When Delta and Influenza Intersect


With the Delta cases surging in recent weeks, and the upcoming flu season almost upon us, here is a glimpse of what providers and the public can expect when both viruses are circulating.

In early July, control of COVID-19 seemed to be trending in the right direction including vaccinations increasing, caseloads going down and a sense the pandemic might become somewhat under control.

When Pfizer began advocating for booster doses in early July, officials from the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH) told Pfizer officials that relevant data supporting a COVID-19 booster dose remained inconclusive.

By August, the Delta surge which had torn through the United Kingdom and India earlier in the year, was now in the United States and creating havoc as caseloads went up, including hospitalizations, increases in mortality, and the emergence of breakthrough infections. This very acute surge was perplexing to public health officials as well as the general public, especially to those who were vaccinated.

Addressing the Shifting Vaccination Policy

Just weeks before, the FDA and CDC did not see the utility of a booster dose. Then in August, the Biden Administration began publicly advocating for a booster dose months after the second dose of the vaccine. Initially, it was 8 months and then there were reports it has decreased to 6 months after the second dose.

And for those who are already vaccinated, booster doses will likely be available for some people this fall and winter including the immunosuppressed, people 65 years and older, and health care workers. Last week, the Vaccines and Related Biologic Products Advisory Committee (VRBPAC) decided to create a new question to vote on an Emergency Use Authorization (EUA) for a booster dose for people 65 years and older and those deemed high risk of COVID-19. That vote passed unanimously in favor of those two groups being eligible for the booster dose. In addition, they created a poll question during the meeting addressing health care workers (HCW) and that also passed unanimously in favor of HCWs being eligible for boosters.

This shift in health care policy came largely from data from Israel, which saw a COVID-19 surge of its own this year, leading to more hospitalizations and higher mortality rates. That country decided upon a booster strategy to bring down incidence rates.

It is important to note, VRBPAC members at the September 17 meeting, discussed their reservations to recommending an approval for booster doses for the Pfizer-BioNTech COVID-19 vaccines for everyone 16 years and older, and a large part of their reasoning was due to the fact there was very limited data to demonstrate the need in the United States to give everyone a third dose.


In the background behind the Delta surge and the discussion on boosters, is the impending flu season. Last year it did not develop into a large concern due to all the restrictions related to COVID-19. The influenza season was the lowest it had been in years.

However, in 2021, with many restrictions lifted, people vaccinated, and life getting back to normal, there will be more person-to-person interactions and the possibility of more people getting influenza. With this possibility comes one of the concerns public health officials have had: “the twindemic.” This is a phenomenon where providers and the public are battling COVD-19 and influenza simultaneously.

As the southern hemisphere goes through their influenza season now, indications thus far show it has been a mild season there. Flu activity worldwide remains very low at < 10% positivity of tested specimens.

Still, with the unpredictability of this seasonal virus and the pandemic virus and taking into consideration the risk of these viruses individually or combined, getting vaccinated should be part of everyone's care plan.

Although decisions and guidance by public health agencies are evolving depending on the latest data released from studies, in the meantime, there are vaccination health care recommendations that can be followed now.

Contagion spoke with William Schaffner, MD, medical director for the National Foundation for Infectious Diseases (NFID), professor of Preventive Medicine in the Department of Health Policy, and professor of Medicine in the Division of Infectious Diseases at the Vanderbilt University School of Medicine, who offered some guidance in terms of vaccinations, the potential of the twindemic, and the timing of booster and influenza vaccines.

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