In the winter of 2021/22, both SARS-CoV-2 and seasonal respiratory viruses, primarily influenza, will co-circulate. Coronavirus and flu can be contracted at the same time. This coinfection increases the risk of severe illness and death.

Scientists from the National Infectious Disease Service of England have investigated:

  • whether influenza infection is associated with a reduced risk of SARS-CoV-2 coronavirus infection;
  • whether coinfection with coronavirus and influenza is associated with a more severe SARS-CoV-2 outcome, such as death, hospitalization, admission to an intensive care unit, or the need for mechanical ventilation (ALV).

The study involved 19,256 people who were tested for influenza and SARS-CoV-2 between January and April 2020:

  • 58 people were coinfected with SARS-CoV-2 and influenza;
  • 992 people tested positive for flu and were harmful to SARS-CoV-2;
  • 4443 people tested positive for SARS-CoV-2 and were negative for influenza;
  • 13,763 people tested negative for both SARS-CoV-2 and influenza.

Impact of Influenza Infection on The Risk of Disease With SARS-Cov-2

Scientists found that the risk of contracting SARS-CoV-2 was 58% lower among those infected with the flu.

The likely mechanism of this effect is that in response to the first viral infection, the body produces an antiviral signaling molecule – interferon. The interferon response of the innate immune system counteracts the second viral infection.

A recent study by Chinese scientists showed that the reproduction rate of SARS-CoV-2 is lower than that of the flu. Therefore, if infections start at the same time, the coronavirus is suppressed. However, if an influenza infection occurs after infection with SARS-CoV-2, coinfection will be detected.

Scientists divided patients into age groups:

  • children (up to 19 years old);
  • adults of working age (19-65);
  • older adults (> 65).

The likelihood of contracting SARS-CoV-2 in working-age and older people was significantly lower with a positive influenza test. Conversely, in children, there was no association between a positive flu test and a positive test for SARS-CoV-2.

Coinfection with Coronavirus and Flu Increases The Risk of Death

Of the registered deaths:

  • 1% of people were coinfected with SARS-CoV-2 and influenza;
  • 52.6% had only SARS-CoV-2 infection;
  • 1.8% had only the flu;
  • 44.7% tested positive for SARS-CoV-2 and influenza.

Coinfected patients had a risk of death nearly 6 times higher than those without the flu or SARS-CoV-2 and 2 times higher than those with only COVID-19. The risk of admission to an intensive care unit or death was 6.33 times higher among coinfected individuals.

The mortality rate was higher among older people with SARS-CoV-2 coinfection and influenza.

Flu Vaccination Reduces Risk of Severe COVID-19

Influenza vaccines enhance the function of innate immune NK cells, natural killer cells that recognize and kill infected cells in the absence of antibodies.

A study by Italian scientists has shown that influenza vaccination reduces deaths from COVID-19. This effect can be explained by the fact that the influenza vaccine activated innate immunity. Therefore, when faced with SARS-CoV-2, the body was set up for a quick antiviral response.

A study by American scientists has shown that influenza vaccination over the past 1, 2 and 5 years reduces the incidence of coronavirus infection.

Dutch and German scientists have confirmed this fact: hospital staff vaccinated against the flu were less likely to become infected with SARS-CoV-2. Scientists attributed this to the fact that the flu vaccine stimulated immune cells and improved cytokine responses.

Swiss and Brazilian scientists found that COVID-19 patients who recently received the flu vaccine needed 8% less intensive care, 18% less need for invasive respiratory support, and were 17% less likely to die.

Read more about the protective effect of non-coronavirus vaccines in the article “Why non-coronavirus vaccines are effective against SARS-CoV-2.

To Protect Against Coinfection, It Is Crucial to Get Both Vaccinations from The Coronavirus and The Flu

How long should there be between flu and coronavirus shots? Order of the Ministry of Health of Russia dated 03.21.2014 N 125n “On the approval of the national calendar of preventive vaccinations and the calendar of preventive vaccinations for epidemic indications” clarifies this issue as follows: “It is allowed to administer inactivated vaccines on the same day with different syringes in different parts of the body. The interval between vaccinations against various infections when carried out separately (not on the same day) should be at least 1 month. “

Why does a month have to pass between vaccinations? In the reference book “Immunoprophylaxis-2014” (Tatochenko V.K.), published by the Union of Pediatricians of Russia, the Scientific Center of Children’s Health of the Russian Academy of Medical Sciences, this is explained as follows: “When drawing up a tight schedule, you can reduce the interval between different inactivated vaccines, the monthly gap can be justified only theoretically only for two live vaccines (inactivation of the second vaccine with interferon released in response to the first). It is possible to administer a live vaccine after an inactivated one or vice versa, as well as 2 different inactivated vaccines according to individual and epidemiological indications, at any interval. The monthly interval indicated in official documents refers to routine vaccinations. “

Conclusions

Influenza infection reduces the risk of contracting coronavirus. However, in the case of coinfection with coronavirus and influenza, the risk of admission to the intensive care unit or death increases 6 times.

Perhaps SARS-CoV-2 and influenza have a synergistic effect by facilitating the spread of the virus from cell to cell. For early detection of coinfection, influenza testing should be done in conjunction with testing for SARS-CoV-2. To prevent serious illness, flu vaccination is necessary and early administration of antiviral drugs if coinfection is detected or suspected. The flu vaccine can be obtained one month after the coronavirus vaccine.

Source

Interactions between SARS-CoV-2 and Influenza and the impact of coinfection on disease severity: A test negative design

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