You might want to ask your doctor about having a blood test for vitamin D levels. There is scientific evidence to show low levels can mean more respiratory infections. If low, then supplement. It's not expensive, and can be bought at Boots, H&B, and amazon. If very low, then doc may be able to prescribe.
It is used in the immune system, not just for bone metabolism.
There are also vaccines against some forms of pneumonia. Ask about these.
Just so you know, in 2002 I was diagnosed with asthma. After that, the good news about vitamin D became more widely known so I joined the lobby group campaigning for more widespread knowledge of its value. The bad news is that 85% of the population is deficient. (Rain, little sun, etc)
I was having constant colds, and they started to end up with pneumonia. 6 weeks off work sometimes, which meant my work was going to pot. So I started supplementing, starting with 2000 iu a day.
When I read that much higher doses did not lead to anything dire, I increased the dose gradually over time. My secondary chest infections disappeared, and eventually all my horrid colds and coughs. Still have asthma, but it is controlled with very low dose of medication. On the very rare occasions I do get a cold, it doesn't last. Just a day or so of a runny nose.
I must emphasise this is just one person's response. But you might search on the net to find the work being done.
Make sure you don't have any parathyroid problems, ask your doc. And make sure you both get real sunshine - no creams, but NEVER burn - and have a good diet with plenty of vitamins and trace elements. All used in the immune system.
Sunshine is good for you. It reduces blood pressure, and makes 'happy' chemicals. Lots of good chemicals made in the skin from cholesterol when exposed to sunshine, not just vit D. But NEVER burn.
Patients need to advocate for themselves now. So good luck.