Immunising the population against covid-19 does not make it more vulnerable to influenza

You have sent us a video through WhatsApp claiming that the Spike protein, the one in which vaccines are based and which is found in the surface of SARS-CoV-2, has the capacity to worsen influenza disease, which will cause during autumn and winter months “a large mortality”. And provides numbers: according to the video, about “20% and 30% of vaccinated people” will die. This is FALSE. There is no scientific evidence that vaccination against covid-19 influences in any way the development of the most severe influenza cases. These are different diseases, caused by different viruses and the presence or absence of the S protein does not influence the development of influenza.

"One of the problems that this type of protein (S) causes is that, when there is an influenza epidemic, in autumn or winter, when something similar or worse happens, 20% to 30% of those vaccinated are going to die" 

The video protagonist, who self-identifies as Maria José Martínez Albarracín and who says to have been member of “Doctors for the truth”, an organisation denying that there is currently a pandemic in Spain, details along the whole interview the alleged long-term effects and affirms that it is able to worsen other common ailments such as influenza. 

All of the approved vaccines to date are designed to teach the immune system to detect the S protein, placed at the surface of coronavirus so that, in case of infection, the body knows how to fight it. That is, when we receive the injection of the covid-19 vaccine, a response to this protein is triggered. Adelaida Sarukhan, immunologist and scientific writer at the Institute for Global Health (ISGlobal, in Catalan) in Barcelona, explains to Verificat that "there is no relationship, at the level of immune response, between covid-19 and influenza. They are completely different viruses and no cross-immunity —that which is generated after someone has been exposed in the past to a similar pathogen and thanks to which some protection is generated against similar viruses— is observed". Therefore, he continues, being vaccinated against covid-19 "will neither improve nor worsen our response to an influenza virus infection".

Although both the flu and covid-19 viruses show in some occasions a similar symptomatology (fever, dry cough, sore throat), they are diseases caused by different viruses: flu is caused by influenza virus, causing a respiratory disease,while covid-19 is produce by SARS-CoV2, a coronavirus first identified in 2019, and which causes an infectious disease which, although in most of the cases affects the respiratory tract, "it also has the potential to infect numerous organs and to generate a great clinical diversity of manifestations", as indicated in this document published by the Instituto de Salud Carlos III (Madrid). 

Less prepared for the flu

Another thing is that hospitalisations may increase due to a rise in cases of both diseases, something scientists do not rule out: "Unlike this winter, we may have a double burden of hospitalisations due to covid (in unvaccinated or partially vaccinated people) and influenza this autumn, if non-pharmaceutical measures (use of masks, indoor ventilation, social distance) are relaxed too much," points Sarukhan.

Measures to slow down coronavirus infections have also led to a decline in influenza cases, which has also caused "some loss of immunity to them", says Sarukhan, citing the example of respiratory syncytial virus, the most common microbe that causes lung and respiratory tract infections in infants and children, and whose cases have risen sharply in children in recent weeks.

Vaccines do not worsen other diseases

Beyond influenza, "there is no reason why covid vaccination could aggravate other diseases or infections," says Sarukhan. But it would not be far-fetched either: scientists are talking about a phenomenon called antigenic imprinting or original antigenic sin, which sometimes means that when the immune system is confronted with a pathogen similar (but not identical) to one to which it has already developed antibodies, the type of response that developed in the first encounter dominates. 

This can be a good thing (the famous cross-immunity) if previous antibodies are effective against that new pathogen, but it does not always have to be the case, which is known as the original antigenic sin: "There would be a possibility that future covid-19 vaccines could be less effective against other variants in people who have already developed an immune response against the original SARS-CoV-2 variant. However, there is currently no evidence (in the lab or in the field) that this will be a problem," concludes the immunologist.