Investigating the association between COVID-19 vaccination and outbreaks in care homes in Northern Ireland

Plain English Summary 

Care home residents and staff where among the first people in the UK to be offered COVID-19 vaccines after they became available in December 2020. 

In Northern Ireland (NI), this first vaccine roll-out mainly used the Pfizer BioNTech mRNA vaccine, BNT162b2. 

Unlike other UK nations, many residents and staff of Northern Irish care homes were given their second-dose vaccine 21-days after their first. This was before the policy change requiring a 12-week interval between doses was announced on 31 December 2020. 

Why did we carry out this work? 

People living in care homes are affected much more by COVID-19 than people who do not. This is because their age combined with any existing health conditions makes them vulnerable to severe outcomes of infection, meaning hospitalisation and death. 

A care home’s closed environment also means that, in the event of an outbreak, the SARS-CoV-2 virus is likely to spread quickly among residents and staff. 

Therefore, it is important that we monitor to see if the actions taken by public health authorities have been effective in protecting these priority groups, by preventing these outbreaks from occurring. 

We wanted to investigate: 

1. How many COVID-19 outbreaks happened in NI care homes (frequency)? 

2. How long did these outbreaks last (duration)? 

3. How do these results compare to if the vaccination programme had not happened? 

For the last point, we used modelling to predict these values. 

What did we do? 

Study Population 

On 18 November 2020, there were 480 care homes in NI. This includes both residential and nursing homes. 

Our data 

To determine how many COVID-19 outbreaks happened in NI care homes, we looked at data on Reverse Transcription Polymerase Chain Reaction (RT-PCR) tests. We also used this information to predict how many outbreaks would have occurred without the vaccination programme. 

Find out more about: What is PCR? 

We gathered these data from several routine sources, which were: 

• The Office of National Statistics  

  • We used data the ‘Estimated number of people testing positive for COVID-19' data for NI, as a measure of what proportion of the population was living with COVID-19. We looked at data ranging from 17 October 2020 to 6 November 2021. 

• The Public Health Agency (PHA) 

  • The PHA has summarised reports of data collected daily by care homes. 

• Care home outbreak surveillance  

  • The PHA’s Health Protection team was notified of any confirmed COVID-19 cases or outbreaks in care homes. This information was then extracted, cleaned and entered into a database. 

Definitions 

The table below shows the key definitions we used in this study. 

Term	Definition
Possible cases of COVID-19	Any resident or staff with COVID-19 or influenza-like symptoms
Confirmed cases of COVID-19	Positive Reverse transcription Polymerase Chain Reaction (RT-PCR) test from either residents or staff
COVID-19 outbreak	2+ possible or confirmed cases within a 14-day period
Confirmed COVID-19 outbreak	2+ confirmed COVID-19 cases among care home residents or staff within a 14-day period
Closed outbreaks	No new cases for 14 days after the most recent case

What did we find? 

How many care home outbreaks were there? 

We found that the introduction vaccination programme was associated with a two-thirds reduction in outbreak frequency, compared to if it had not been rolled-out. 

We estimate that without the vaccination programme, 1625 COVID-19 outbreaks would have occurred in NI care homes. However, we found that only 501 happened in real life. 

This effect was seen in both residential and nursing homes. 

How long did these outbreaks last? 

Our results showed that the duration of COVID-19 outbreaks was shorter in homes where the vaccine had been delivered. 

The hazard ratio of an outbreak ending (assuming a 21-day lag for immunity) was 2.53. This means that a care home with vaccinated staff and residents was 2.53 times more likely to end than if they were unvaccinated. 

Why do outbreaks still happen? 

There are several reasons why outbreaks may have occurred post-vaccination, such as: 

• Not everyone in a care home may have been fully vaccinated; 

• Not everyone who was fully vaccinated would have had full protection against infection; 

• Both the resident and staff populations are dynamic, with new people coming in who may not have been vaccinated beforehand. 

Why is this important? 

Our findings show that NI’s vaccination programme had a positive impact on COVID-19 outbreaks in care homes, minimising the number that occurred and how long they lasted. 

We can, therefore, say that the intervention brought about by the vaccination programme has been effective and successful in protecting these vulnerable groups of people. 

Note

This plain English summary was reviewed with the support and feedback of the DaC-VaP Patient and Public Involvement Leads.

Find out more on: Meet our team