#16,055
Three weeks ago, in CDC HAN: Increased RSV Reports Across The Southern United States, we looked at an unusual off-season surge in Respiratory Syncytial Virus across parts of the US after more than a year without appreciable non-COVID respiratory illness (see chart below).
As we've discussed often over the past year (see here, here, here, and here), this lack of exposure to common respiratory viruses - whether due to social distancing, NPIs (face masks, hand hygiene,etc.) or `viral interference' from COVID - is a double-edged sword.
- In the short run, it makes it easier to identify COVID cases, lessens the burden on healthcare delivery systems, and avoids the enhanced risks due to duel infections.
- But at the same time, this lack of exposure allows our community immunity to these viruses to wane over time, potentially setting us up for serious epidemics when they finally do return.
In 2017's PLoS Comp. Bio.: Spring & Early Summer Most Likely Time For A Pandemic, researchers cited `viral interference' and/or the temporary immunity hypothesis as possible reasons why historically pandemics almost always emerge in the spring or early summer; after the end of regular flu season.
Essentially the time of the year when our collective `shields' are down, or at their lowest.
It wouldn't take the rise of a novel virus to have a significant impact, however. The 2017-2018 H3N2 flu season was one of the deadliest in recent memory. A repeat of that - with or without COVID - would present a significant healthcare challenge.
In New Zealand, where it is now winter, seasonal respiratory viruses have begun to rise for the first time in more than a year. Leading the charge is RSV, which commonly affects small children, but can also infect older adults, sometimes with deadly results.
As a result, headlines from NZ media outlets the past few days have featured stories such as; Hospitals overrun with sick kids as winter viruses enter New Zealand. While a dramatic turn about from the past year or two, RSV levels in New Zealand are still lower than during many pre-COVID seasons.
We've a press release from New Zealand's Institute of Environmental Science and Research (ESR) - dated July 7th - which attempts to quantify the impact their current RSV outbreak, which they describe as a `very sharp' rise and an `exponential increase'.
ESR data highlights surge of respiratory syncytial virus (RSV)
Weekly data collected by the Institute of Environmental Science and Research (ESR) is providing health experts with critical information about the outbreak of RSV currently being experienced across New Zealand.
ESR virologist Dr Sue Huang says weekly numbers reported by the national virus laboratory network started climbing sharply in June, reaching 538 cases for the week 25 ending 27 June 2021.
“Early warning can lead to increased vigilance to allow health authorities to target public health advice and measures. At the moment the rates of RSV are still shooting upwards and have yet to reach a plateau,” says Dr Huang.
“While there were sporadic cases previously, the increase of RSV cases in New Zealand in 2021 was reported by the national viral laboratory network shortly after re-opening the borders with Australia in late-April.”
ESR’s laboratory-based virology report for 1 January to 27 June 2021 taken from the six hospital laboratories based from Auckland to Dunedin, plus the national ESR virology laboratory, reported only 20 sporadic RSV cases until late May when weekly numbers started growing. By mid-June the numbers reached over 100 a week, and then 538 two weeks later.
To date, 969 RSV cases have been reported in just five weeks by ESR’s laboratory network, compared with an annual average of 1,743 cases during the winter period (weeks 18-39) reported in the five years (2015-2019) before COVID-19.
“The exponential increase is very sharp. The absence of RSV last winter meant there is a young cohort of children from last year, plus a new cohort this year, who have not been exposed to the seasonal virus,” says Dr Huang.
“So overall, our population has more people who are more susceptible to RSV infection. There is no vaccine against RSV. The best way to prevent spread of the infection is to always practice good respiratory hygiene, especially people with symptoms that might be due to RSV (or other respiratory viruses).”
Despite the sharp increase, rates of RSV infection are still less than pre-COVID levels. Dr Huang says ongoing research in tackling RSV is critical.
“Studies like the WellKiwis infant study are following children and households to see how the first exposure to the flu or flu vaccine influences their ongoing immune response to the flu as children grow, and how the flu is spread between household members. This will hopefully lead to a universal flu vaccine for everyone, prevent pandemics and save lives.”
We'll obviously be watching the winter respiratory season in the Southern Hemisphere closely for clues as to what we might expect this fall and winter in the Northern Hemisphere.
On this same general topic, yesterday the European Society of Clinical Microbiology and Infectious Diseases - in advance of this year's online ECCMID 2021 conference - published the following press release on the current absence - and inevitable return - of seasonal respiratory viruses.
NEWS RELEASE 7-JUL-2021
Striking absence of flu and other "usual suspects" during COVID-19 pandemic
EUROPEAN SOCIETY OF CLINICAL MICROBIOLOGY AND INFECTIOUS DISEASES
Cases of flu and respiratory syncytial virus (RSV) fell significantly in both adults and children during the COVID-19 pandemic, according to new research being presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) held online this year.
Influenza A and influenza B (which both cause flu) and RSV are common causes of respiratory infections, particularly in winter. There are 9 to 45 million of cases of flu in the US each year. RSV is particularly common in under-twos but can affect people of all ages.
The retrospective study, by Ms Siri Sarvepalli and colleagues at Wayne State University, Detroit, USA, looked at whether the incidence of these and other respiratory infections fell during the COVID-19 pandemic.
It involved comparing the results of PCR tests for various infections carried out at the Detroit Medical Centre (DMC) and Children's Hospital of Michigan (CHM) between September 2019 and February 2020 with the results from September 2020 to February 2021.
The PCR tests used samples from nasopharyngeal swabs to test for influenza A and B, RSV and SARS-COV-2. Samples from throat swabs were used in PCR tests for Group A Streptococcus (GAS), a bacterial throat infection that typically follows viral upper respiratory tract infections.
Data on other respiratory virus infections was also reviewed.
For adults, in the 2019-2020 season, 11.5% of influenza A, 13.1% of influenza B, and 9% of RSV tests were positive. In the 2020-2021 season, 0% of influenza A, influenza B, and RSV tests were positive.
For children, in the 2019-2020 season, 12.4% of influenza A, 20.2% of influenza B, and 23.7% of RSV tests were positive. In the 2020-2021 season, 0% of influenza A and influenza B returned positive. One RSV test was positive.
The number of tests for GAS was dramatically reduced compared to the previous year. Some 933 GAS tests were carried out in adults in the 2019-20 period (of which 22.8% were positive), compared to 212 (23.11% were positive) a year later. For children, the figure fell from 3,984 tests (of which 27% were positive) to 777 (20.98% positive). See table in link below.
Incidence of other, less common, respiratory viruses had also fallen. In 2019-2020, the proportion of tests for other respiratory viruses that came back positive ranged from 0.2-4.2% (Parainfluenza virus 1: 3.5%, parainfluenza virus 2: 0.4%, human metapneumovirus: 4.2%, Coronavirus 229E: 0.2%) as compared to 0% in 2020-2021 - a change described as "remarkable" by the study's authors. Data on these infections from 42 medical centres across the Midwest of the US revealed a similar pattern across the entire region. (see table 3 of poster - and link to table of results see this link: https://drive.google.com/file/d/1MZIWUxOqtLIu_SRAyOcoFITqGJiY2pcb/view)
The researchers say: "The incidence of influenza A and B and RSV infections in the 2020-2021 season decreased significantly compared to the 2019-2020 season in both paediatric and adult populations. Community mitigating measures such as social distancing, school closures and use of masks may have decreased the spread of viral pathogens. This may also explain the decrease in GAS infections, which typically occur after an infection with a respiratory virus."
In addition, infection with COVID-19 may have protected people against other respiratory viruses, through viral interference. This occurs when one virus temporarily blocks a co-infection from another virus and was seen during the H1N1 "swine flu" pandemic in 2009.
Similar reductions in incidence of influenza and other respiratory viral infections have been noted elsewhere, including in the southern hemisphere where Australia, Chile and South Africa reported just 51 cases of flu in total in the 2020 flu season.
Ms Sarvepalli says: "It is likely that the number of cases of flu and other respiratory infections will rise back to normal in the coming years as SARS-CoV-2 becomes a seasonal virus.
"However, if handwashing and other mitigating measures are followed to the same extent as last winter, numbers could instead remain lower than usual."
Whether `flu' returns to normal this year or next - or lobs something even more problematic in our direction - is unknowable. We are in uncharted territory, and what happens over the next year or two will depend as much upon COVID - and our ongoing response to the pandemic - as it does on any emerging or re-emerging respiratory viruses.
A trait we would do well to emulate going forward.But viruses have been around much longer than we have, and they owe much of their longevity to their ability to adapt in the face of new threats.
