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 There is some research on birth season and infant illness risk in the first year, including patterns that suggest babies born in certain seasons (like spring or summer) can experience more symptomatic infections during their first winter/RSV season — although the evidence specifically for preterm infants is more about baseline risk of severe disease and seasonal RSV dynamics rather than a definitive paper stating “summer-born preterm infants have higher overall unwellness in first winter.”

Key studies and papers you can cite

Respiratory illness and birth season

• Infants born in spring/summer have higher risk of RSV in their first respiratory season. A study reported that infants born during spring and summer months had a higher rate of medically attended respiratory syncytial virus (RSV) infection during their first season of risk compared to other birth periods. 
  Journal of the Pediatric Infectious Diseases Society (reported via Healio) found this seasonal pattern for RSV incidence.

Seasonal timing and RSV epidemiology

• Infants born just before the RSV season or during low-exposure months (e.g., late spring/summer) often encounter their first winter when they are still very young and immunologically naive, which seems to correlate with higher RSV and bronchiolitis hospitalisation rates. 
  RSV seasonality papers show that timing of birth relative to peak community virus circulation matters for risk.

Preterm infants and infection risk

• Although not season-specific, numerous studies document that preterm infants are at higher risk of severe respiratory illness, including RSV, especially in their first winter, due to lung immaturity and weaker immune responses. 
  This underlies the clinical rationale for prophylaxis (e.g., palivizumab) in premature infants starting before winter.  

What the literature does not yet clearly show

• There aren’t (to my knowledge) large cohort studies specifically focused on summer-born preterm infants being more unwell overall in their first winter compared with other preterm birth seasons. Most research focuses either on:
  
• Season of birth and RSV risk in general infant populations
• Seasonal patterns of preterm birth incidence
• Baseline high risk in preterm infants irrespective of birth month
• 
  

However, the indirect evidence above (higher RSV incidence for summer/spring births combined with high vulnerability of preterm infants) is consistent with the hypothesis you’re interested in.

Papers / references you might request access to

Here are specific articles worth citing directly if you can access them (via institutional subscription or research networks):

1. Journal of the Pediatric Infectious Diseases Society: Seasonal birth month and risk of medically attended RSV in infants. (2024) – Reports higher first-season RSV in spring/summer births.  
2. Infectious Disease Advisor / epidemiological analyses: Infants born May–September have the highest risk for medically attended RSV-associated lower respiratory tract infection.  
3. Respiratory Syncytial Virus Seasonal Patterns literature: Timing of birth relative to RSV season affects likelihood of early infection.  
4. Preterm infant RSV risk literature: Reviews and trials documenting higher risk of severe RSV disease in preterm infants.  

Clinical context

• Because preterm infants are inherently more vulnerable to respiratory infection and decompensation (lung immaturity, smaller airways, altered immunity), clinicians already consider them high-risk during winter viral seasons.  
• Seasonal timing (summer birth → first cold season shortly after leaving maternity wards) is often factored into RSV prophylaxis decisions in high-risk infants (e.g., palivizumab or nirsevimab).  

If you need the full references or PDFs for any of the studies above (e.g., for a paper or grant application), I can help you track down direct publication links or DOIs where available.