Due to the success of COVID-19 restrictions and public health measures such as social distancing, school closures, and mask mandates, the incidence of many common viral infections plummeted in the early days of the pandemic.
In the United States, influenza activity sharply decreased in March 2020, was historically low through the summer of 2020, and remained low during the entire 2020-2021 flu season. During September 28, 2020 - May 22, 2021 in the United States, only 1,675 (0.2%) of 818,939 respiratory specimens tested by U.S. clinical laboratories were positive for an influenza virus. Circulation of other respiratory pathogens, including respiratory syncytial virus (RSV), common human coronaviruses (HCoVs), and parainfluenza viruses (PIVs) also decreased in early 2020 and did not increase until spring 2021. Human metapneumovirus (HMPV) circulation decreased in March 2020 and remained low through May 2021. Rhinovirus and enterovirus (RV/EV) circulation decreased in March 2020, remained low until May 2020, and then increased to near pre-pandemic seasonal levels.
It became apparent as public health precautions were relaxed that common viral infections began to rise. However, they began to rise in strange and uncharacteristic ways.
Compared with influenza seasons prior to pandemic, the 2021–2022 influenza season was mild, but it occurred in two distinct waves, with a higher number of hospitalizations in the second spring wave. Influenza activity in the United States during the 2021–2022 season began to increase in November, declined in January 2022, increased again in March 2022 and remained elevated until mid-June 2022.
In the United States (US), the timing of typical RSV epidemics follows a notable pattern, with outbreaks starting earliest in Florida and proceeding north and west. Normal RSV seasons generally begin in the fall and peak in the winter. However, many states in the United States observed an unusual increase in RSV cases during the spring and summer of 2021 after near absence of RSV in the winter of 2020–2021.
An article published on May 12, 2023 on the preprint server medRxiv looked at real-time U.S. nationwide EHR data from January 1, 2010 through January 31, 2023 to assess whether COVID-19 contributed to the surge of RSV infections and hospitalizations in young children in fall 2022. After examining EHR data for over 29 million medical visits from children 0-5 and over 13 million medical visits for children 0-1, the authors concluded that prior COVID-19 infection increased risk for unspecified bronchiolitis (of which RSV is the most common cause) in both 2021 and 2022.
"Patients infected with COVID-19 can have long-lasting changes in both innate and lymphocyte based immune functions, precisely the systems most engaged in defense against respiratory viruses. These findings further support our hypothesis that COVID-19 had adverse impact on the immune and respiratory systems of children, making them susceptible to severe respiratory viral infections from RSV and other viruses."
While many hoped the pandemic was over, the fall of 2022 proved wrong. The 2022-2023 "cold and flu season" in the U.S. rivaled some of the worst seasons on record — two months earlier than expected. Weekly pediatric hospitalizations for RSV were the highest ever recorded in October 2022, and influenza, which normally peaks in February, has drove up December hospitalization rates to the highest in more than a decade. And while Covid illnesses were significantly lower than the previous two winter seasons, they too rose significantly in December 2022 through January 2023.
It's now spring 2023, and as RSV and flu season concludes, and Covid infections and hospitalizations are at an all time low. But something isn't right. Everywhere you go it seems like everyone is sick. Most people seem to be diagnosed with general "respiratory viral infections" (an umbrella term that either means not enough diagnostic tests were run, or the tests are not picking up infections [current strains of SARS-CoV-2 appear to be causing false negatives on both rapid antigen tests and PCR tests]).
Most of these general viral infections are your common respiratory viruses such as the common cold causing HCoVs (different from SARS-CoV-2 which causes COVID-19) and adenoviruses that are surging especially in young children. There's also been record number of Group A Streptococcal infections, including Strep Throat and Scarlet Fever.
There's also been outbreaks across the world of norovirus, rotavirus, and enteroviruses (which cause gastrointestinal issues like vomiting and diarrhea).
And on top of that there is an alarming increase in human metapneumovirus (HMPV) infections. While most people have likely had HMPV without ever knowing what it was, since it typically results in typical cold-like symptoms; in somecases -- which are most common among young children and elderly or immunocompromised adults -- HMPV can also lead to complications including bronchitis and pneumonia.
Other viruses that are capable of latent phases are:
Current research is also trying to determine whether SARS-CoV-2 (COVID-19) is capable of latent phases. If this turns out to be the case, it is possible that once a person has been infected with SARS-CoV-2, the virus may live in their body indefinitely, possibly reactivating at a later time, including with unique symptoms (i.e. the Varicella Zoster Virus which causes chicken pox can be reactivated years or decades after initial infection and cause Shingles (Herpes Zoster)).