Perfect storm of SARS-CoV-2 during flu season


COVID-19 now. The urban phase of the U.S. pandemic is leveling somewhat, while the rural phase is accelerating – in part because of food processing and handling industries. The pediatric burden has been surprisingly small, with the multisystem inflammatory disease (MIS-c) in children noted in several hundred cases now being seen across the country.


Next wave? Given ongoing COVID-19 disease, controversy rages about when and how to re-open the country. Regardless how more reopening occurs over the next months, we should expect a next or ongoing COVID-19 wave, particularly given loss of social distancing during social justice protests. A sawtooth disease prevalence pattern is predicted by many experts: a drop in prevalence leading to reopening, leading to scattered prevalence increases and regional if not local restriction tightening, followed by another drop in prevalence. Then “rinse and repeat” until 70% of the population is immune either by disease experience or vaccine-induced immunity, likely sometime in 2021.

Influenza too. A COVID-19 up-cycle is likely during influenza season, although influenza season’s onset could be altered because of whatever social distancing rules are in place in November and December. That said, we need to consider the worst. We have seen what happens if we fail to prepare and then react only after a prevalent respiratory infection has surged into the overall population. Best estimates are that at most 20% of the U.S. population is currently immune to SARS-CoV-2. Given that at least some of that 20% of individuals currently immune to SARS-CoV-2 will lose their neutralizing antibody over the next 4-6 months, we can still expect 70%-80% of the U.S. population to be susceptible to SARS-CoV-2 infection in the fall of 2020.

Pediatric preparedness. As pediatric providers, we have struggled with lower patient loads and dramatic income losses/declines. Many clinics/offices’ attendance remain less than 50% of pre–COVID-19 levels, with necessary furloughs of personnel and spotty office hours. But influenza is coming, and SARS-CoV-2 will not be gone yet. How do we prepare for concurrent influenza and COVID-19?

Dr. Christopher J. Harrison, professor of pediatrics and pediatric infectious diseases at Children’s Mercy Hospitals and Clinics, Kansas City, Mo.

Dr. Christopher J. Harrison

The annual purchase/administration of influenza vaccine in summer/fall is expensive, time consuming, and logistically difficult even in the best times. Given the loss of income, likely reluctance of patients to come to clinics/offices if COVID-19 is still circulating, and likely need for some form of social distancing during late summer and early fall, how will providers, health departments, and hospitals implement influenza vaccine administration this year?

Minimize double whammy infections. Maximizing influenza vaccine uptake during the COVID-19 pandemic is super important. It is easy to understand why we should maximize influenza protection in SARS-CoV-2 vulnerables (elderly or persons with existing comorbidities). But is it as critical for otherwise healthy children? My answer is yes.

Children are not currently known as SARS-CoV-2 vectors, but children are excellent influenza vectors, shedding higher titers for longer than other age groups. As with SARS-CoV-2, influenza exposure is cumulative, i.e., the more intense and more frequently a person is exposed, the more likely that infection/disease will result. So, the fewer who get and can transmit influenza during the COVID-19 pandemic, the fewer people are likely to get a double whammy of SARS-CoV-2 concurrent or in tandem with influenza. Double whammy infections likely would further increase the medical care burden and return us to March-April crisis mode.

One alarming new question is whether recent influenza could make children vulnerable to SARS-CoV-2 and trigger hospitalizations. A surge in pediatric plus adult COVID-19 disease plus a surge in all-ages influenza disease would likely break the medical care system, at least in some areas.


Staggering COVID-19 burden. As of June 8, we have had approximately 2 million SARS-CoV-2 cases with 500,000 hospitalizations and 120,000 deaths. Over the past 10 years, total annual U.S. influenza hospitalizations ranged from 180,000 (2011-2012) to 825,000 (2017-2018). The interquartile range for hospitalization length of stay for influenza is 4-6 days1 vs. 15-23 days2 for SARS-CoV-2. One COVID-19 hospitalization uses hospital resources roughly equal to four influenza hospitalizations. To date COVID-19 hospitalizations have used resources equal to an estimated 1.9 million influenza hospitalizations – over twice the worst influenza season in this century – and we are still on the rise. We are likely not even halfway to truly controlling the U.S. pandemic, so expect another 500,000 hospitalizations – equal to another 1.9 million influenza hospitalizations. Further, pneumonia deaths have skyrocketed this year when COVID-19 was superimposed on the last third of influenza season. One hope is that widespread use of antivirals (for example, new antivirals, convalescent plasma, or other interventions) can reduce length of stay by 30% for COVID-19 hospitalizations, yet even with that the numbers remain grim.

Less influenza disease can free up medical resources. Planning ahead could prevent a bad influenza season (for example, up to 850,000 hospitalizations just for influenza). Can we preemptively use vaccine to reduce influenza hospitalizations below 2011-2012 levels – less than 150,000 hospitalizations? Perhaps, if we start by reducing pediatric influenza.

1. Aim to exceed 75% influenza vaccine uptake in your patients.

a. It is ambitious, but if there was ever a year that needed influenza herd immunity, it is 2020-2021.

2. Review practice/group/institution plans for vaccine purchase and ensure adequate personnel to administer vaccine.

3. Plan safe and efficient processes to vaccinate large numbers in August through November.

a. Consider that routine and influenza vaccines can be given concurrently with the annual uptick in school and sports physical examinations.

b. What social distancing and masking rules will be needed?

i. Will patients need to bring their own masks, or will you supply them?

c. What extra supplies and efforts are needed, e.g. hand sanitizer, new signage, 6-foot interval markings on floors or sidewalks, families calling from parking lot to announce their arrivals, etc.?

d. Remember younger patients need two doses before Dec 1, 2020.

e. Be creative, for example, are parking-lot tents for influenza vaccination feasible?

f. Can we partner with other providers to implement influenza vaccine–specific mass clinics?

Ramping up to give seasonal influenza vaccine in 2020 is daunting. But if we do not prepare, it will be even more difficult. Let’s make this the mildest influenza season in memory by vaccinating more than any time in memory – and by doing so, we can hope to blunt medical care burdens despite ongoing COVID-19 disease.

Dr. Harrison is professor of pediatrics and pediatric infectious diseases at Children’s Mercy Kansas City (Mo.). Children’s Mercy receives funding from GlaxoSmithKline, Merck, and Pfizer for vaccine research studies on which Dr. Harrison is an investigator. Email him at [email protected].


1.. HCUP Statistical Brief #253. 2019 Oct.

2. medrxiv. 2020 Apr 10. doi: 10.1101/2020.04.07.20057299.

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