RSV Surge in Children Likely Caused by ‘Immunity Gap,’ Not COVID-19 Vaccine

Fact Check

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SciCheck Digest

Hospitals across the country are seeing a spike of respiratory syncytial virus infections among children. Experts say the spike is most likely caused by an immunity gap created by the lack of exposure to the virus over the past couple of years. There’s no evidence the pediatric COVID-19 vaccine is the cause, as viral posts falsely claim.

Children’s hospitals across the United States are reporting full capacity due to an intense and early surge of respiratory syncytial virus infections. RSV is a common respiratory virus that usually causes mild flu-like symptoms, but can be dangerous for some people, especially older people, infants and young children.

By the end of October, the Centers for Disease Control and Prevention reported its surveillance systems were showing an increase in RSV detections and RSV-related emergency room visits and hospitalizations in multiple areas of the country, with some regions nearing seasonal peak levels, which usually occur from later December to mid-February. Each year, 58,000 to 80,000 children under 5 are hospitalized due to RSV infection, according to the agency.

“There are bad RSV years and less bad RSV years,” Dr. Paul A. Offit, a vaccine expert and pediatrician at the Children’s Hospital of Philadelphia, told us in an interview. “This is the worst RSV year we’ve ever seen in our hospital.”

Many experts believe the spike in RSV is primarily due to reduced immunity to the virus in the population as a result of the precautions taken during the pandemic, such as social distancing. Offit said the restrictions established in 2020 to prevent the spread of COVID-19 virtually eliminated other respiratory viruses, creating an “immunity gap.”

With fewer people having been recently exposed to the virus, fewer people have immunity against it and more people are susceptible to falling ill. This includes very young babies, who are at high risk of RSV and can be protected by maternal antibodies passed to them in utero, as well as slightly older children who may have never been infected. Now, with more people not wearing masks or isolating when feeling sick, RSV and other respiratory viruses are spreading more freely. Because a larger number of people will now get sick, more people will also become severely ill.

RSV, which normally infects nearly all children before the age of 2, is highly contagious and spreads when an infected person coughs or sneezes near other people, or through contaminated surfaces. People with RSV are usually contagious for three to eight days, but some infants and immunocompromised people can continue to spread the virus for as long as four weeks.

Opponents of the vaccine are incorrectly suggesting online that the unusually high number of infections is caused by the pediatric COVID-19 vaccines.

An Instagram user who shared a screenshot of a tweet that linked the RSV spike to the pediatric COVID-19 vaccines wrote: “Are we surprised!? Your precious sh0ts that are saving so many lives 🙄 are causing higher rates of RSV… SHOCKER I love $cience.”

“It’s the shots, per their own trial data,” reads another Instagram post, which shares this headline of a Substack post published on Oct. 29: “Evidence Suggests the COVID Shots Are Responsible for Soaring RSV Cases Throughout the U.S. & Canada.”

Del Bigtree, who leads the anti-vaccine group Informed Consent Action Network, dismissed the immunity gap argument on his Nov. 1 online talk show. Instead, he incorrectly suggested the most “obvious” explanation for the rise in RSV cases in children is the pediatric COVID-19 vaccine.

“It shows you how desperate they are to protect the vaccine, because the vaccine should be the obvious,” he said when presented with the immunity gap reasoning. “Why do we suddenly have outbreaks of RSV beyond anything we’ve ever seen before? Could it possibly be that injection that we know lowers the immune system and showed within 28 days an increase in RSV?” he said.

As we’ve reported, there is no evidence that the COVID-19 vaccines impair immunity generally, and they increase immunity against SARS-CoV-2, the virus that causes COVID-19. This is not the first time Bigtree or his group, ICAN, has spread misinformation about the vaccines — ICAN recently published a misleading analysis of COVID-19 vaccine safety data, as we reported.

“There is no evidence indicating COVID-19 vaccination can cause infection with respiratory syncytial virus (RSV),” Kate Grusich, a CDC representative, told us in an email.

The CDC also noted that COVID-19 vaccination in the youngest children remains low — less than 8% of children under 5 years old have received at least one dose, a coverage that “does not account for the surge in RSV cases seen nationally.”

“In addition, children under six months of age, who have always been at the highest risk of RSV-associated severe disease and hospitalization, continue to have the highest rates of RSV hospitalization among all age groups (RSV-NET Interactive Dashboard | CDC) – and this group is not yet eligible to receive a COVID-19 vaccine,” Grusich wrote.

No Causal Association Between RSV and COVID-19 Vaccines

Bigtree’s speculation comes from RSV cases reported after vaccination in the pediatric mRNA COVID-19 vaccine trials. Both Moderna and Pfizer/BioNTech reported a few RSV cases in the vaccine and placebo groups 28 days after vaccination, with a slightly bigger number in the vaccine group. Both companies and the Food and Drug Administration dismissed any causal association.

Moderna found that in the 6- to 23-month-old group, 0.8% of the babies that received the vaccine reported RSV, compared with 0.5% in the placebo group. In the 2- to 5-year-old cohort, 0.4% reported an RSV infection in the vaccine group and less than 0.1% in the placebo group, and in the 6- to 11-year-old cohort, 3.9% reported RSV in the vaccine group and 2.5% in the placebo group.

“All events were assessed as not related to study vaccine by the investigators. FDA agrees with the investigator assessments that there is unlikely to be a causal association between the occurrence of these events and the study vaccine. Imbalances between mRNA-1273 and placebo groups in specific respiratory infections were not observed in older age cohorts, and there is not a clear biological mechanism that would explain a causal association for certain respiratory infections but not others,” the FDA document reads.

“Overall, the frequency and clinical course for these events do not appear unusual given the age group of the young pediatric study population and the season (fall-winter) during which the study took place, and the observed imbalance could be due to chance. It is also possible that the observed imbalance could be due to an unappreciated bias associated with differences between treatment groups in risk avoidance for viral infections in general, health seeking behaviors, or clinical evaluation of suspected viral illnesses,” the document continues.

In the Pfizer/BioNTech trial, five participants in the 6- to 23-month-old group reported RSV bronchiolitis in the vaccine group, compared with three who reported bronchiolitis or RSV bronchiolitis in the placebo group. Both Pfizer and the FDA determined these events were not related to the vaccine.

A Pfizer media representative told us there is no possible mechanism that would explain a causal association between the spike in RSV cases and the COVID-19 pediatric vaccines.

“The Pfizer-BioNTech COVID-19 vaccine does not contain any part of a live virus either of SARS-CoV-2 or RSV. The pediatric vaccine does not cause COVID-19 or RSV. It is also important to note that they are completely separate respiratory viruses,” the company representative wrote in an email.

Yet, ICAN’s post demanding “ANSWERS FROM THE CDC ABOUT SPIKE IN RSV RATES” continues to spread. The group sent a letter to the CDC’s director, Rochelle Walensky, asking the agency to share the percentage of children with RSV cases who had received a COVID-19 vaccine before.

ICAN’s lawyer, Siri Aaron, did not reply to a request for comment.

Immunity Gap Explanation

Dr. Clarence Buddy Creech, professor of pediatrics at Vanderbilt University Medical Center and director of the Vanderbilt Vaccine Research Program, told us there is no evidence to support ICAN’s suggestions.

“There’s simply no indication that getting a COVID vaccine changes how you respond to RSV,” he wrote in an email.

“The differences between vaccine and placebo groups” were “very small for RSV,” he said. And he added that people should also keep in mind that viral infections are diagnosed more frequently in the clinical trials than they would be in the real world because of the intense surveillance.

Creech said he and others think the spike in RSV “is principally due to a relative lack of immunity in young children since the burden of RSV and influenza have been remarkably lower during the pandemic (likely due to masking, social distancing, school closures, and keeping children home while ill).”

This does not mean that taking precautions during the pandemic was a bad idea, nor does it mean that people should seek out infections. The “immunity gap” concept, which sometimes is referred to as “immunity debt” or “immune debt,” should not be confused with the unsupported idea that reduced exposure to viruses such as RSV damages an individual’s immune system. But surges in viral infections are expected when immunity to those viruses declines in the population.

Indeed, the current spike is not a surprise to experts who’ve been watching a disruption in the circulation of seasonal viruses. A study published in Nature Communications in May showed “a major shift in the epidemiology of RSV in Australia” after the emergence of the virus that causes COVID-19, with “large scale outbreaks” occurring out of season in 2020-2021.

“There was no typical winter surge in hospitalisations related to RSV among children in 2020,” a group of experts in infectious diseases from the University of Colorado School of Medicine and researchers from the ecology and evolutionary biology department at Princeton University wrote in a commentary published in the Lancet in July.

“As NPI measures were further relaxed, interseasonal RSV outbreaks began the following spring, with waves of disease affecting older than the typical median age for childhood RSV-associated respiratory infections,” they continued, referring to nonpharmaceutical interventions, or actions that people can take to prevent the spread of a virus, such as social distancing.

The lack of exposure to endemic viruses created an immunity gap, the researchers explained, in which there is “a group of susceptible individuals who avoided infection and therefore lack pathogen-specific immunity to protect against future infection.” The pandemic disruptions in the health care system also resulted in fewer childhood vaccinations, they argued.

“The cumulative effect of new susceptible birth cohorts, waning immunity over time with decreased exposures to usual endemic viruses, and lagging vaccination rates in some settings widens this immunity gap and increases the potential for future outbreaks of endemic viruses,” they wrote.

The group warned hospitals to be prepared for “larger outbreaks occurring out of season among older children and with atypical presentations.”

“We knew it was inevitable that these diseases would come back,” Kevin Messacar, one of the researchers, told CNN, referring to RSV and other respiratory illnesses caused by endemic viruses.

There is no vaccine to prevent RSV yet, but several candidates are in development. Pfizer recently announced its RSV vaccine showed promising results and that it would seek FDA approval by the end of the year.

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