the Netherlands and used databases of employees' vaccination status and subsequent diagnoses with COVID-19 in the first and second waves of COVID-19. In the autumn/winter of 2019, around 53% of the employees had been vaccinated against influenza. In the first wave, they found that 3.34% of the individuals who were not vaccinated against influenza went on to have COVID-19, compared to 2.11% of the vaccinated employees. This is a relative risk reduction of around 37% (RR=0.63, 95% CI, 0.47-0.84, P=0.0016). The following year, the hospital’s total influenza vaccination coverage rate during the 2020/2021 influenza season was 42%. The COVID-19 infection rate during the second wave was 3.92% among unvaccinated employees and 2.00% for vaccinated employees. This is a nearly 50% relative risk reduction (RR of 0.51, 95% CI 0.40-0.65, P < 0.0001).

The researchers also examined possible mechanisms for this apparent protective effect and detail their findings in the detailed paper. The authors are keen to point out that flu vaccination is no substitute for the now available COVID-19 specific vaccination but were investigating whether flu vaccination could offer a bridge during the time COVID-19 specific vaccines were being developed and deployed.

6 August: A study published in PLOS ONE looks into the potential benefits of influenza vaccine against COVID-19. The study used Electronic Medical Record (EMR) from 56 healthcare organizations distributed across the United States, the United Kingdom, Italy, Germany, Israel and Singapore. Results show that patients who tested positive for SARS-CoV-2 who received the influenza vaccine experienced decreased sepsis and stroke, and lower emergency and Intensive Care Unit admissions. This suggests a potential protective effect that could benefit populations, particularly those that do not have easy access to COVID-19 vaccines.