“You do realise it’s July, don’t you? I mean I know we’ve all been locked in our houses for months, it’s raining and the radio played a Christmas song this morning…but it’s still summer!” exclaimed the Microbiologist.
So, in any other year this would be a weird request. Some infections are truly seasonal; influenza comes in the winter, Campylobacter comes after BBQ season and at Christmas when people don’t cook poultry properly AND Respiratory Syncytial Virus is also most definitely a winter problem. Or is it?
Respiratory Syncytial Virus (RSV)
RSV, as the name suggests, is a virus that infects the respiratory tract. It is very common. In older children and adults it usually causes a mild respiratory infection; a bit of a cold and a cough. Very occasionally these “older people” get a flu-like illness and take to their beds for a few days, take Lemsips and eat chicken soup but they usually recover fully without any medical intervention.
However, RSV can have devastating consequences for immunocompromised patients, especially those who have had a bone marrow transplant. I am aware of a historical outbreak of RSV on an adult bone marrow transplant unit where the mortality was 70%! That’s even higher than the Ebola outbreak in West Africa in 2013!
The classic severe RSV illness occurs in infants and is called bronchiolitis. Infants get severe inflammation of the lungs which stops them being able to get enough oxygen into their blood. They cannot feed properly as they cannot breathe and so become rapidly dehydrated. It is a potentially life-threatening infection.
It is pretty easy to “spot” the child with bronchiolitis as they have a distinctive “wet cough” which every Paediatrician can recognise.
There is no specific treatment for RSV. The antiviral Ribavirin can be used but it makes little difference (although it can potentially be enough to save the life of a very sick person). Most of the treatment of RSV is supportive with oxygen, ventilation and fluids.
Some infants are particularly at risk of severe bronchiolitis during their first winter (e.g. chronic lung disease due to prematurity, congenital heart disease, congenital immunocompromise) and so are given passive immunity with an anti-RSV immunoglobulin called Palivizumab once a month throughout RSV season to prevent them getting infected. But this is July!
So what is RSV season? When are infants at risk, and when do we routinely test for RSV and use drugs like Palivizumab?
The graph below shows the "normal RSV season", slowing building up from October (weeks 40-43) to peak around Christmas, before settling in February (weeks 5-9).
Okay, now take a look at this graph of RSV rates for 2020 to 2021, boring it isn’t… what’s that peak in summer!?!
But look again… RSV rates are now climbing up to normal winter levels and yet the figures for “week 29”, to the right of the graph, are for July! What is going on? RSV in the summer, you cannot be serious! [Stop it!!! Wimbledon finished 4 weeks ago, 28 Jun 2021 – 11 Jul 2021]
Look at the week numbers. Rates started rising in week 21, and then really kicked off again in week 29. So, what are those weeks as dates? Week 21 is the 24th May and week 29 is the 19th July… sound familiar? On the 24th May we were all allowed to start socially interacting again and travel restrictions were reduced, and everyone probably knows the 19th July was “Freedom Day”! Coincidence? I think not….
So why might RSV season be early?
I think this is the wrong question… [Okay, I asked it!] I think RSV season is actually late!
There will be a number of reasons why RSV infections occur in winter:
- Waning immunity since the last season
- Increased population of infants born since the last season and not immune
- Antigenic drift in the virus meaning past infection is less protective against any new variant
- Close indoor social contact allowing more efficient viral spread
What our Covid-19 restrictions have done (other than reduce the numbers of Covid-19 cases) is to:
- Increase the period of time between RSV seasons allowing further waning of immunity
- Increase the period of time during which babies have been born without being exposed to RSV, increasing the size of the vulnerable population
- Increase the time for antigenic drift to occur, meaning the virus may be more different than previous viruses and hence less well recognised by past immunity
- Reduced social contact restrictions meant more people “rushed off” to see relatives and spread their viruses around
When the Covid-19 restrictions were then relaxed on the 24th May, and then again on the 19th July, we had the perfect situation for ANY respiratory virus that would normally have spread in the winter to start spreading in the summer instead. All told, the relaxing of Covid-19 restrictions was a benefit to ALL respiratory viruses, and RSV has taken full advantage!
Where the RSV has “suddenly” come from isn’t completely clear. There are two possibilities:
- As borders have reopened, we have allowed RSV back into the country and it has then rapidly spread
- RSV has always been here causing more chronic infections in a few individuals or even circulating within very small, isolated groups and when restrictions were lifted, and these individuals or groups mixed with everyone else the virus has rapidly spread
I favour the first explanation as it fits best with how I think of viruses like RSV. Personally, I don’t think of any virus being especially “seasonal” but rather “migratory”. Once a virus has infected as many people as it can within an area it will spread, if possible, to somewhere where there are new, non-immune, people to infect. It’s a bit like birds migrating south from the UK for the winter; as their normal food source disappears in winter, they head south to find new food, when that food disappears at the “destination”, usually entering the destination’s winter, the birds head north again where the original food source has recovered… at the end of the day the human population may be just “migratory virus food”. Currently we have a population which avoided exposure to RSV last winter due to Covid-19 precautions so when RSV has returned it’s found a vast non-immune population, RSV is “feasting” on non-immune people!
Is this only happening in the UK?
Nope, this has already happened in the Southern hemisphere. There is a great study from Australia which showed RSV last “Australian summer” (our winter) did exactly the same thing there.
Australia implemented strict Covid-19 precautions which appear to have prevented any RSV infections as well, however when these precautions were relaxed RSV infections started to occur, starting in spring, and going into summer. Case numbers were higher, and infections were more severe, with more hospital admissions.
The authors quite rightly suggest that the same could happen to other respiratory viruses, not just RSV. This may mean that flu season could come early in the UK and be more severe. This is especially the case as we don’t start vaccinating against influenza until about October time in the UK, and that may be too late this year. Now that’s a scary thought for you!
So yes, it appears that we should probably throw out the “rule book” for when to start testing patients for respiratory viruses for the time being. We shouldn’t assume that because it is summer we won’t see RSV or influenza… in fact we “should actually expect it” and plan for it. Maybe we should already be looking for RSV and Influenza Viruses in our patients with respiratory infections? Maybe we should start giving Palivizumab early this year to vulnerable infants? And maybe it would be a good idea to try and start our flu vaccination programs as soon as possible? If we don’t, we may regret it later…
And on that cheerful note I’m off to check the weather forecast… find my “Now that’s what I call Christmas” CD and put the heating on! Or maybe a long overdue “summer” heat wave will allow us all back outdoors and help us to stop spreading viruses around!